Patent Publication Number: US-2023138791-A1

Title: Fan module, and portable air purifier having same

Description:
TECHNICAL FIELD 
     Disclosed herein is a fan module for suctioning and discharging air and a portable air purifier having the same. 
     BACKGROUND ART 
     Air purifiers are widely used in our daily lives. The devices can filter physical particles such as dust, fine dust, ultra fine dust and the like, chemical substances such as odorant particles, harmful gases and the like, and microorganisms such as germs, viruses and the like, in air, to purify the air. 
     People cannot live without air purifiers in an industrial society since more and more people are greatly affected by fine dust and suffer from allergies. Accordingly, there is a growing demand for the device. 
     Ordinarily, a large-sized air purifier is used in a house that is 100 square meters or greater. The air purifier can be provided with a filter for physical particles such as dust and the like, a filter for chemical substances such as gas and the like, and a filter for microorganisms such as germs, viruses and the like, in combination. That is, such a large-sized air purifier capable of accommodating various types of filters can be used in a large space. 
     However, air purifiers are rarely used in a narrow space such as a studio apartment, a space in a vehicle and the like, or in a very wide space such as a public library and the like or an outdoor space, considering space availability, portability and energy efficiency. Additionally, a user who moves from place to place usually uses an air purifier small enough to carry. Under the circumstances, there is a growing need for a portable air purifier that is easy to carry for use. 
     Portable air purifiers need to be small and lightweight enough for users to carry such that the users can easily carry and use the portable air purifiers anywhere. That is, the devices are useful for people who often go out and move from place to place instead of staying in a place such as a house. 
     The amount of purified air discharged from a portable air purifier is less than the amount of purified air discharged from an ordinary air purifier that is installed in a place. Additionally, the portable air purifier discharges purified forward in a narrower range than the ordinary air purifier. The portable air purifier has the above problems inherently, since the portable air purifier has a small size. As the size of the portable air purifier decreases, it is difficult to increase the amount of discharge of purified air and the range of forward discharge of purified air. 
     A decrease in the amount of discharge of purified air and the range of forward discharge of purified air of the portable air purifier makes it difficult for air purified by the portable air purifier to reach a user, in particular, a user’s face. The portable air purifier’s failure in reaching the user’s face means that the portable air purifier cannot provide air purification performance properly. 
     DISCLOSURE 
     Technical Problem 
     One objective of the present disclosure is to provide a fan module that is compact and lightweight and has an improved structure enabling purified air to reach a user’s face effectively and a portable air purifier including the fan module. 
     Another objective of the present disclosure is to provide a fan module that is easily molded using a mold and has excellent discharge performance and a portable air purifier including the fan module. 
     Still another objective of the present disclosure is to provide a fan module that ensures excellent discharge performance at fixed pressure and a portable air purifier including the fan module. 
     Yet another objective of the present disclosure is to provide a fan module that suppresses an increase in noise and also has excellent discharge performance and a portable air purifier including the fan module. 
     Technical Solution 
     According to one aspect, in a fan module according to one aspect, a front end projection part is provided at a front end in a rotation direction of a fan blade included in a fan, and the front end projection part protrudes forward in the rotation direction from the front end of the fan blade in the rotation direction. 
     At least a part of the front end projection part may protrude further forward in the rotation direction than a connection point between the front end of the fan blade in the rotation direction and a shroud. 
     According to another aspect, a front end projection part is provided at a front end of a fan blade in a rotation direction provided in a fan, and the front end projection part protrudes forward in the rotation direction and toward one side in an axial direction from the front end of the fan blade in the rotation direction. 
     Accordingly, a shape of the fan blade may be designed in a way that an area of a region capable blowing of a larger amount of air than another region increases, and a stiffness of the fan blade is also improved. 
     Additionally, the front end projection part may not protrude further than the shroud toward one side in the axial direction, and a fan blade rear surface may be formed in a flat shape. 
     Accordingly, the shape of the fan blade may be changed without an increase of the number of molds used in molding of a conventional fan. 
     Additionally, according to another aspect, a fan blade front surface is formed in a shape which connects a leading edge and a trailing edge in a curved shape that is convex toward one side in an axial direction, and a fan blade rear surface is formed in a shape which connects the leading edge and the trailing edge straightly. 
     In a fan module having such a structure, as a camber is formed on only a front surface of a fan blade, molding using a mold is easily performed, and excellent discharge performance at fixed pressure may be provided. 
     According one aspect of the present disclosure, a fan module may include a shaft which extends in an axial direction; a motor which includes a stator and a rotor which rotates about the shaft; and a fan which includes a hub, a shroud, and a fan blade, wherein the hub may rotate along with the rotor and the shaft, the shroud may be disposed outside the hub in a radial direction, and the fan blade may protrude from the hub in a centrifugal direction and connect the hub and the shroud, wherein the fan may further include a front end projection part which protrudes forward in a rotation direction from a front end of the fan blade in the rotation direction, and at least a part of the front end projection part may protrude forward in the rotation direction further than a front end reference line which is a straight line which connects a connection point of the front end of the fan blade in the rotation direction and the hub and a connection point of the front end of the fan blade in the rotation direction and the shroud. 
     The fan blade may include a leading edge which is disposed at the front end in the rotation direction and formed to be straight; a trailing edge which is disposed at a rear end in the rotation direction and formed to be straight; a shroud chord which connects one end of the leading edge and one end of the trailing edge and extends in an inner circumferential surface of the shroud; and a hub chord which connects the other end of the leading edge and the other end of the trailing edge and extends in an outer circumferential surface of the hub, wherein the front end projection part may protrude from the leading edge and protrudes further forward than the shroud chord in the rotation direction. 
     The shroud chord may be obliquely formed with a predetermined slant angle in a way that the shroud chord is disposed at one side in the axial direction from the trailing edge side toward the leading edge side, and the front end projection part may form a slant angle parallel with the slant angle of the shroud chord and protrude from the leading edge, for example. 
     The front end projection part may be disposed in a way that a foremost side projection point of the front end projection part is closer to the shroud than the hub, for example. 
     The front end projection part may protrude further toward the one side in the axial direction as being closer to the foremost side projection point of the front end projection part from the other end side of the leading edge, for example. 
     The front end projection part may be formed in a way that the other end of the leading edge and the foremost side projection point of the front end projection part are roundly connected, for example. 
     The front end projection part may be formed into a curved shape convex toward the trailing edge side, for example. 
     The front end projection part may be formed in a shape in which a ratio of a distance between the foremost side projection point of the front end projection part and the hub and a distance between the foremost side projection point of the front end projection part and the shroud is in the range of 3:1 to 5:1, for example. 
     The fan blade may include a fan blade front surface and a fan blade rear surface each connecting the leading edge and the trailing edge, the fan blade front surface may be disposed further forward than the fan blade rear surface in the rotation direction, and the fan blade front surface and the fan blade rear surface may be formed into shapes different from each other, for example. 
     The fan blade front surface may be formed in a shape which connects the leading edge and the trailing edge into a curved surface that is convex toward one side in the axial direction, and the fan blade rear surface may be formed in a shape which connects the leading edge and the trailing edge straightly, for example. 
     The front end projection part may not protrude further than the shroud toward one side in the axial direction, for example. 
     The fan module may include a mixed flow fan which suctions air in the axial direction and discharges the air in a direction between the axial direction and the radial direction, for example. 
     According to another aspect of the present disclosure, a portable air purifier may include a case in which a suction surface is disposed at one side in an axial direction and a discharge surface is disposed at the other side in the axial direction; a filter disposed between the suction surface and the discharge surface; and a fan module disposed between the discharge surface and the filter, wherein the fan module may include: a shaft which extends in the axial direction; a motor which includes a stator and a rotor which rotates about the shaft; and a fan which includes a hub, a shroud, and a fan blade, wherein the hub may rotate along with the rotor and the shaft, the shroud may be disposed outside the hub in a radial direction, and the fan blade may protrude from the hub in a centrifugal direction and connect the hub and the shroud, the fan may further include a front end projection part which protrudes forward in a rotation direction from a front end of the fan blade in the rotation direction, and at least a part of the front end projection part may protrude forward in the rotation direction further than a front end reference line which is a straight line which connects a connection point of the front end of the fan blade in the rotation direction and the hub and a connection point of the front end of the fan blade in the rotation direction and the shroud. 
     Advantageous Effects 
     A portable air purifier according to the present disclosure is provided with a fan having the same weight and size as an axial flow fan and capable of discharging purified air to a wider area and farther away than the axial flow fan. The portable air purifier is compact and lightweight, allows purified air to reach a user’s face effectively, and ensures improvement in air purification performance. 
     In addition, the present disclosure provides a fan module that is easily molded using molds and has excellent discharge performance by changing a shape of a fan blade without an increase of the number of molds that are conventionally used for molding a fan so as to increase an air contact area of the fan blade and improve the rigidity of the fan blade and the performance of the fan blade at fixed pressure. 
     Further, the present disclosure provides excellent discharge performance at fixed pressure while easily molding using the molds by forming a camber on a front surface of the fan blade. 
     Furthermore, according to the present disclosure, the shape of the fan blade is designed in a way that an area of a region that blows a larger amount of air than other regions expands and the rigidity of the fan blade is improved. 
     Thus, according to the present disclosure, the portable air purifier capable of suppressing an increase in noise and having excellent discharge performance is provided. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front perspective view showing the front surface side of a portable air purifier of one embodiment. 
         FIG.  2    is an exploded perspective view showing a state in which the portable air purifier in  FIG.  1    is exploded. 
         FIG.  3    is rear perspective view showing the rear surface side of the portable air purifier in  FIG.  1   . 
         FIG.  4    is a cross-sectional view along line “IV-IV” in  FIG.  1   . 
         FIG.  5    is a front perspective view separately showing a case in  FIG.  1   . 
         FIG.  6    is a rear perspective view separately showing the case in  FIG.  1   . 
         FIG.  7    is a cross-sectional view specifically showing the structure of portion “VII” in  FIG.  4   . 
         FIG.  8    is a perspective view separately showing a fan module of one embodiment. 
         FIG.  9    is a perspective view separately showing a fan case in  FIG.  8     
         FIG.  10    is a front view separately showing the fan in  FIG.  8   . 
         FIG.  11    is a side view showing the fan in  FIG.  10   . 
         FIG.  12    is a cross-sectional view along line “X II - X II” in  FIG.  11   . 
         FIG.  13    is an exploded perspective view separately showing a fan cover and a fan module. 
         FIG.  14    is an exploded perspective view separately showing a fan module, a fan base and a filter. 
         FIG.  15    is a rear perspective view showing the rear surface of a fan base. 
         FIG.  16    is a perspective view showing a coupling state between the fan base and the filter. 
         FIG.  17    is a view showing an aspect of the air flow of the portable air purifier of one embodiment. 
         FIG.  18    is a front perspective view showing a front surface side of a fan provided in a portable air purifier of another embodiment. 
         FIG.  19    is a rear perspective view showing a rear surface side of the fan in  FIG.  18   . 
         FIG.  20    is a front view showing the front surface side of the fan in  FIG.  18   . 
         FIG.  21    is an enlarged view showing portion “XXI” in  FIG.  20   . 
         FIG.  22    is an enlarged view showing portion “XXII” in  FIG.  21   . 
         FIG.  23    is a cross-sectional view along line “XXIII-XXIII” in  FIG.  20   . 
         FIG.  24    is a front view showing a slide direction of a mold used for molding the fan of another embodiment. 
         FIG.  25    is a side cross-sectional view showing the slide direction of the mold in  FIG.  24   . 
         FIG.  26    is a graph showing a measurement result of a flow rate with respect to a fan speed of the portable air purifier of another embodiment. 
         FIG.  27    is a graph showing a measurement result of a noise with respect to the flow rate of the portable air purifier of another embodiment. 
     
    
    
     MODES OF THE INVENTION 
     The above-described aspects, features and advantages are specifically described hereunder with reference to the accompanying drawings such that one having ordinary skill in the art to which the present disclosure pertains can easily embody the technical spirit of the disclosure. In the disclosure, detailed description of known technologies in relation to the subject matter of the disclosure is omitted if it is deemed to make the gist of the disclosure unnecessarily vague. Below, preferred embodiments according to the disclosure are specifically described with reference to the accompanying drawings. In the drawings, identical reference numerals can denote identical or similar components. 
     The terms “first”, “second” and the like are used herein only to distinguish one component from another component. Thus, the components should not be limited by the terms. Certainly, a first component can be a second component unless stated to the contrary. 
     When one component is described as being “in the upper portion (or the lower portion)” or “on (or under)” another component, one component can be directly on (or under) another component, and an additional component can be interposed between the two components. 
     When any one component is described as being “connected”, “coupled”, or “connected” to another component, any one component can be directly connected or coupled to another component, but an additional component can be “interposed” between the two components or the two components can be “connected”, “coupled”, or “connected” by an additional component. 
     Throughout the disclosure, each component can be provided as a single one or a plurality of ones, unless stated to the contrary. 
     In the disclosure, singular forms include plural forms as well, unless explicitly indicated otherwise. It is to be understood that the terms such as “comprise” or “include” and the like, when used in this disclosure, are not interpreted as necessarily including stated components or steps, but can be interpreted as excluding some of the stated components or steps or as further including additional components or steps. 
     Throughout the disclosure, the terms “A and/or B” as used herein can denote A, B or A and B, and the terms “C to D” can denote C or greater and D or less, unless stated to the contrary. 
     First Embodiment of Portable Air Purifier 
     Exterior of Portable Air Purifier 
       FIG.  1    is a front perspective view showing the front surface side of a portable air purifier of one embodiment, and  FIG.  2    is an exploded perspective view showing a state in which the portable air purifier in  FIG.  1    is exploded.  FIG.  3    is rear perspective view showing the rear surface side of the portable air purifier in  FIG.  1   , and  FIG.  4    is a cross-sectional view along line “IV-IV” in  FIG.  1   . 
     In the embodiment, a portable air purifier  50  is described as an example. 
     Referring to  FIGS.  1  to  4   , the portable air purifier  50  in the embodiment may be approximately formed into a cuboid. The portable air purifier  50  includes a case  520 , a front surface panel  510  and a rear surface panel  570 . 
     The case  520  forms the skeleton of the exterior of the portable air purifier  50 . Various types of components are accommodated in the case  520 . 
     Both sides of the case  520  in a first direction may be open. That is, the front and the rear of the case  520  may be open. A suction surface may be disposed on one side of the case  520  in the first direction, and a discharge surface may be disposed on the other side of the case  520  in the first direction. 
     For example, the suction surface may be disposed at the rear of the case  520 , and the rear surface panel  570  may be disposed at the rear of the case  520 , where the suction surface is disposed. Additionally, the discharge surface may be disposed at the front of the case  520 , and the front surface panel  510  may be disposed at the front of the case  520 , where the discharge surface is disposed. 
     The suction surface may indicate a virtual surface corresponding to the boundary between the inside of the case  520  and the outside of the case  520 , at the rear of the case  520 . The discharge surface indicates a virtual surface corresponding to the boundary between the inside of the case  520  and the outside of the case  520 , at the front of the case  520 . 
     In the embodiment, the suction surface and the discharge surface may actually be openings formed at the rear and the front of the case  520 , since both the rear and the front of the case  520  are open. In the embodiment, the suction surface and the discharge surface are disposed in parallel, for example. 
     The front surface panel  510  is coupled to the front of the case  520 . The front surface panel  510  forms the exterior of the front surface of the portable air purifier  50 . 
     The rear surface panel  570  is coupled to the rear of the case  520 . The rear surface panel  570  forms the exterior of the rear surface of the portable air purifier  50 . 
     The portable air purifier  50  may be entirely formed into a standing cuboid that is elongated in the up-down direction. Accordingly, a user may use the portable air purifier  50  in the state in which the portable air purifier  50  stands or lies. Additionally, the portable air purifier  50  may stay in the same position reliably without rolling in a moving vehicle, even if the portable air purifier  50  is used in the state in which the portable air purifier  50  lies. 
     Directions are defined as follows. A direction from the case  520  to the front surface panel  510  is referred to as a front, and a direction from the case  520  to the rear surface panel  570  is referred to as a rear. At this time, a “first direction” denotes the front-rear direction. Additionally, the first direction may have the same meaning as the axial direction. The axial direction may be defined as a parallel direction with the lengthwise direction of a shaft disposed at a fan module  540  that is described below. A “second direction” is a direction perpendicular to the first direction and denotes the left-right direction. A “third direction” is a direction perpendicular to the first direction and the second direction and denotes the up-down direction. 
     Entire Structure of Portable Air Purifier 
     The portable air purifier  50  in the embodiment includes a front surface panel  510 , a case  520 , a fan cover  530 , a fan module  540 ,  545 , a filter module  550 , a battery  560 , a rear surface panel  570  and a rear surface cover  580 . 
     The front surface panel  510  is disposed at the foremost side of the portable air purifier  50  and forms the exterior of the front surface of the portable air purifier  50 . Air purified by the portable air purifier  50  is discharged outward through the front surface panel  510 . To this end, a plurality of outlets  510   a  is provided on the front surface panel  510 . 
     The case  520  forms the skeleton of the exterior of the portable air purifier  50 . The exteriors of the upper surface, lateral surfaces and lower surface of the portable air purifier  50  are formed by the case  520 . Accommodation space is formed in the case  520 . Various types of components such as a fan cover  530 , a fan module  540 ,  545 , a battery  550 , a filter module  560  and the like, constituting the portable air purifier  50 , are accommodated in the accommodation space. The case  520  has enough strength to protect the accommodated components from an external impact, for example. 
     The fan cover  530  is accommodated in the accommodation space of the case  520  and disposed at the front of the fan module  540 ,  545 . That is, the fan cover  530  is disposed between the front surface panel  510  and the fan module  540 ,  545 , inside the case  520 . 
     The fan cover  530  fixes the fan module  540 ,  545  to the inside of the case  520 . Additionally, the fan cover  530  also induces air being blown by the fan module  540 ,  545  to flow straight toward the front, without causing the spread of the air to surrounding areas. Further, the fan cover  530  may be involved in fixing the filter module  550  and the battery  560 . 
     The fan module  540 ,  545  may be accommodated in the accommodation space of the case  520 , and disposed between the discharge surface and the filter module  550 . Specifically, the fan module  540 ,  545  may be disposed between the fan cover  530  and the filter module  550 . That is, the fan module  540 ,  545  is disposed at the rear of the fan cover  530  and the front of the filter module  550 . The fan module  540 ,  545  suctions air from the rear of the portable air purifier  50  and discharges air to the front of the portable air purifier  50 . 
     In the embodiment, the fan module  540 ,  545  includes a mixed flow fan respectively, for example. The fan module  540 ,  545  may suction air having passed through the filter module  550  in the axial direction and discharge the air in a direction between the axial direction and the radial direction. 
     The filter module  550  is accommodated in the accommodating space of the case  520  and disposed between the fan module  540 ,  545  and the rear surface panel  570 . That is, the filter module  550  is disposed at the rear of the fan module  540 ,  545  and the front of the rear surface panel  570 . 
     The filter module  550  purifies air suctioned through the rear of the portable air purifier  50 . The air that is purified while passing through the filter module  550  passes through the fan module  540 ,  545 , the fan cover  530  and the front surface panel  510  and then is discharged from the front of the portable air purifier  50 . 
     The filter module  550  may include a filter case  551  and a filter  559 . 
     The filter case  551  forms the skeleton of the exterior of the filter module  550 . In the embodiment, the filter case  551  is formed into a cuboid, the rear surface of which is open, for example. Insertion space for accommodating the filter  559  is formed in the filter case  551 . The rear of the filter case  551  is open. Accordingly, a passage for inserting the filter  559  into insertion space in a case main body part  552  is formed. 
     The filter  559  is mounted in the insertion space of the filter case  551 . The filter case  551  may be provided with a mounting groove or a mounting projection that allows the filter  559  to be firmly mounted in the filter case  551 , on the inner surface thereof. 
     Additionally, the filter case  551  is provided with a penetration hole  552  that forms a passage between the insertion space and the fan module  540 ,  545 . The penetration hole  552  is formed in a way that penetrates in the front-rear direction on the front surface of the filter case  551 . The penetration hole  552  forms a passage for allowing air having passed through the filter  559  to flow toward the fan module  540 ,  545 . 
     A plurality of penetration holes  552  is formed on the front surface of the filter case  551 , and each of the penetration holes  552  is formed in a way that penetrates in the front-rear direction on the front surface of the filter case  551 . 
     In the embodiment, a plurality of penetration holes  552  is provided on the front surface of the filter case  551 , and each penetration hole  552  is formed into a hexagon, for example. The plurality of penetration holes  552  is arranged in the form of a honeycomb. Accordingly, a honeycomb structure may be formed on the front surface of the filter case  551 . 
     The honeycomb structure, formed on the front surface of the filter case  551  as described above, ensures improvement in the rigidity of the filter case  551 , makes the filter case  551  lightweight as well as ensuring a passage for allowing air to flow. 
     The battery  560  is accommodated in the accommodation space of the case  520 , and disposed under the fan module  540 ,  545  and the filter module  550 . The battery  560  can supply a power source for driving the portable air purifier  50 . To this end, the battery  560  may be electrically connected to the fan module  540 ,  545 , the filter module  550  and at least one of a sub PCB  590  and a main PCB  595  that are described below. 
     Together with the rear surface cover  580 , the rear surface panel  570  is disposed at the rearmost side of the case  520  and forms the exterior of the rear surface of the portable air purifier  50 . The rear surface panel  570  is disposed behind the filter module  560 . External air is suctioned into the portable air purifier  50  through the rear surface panel  570 . To this end, the rear surface panel  570  has a plurality of first inlets  570   a , thereon. 
     Additionally, together with the rear surface panel  570 , the rear surface cover  580  is disposed at the rearmost side of the case  520  and forms the exterior of the rear surface of the portable air purifier  50 . The rear surface cover  580  is disposed behind the battery  560 . In the embodiment, the area behind the filter module  550  is covered by the rear surface panel  570 . The area behind the battery  560  is covered by the rear surface cover  580 . 
     The rear surface cover  580  may have a second inlet  580   a . The second inlet  580   a  is formed in a way that penetrates on the rear surface cover  580 . The second inlet  580   a  forms a passage connecting among the rear of the case  520 , the battery  560  and a sensor module  600 . Through the second inlet  580   a , external air may flow to the battery  560  and the sensor module  600  in a second area B. 
     Structure of Case 
       FIG.  5    is a front perspective view separately showing a case in  FIG.  1   , and  FIG.  6    is a rear perspective view separately showing the case in  FIG.  1   . 
     Referring to  FIGS.  3 ,  5  and  6   , the portable air purifier  50  includes a case  520  that forms the skeleton of the exterior of the portable air purifier  50 . The case  520  has accommodation space therein, and one side and the other side of the accommodation space in the first direction are open. 
     Directions are defined as follows. A direction from the case  520  to the front surface panel  510  is referred to as a front, and a direction from the case  520  to the rear surface panel  570  is referred to as a rear. At this time, a “first direction” denotes the front-rear direction. A “second direction” is a direction perpendicular to the first direction and denotes the left-right direction. A “third direction” is a direction perpendicular to the first direction and the second direction and denotes the up-down direction. 
     In the embodiment, the case  520  is formed into a cuboid having the front surface and the rear surface that are open, and therein, has accommodation space having the front and the rear that are open. The case  520  may be made of a metallic material. In the embodiment, the case  520  is made of a material such as aluminum that is lightweight and has high strength, for example. 
     The rear surface of the case  520  is open to suction external air. The front surface of the case  520  is open to discharge air purified in the accommodation space of the case  520 . Through the open front surface and the open rear surface of the case  520 , various types of components constituting the portable air purifier  50  may be installed in the accommodation space of the case  520 . 
     A filter module  550  may be mounted in the case  520  or detached from the case  520  through the open rear surface of the case  520 . The rear surface panel  570  is coupled to the open rear surface of the case  520 . The rear surface panel  570  coupled to the case  520  covers the open rear surface of the case  520 . 
     The case  520  may include a first surface part  521 , a second surface part  523 , a first connection surface part  525 , a third surface part  527 , and a second connection surface part  529 , while being formed into a cuboid having the front surface and the rear surface that are open. 
     The first surface part  521  forms a surface in a direction that is perpendicular to the second direction perpendicular to the first direction. That is, the first surface part  521  forms a lateral surface of the case  520 . The first surface part  521  is formed into a vertical flat surface that forms a wall covering a lateral portion of the accommodation space in the case  520 . 
     The case  520  has a pair of first surface parts  521 , and the first surface parts  521  face each other and are spaced a predetermined distance apart from each other. At this time, the pair of first surface parts  521  is disposed in the second direction, i.e., a direction in which the first surface parts  521  are disposed side by side in the left-right direction. 
     The second surface part  523  forms a surface in a direction that is perpendicular to the third direction and is disposed at one side of the pair of first surface parts  521  in the third direction. That is, the second surface part  523  is disposed in the upper portion of the first surface part  521 , and forms a flat surface in a direction parallel with the direction in which the first surface parts  521  are spaced, i.e., a horizontal flat surface. The second surface part  523  forms the upper surface of the case  520 . 
     The first connection surface part  525  is disposed between the first surface part  521  and the second surface part  523 . The first connection surface part  525  is disposed respectively between the end portion of one side of the second surface part  523  and the first surface part  521  below the end portion of one side of the second surface part  523 , and between the end portion of the other side of the second surface part  523  and the first surface part  521  below the end portion of the other side of the second surface part  523 . 
     Each of the first connection surface parts  525  connects the first surface part  521  and the second surface part  523  in a rounded manner. The first connection surface part  525  makes an upper edge of the case  520 , at which the first surface part  521  and the second surface part  523  connect, round, improving the safety of a product and the aesthetic qualities of the exterior of a product. 
     The third surface part  527  is disposed below the second surface part  523  and the first surface part  521 , and forms a flat surface parallel with the second surface part  523 . The third surface part  527  forms the lower surface of the case  520 . Additionally, the third surface part  527  is a portion that supports the portable air purifier  50  such that the portable air purifier  50  keeps standing. 
     The second connection surface part  529  is disposed between the first surface part  521  and the third surface part  527 . The second connection surface part  529  is disposed respectively between the end portion of one side of the third surface part  527  and the first surface part  521  over the end portion of one side of the third surface part  527 , and between the end portion of the other side of the third surface part  527  and the first surface part  521  over the end portion of the other side of the third surface part  527 . 
     Each of the first connection surface parts  525  connects the first surface part  521  and the second surface part  523  in a rounded manner. The first connection surface part  525  makes an upper edge of the case  520 , at which the first surface part  521  and the third surface part  527  connect, round, improving the safety of a product and the aesthetic qualities of the exterior of a product. 
     The case  520  may have a power button  592  in the upper portion thereof, i.e., in the second surface part  523  of the case  520 . The power button  592  is provided as a manipulation button for turning on/off the portable air purifier  50 . 
     Additionally, the case  520  may have an air volume control button  593 , in the upper portion thereof. The air volume control button  593  is provided as a manipulation button for increasing or decreasing the air volume of the portable air purifier  50 . The air volume control button  593  may be disposed near the power button  592  such that the user identifies and manipulates the air volume control button  593  readily. 
     Further, the case  520  may have a strap mounting part  505  for coupling the strap  501  to the case  520 . The strap  501  is provided to allow the user to hold the case  520 . The user can move up the portable air purifier  50  by holding the strap  501  without directly holding the portable air purifier  50 . That is, the strap  501  helps to improve the portability of the portable air purifier  50 . 
     The accommodation space in the case  520  may be divided into a first area A and a second area B. When the accommodation space is divided in the up-down direction, the upper area is the first area A, and an area under the first area A is the second area B. The first area A and the second area B are divided conceptually rather than physically. 
     In the embodiment, among the components accommodated in the accommodation space, the fan modules  540 ,  545  and the filter module  550  are disposed in the first area A, and the battery  550  is disposed in the second area B. 
     Disposition Structure of Components of Portable Air Purifier 
     Referring to  FIGS.  1  to  4   , the accommodation space in the case  520  forming the skeleton of the portable air purifier  50  is divided into a first area A in the upper portion of the case  520  and a second area B in the lower portion of the case  520 . 
     Components in relation to the suction, purification and discharge of air are disposed in the first area A. That is, the filter module  550  and the fan module  540 ,  545  are disposed in the first area A, and accordingly, air flows in the first area A. A plurality of first inlets  570   a  is provided as a passage for suctioning air, on the rear surface panel  570 . An air discharge part  532 ,  533  and an outlet  510   a  are provided as a passage for discharging air purified in the first area A, on the fan cover  530  and the front surface panel  510 . Additionally, a flow path connecting among the first inlet  570   a , the air discharge part  532 ,  533  and the outlet  510   a  is formed in the first area A. 
     That is, the first inlet  570   a , the filter module  550 , the fan module  540 ,  545 , the air discharge part  532 ,  533  and the outlet  510   a  are provided in the first area A, and a flow path for allowing air suctioned into the portable air purifier  50  to pass through the air purifier  50  is formed in the first area A. 
     Components that do not directly relate to an air flow for air purification are disposed in the second area B. That is, the main PCR  595 , the battery  560  and the sensor module  600  are disposed in the second area B. The rear cover  580  covers the open rear of the space where the above components are disposed. 
     In the embodiment, the case  520  is formed in to a cuboid having a length in the up-down direction greater than a length in the lateral direction. Additionally, the up-to-down length of the first area A in the upper portion of the case  520  is greater than that of the second area B in the lower portion of the case  520 . That is, when the portable air purifier  50  stands vertically, the first area A in the upper portion of the case  520  occupies more space than the second area B in the lower portion of the case  520 . 
     A lower cover part  535  of the fan cover  530  is disposed at the frontmost side of the second area B. The battery  560  is disposed behind the lower cover part  535  while being disposed in the second area B. The fan module  540 ,  545  and the filter module  550  are disposed over the battery  560 , and the rear surface cover  580  is disposed behind the battery  560 . Additionally, the sensor module  600  may be disposed between the battery  560  and the rear surface cover  580 . 
     That is, the upper boundary of the battery  560  is defined by the fan module  540 ,  545  and the filter module  550 , the lateral and lower boundaries of the battery  560  are defined by the first surface part  521  and the third surface part  527  of the case  520 , and the rear boundary of the battery  560  is accommodated in space defined by the rear surface cover  580 . 
     In the embodiment, the battery  560  is a heavier object than the fan module  540 ,  545  and the filter module  550 . It is preferable that the battery  560  weights more than a total weigh of the fan module  540 ,  545  and the filter module  550 . 
     Ordinarily, since the weight per unit volume of the battery  560  is much greater than that of the fan module  540 ,  545  and that of the filter module  550 , the battery  560  may be readily provided as a heavier object than the fan module  540 ,  545  and the filter module  550  although the weight or size of the battery  560  does not increase intentionally. 
     That is, even if a battery  560  having capacity required for the ordinary use of an portable air purifier  50  is applied to the portable air purifier  50 , naturally, the battery  560  weights more than the fan module  540 ,  545  and the filter module  550 . 
     When the battery  560  as a heavy object is disposed in the lower portion of the portable air purifier  50 , the following effects can be produced. 
     First, when the battery  560  that is a heavy object is disposed in the lower portion of the portable air purifier  50 , the center of gravity of the portable air purifier  50  is biased toward the lower side of the portable air purifier  50  from the up-to-down center of the portable air purifier  50 . That is, the center of gravity of the portable air purifier  50  is biased toward the lower side of the portable air purifier  50 , in which the battery  560  is disposed. 
     The bias of the center of gravity of the portable air purifier  50  toward the lower portion of the portable air purifier  50 , where the battery  560  is disposed, reduces the risk of the overturning of the portable air purifier  50 , when the portable air purifier  50  stands vertically. 
     That is, when the portable air purifier  50  stands vertically, the portable air purifier  50  rarely falls since the center of gravity of the portable air purifier  50  is at the lower side of the portable air purifier  50  because of the battery  560  in the lower portion of the portable air purifier  50 . 
     When it comes to the portable air purifier  50  in the embodiment, the third surface part  527  of the case  520  forms a flat surface having a greater surface area than the second surface part  523  of the case  520 . That is, the third surface part  527  forms a long flat surface that has a greater length in the lateral direction than the second surface part  523 . That is, under the assumption that the length of the third surface part  527  in the lateral direction is d1 and that the length of the upper surface part  527  in the lateral direction is d2, the relationship d1&gt;d1 is satisfied. Additionally, the second connection surface part  529  connecting the third surface part  527  and the first surface part  521  forms a curved surface that has a less R value than the first connection surface part  525 . 
     The third surface part  527  of the case  520  is a portion contacting the bottom surface of the portable air purifier  50  when the portable air purifier  50  stands vertically. That is, the third surface part  527  is a portion that supports the portable air purifier  50  such that the portable air purifier  50  keeps sanding. 
     Since the third surface part  527  of the case  520  forms a surface area that has a greater surface area than the second surface part  523 , the third surface part  527  of the case  520  can support the portable air purifier  50  that stands vertically, more reliably. 
     In combination of the structure in which the battery  560  is disposed in the lower portion of the portable air purifier  50  such that the center of gravity of the portable air purifier  50  is at the lower side of the portable air purifier  50 , and the structure in which the third surface part  527  of the case  520 , which supports the portable air purifier  50  standing vertically, forms a flat surface that has a greater surface area than the second surface area  523 , effectively suppressing the overtraining of the portable air purifier  50  and reliably keeping the portable air purifier  50  standing vertically. 
     Second, when the battery  560  as a heavy object is disposed in the lower portion of the portable air purifier  50 , the other components such as the filter module  550  and the fan module  540 ,  545  constituting the portable air purifier  50  need to be disposed further upward than the battery  560 . That is, components in relation to the suction, purification and discharge of air need to be disposed further upward than the battery  560 . 
     To ensure the charge capacity of the battery  560 , required for the smooth operation of the portable air purifier  50 , the battery  560  needs to have a predetermined size or greater. It means that the portable air purifier  50  needs to have installation space of a predetermined size or greater, therein, to install the battery  560 . Additionally, it is irrational to form a flow path for allowing an air to flow in the space where the battery  560  is installed. Accordingly, components in relation to the suction, purification and discharge of air needs to be disposed to avoid the battery  560 , i.e., in a position higher than the position of the battery  560 . 
     In the disposition structure, a flow path for the suction, purification and discharge of air is formed in the first area A higher than the position of the battery  560 , in the portable air purifier  50 . Thus, the suction of air into the portable air purifier  50 , and the discharge of air purified in the portable air purifier  50  are performed in a position higher than the position of the battery  560 . 
     As purified air is discharged from the upper portion of the portable air purifier  50 , the air purified in the portable air purifier  50  can reach the user’s face more easily. 
     When the portable air purifier  50  is placed and used on the bottom surface lower than the user’s face, the portable air purifier  50  that stands vertically allows a greater amount of air purified in the portable air purifier  50  to reach the user’s face than the portable air purifier  50  that lies horizontally. 
     To this end, when purified air is discharged from the upper portion of the portable air purifier  50  in the state in which the portable air purifier  50  stands vertically, a greater amount of the air purified in the portable air purifier  50  reaches the user’s face. 
     In the embodiment, since the battery  560  is disposed in the lower portion of the portable air purifier  50 , a flow path for the suction, purification and discharge of air is formed in a position higher than the position of the battery  560 , in the portable air purifier  50 . Accordingly, purified air is discharged from the upper portion of the portable air purifier  50 , and a greater amount of the air purified in the portable air purifier  50  reaches the user’s face. 
     That is, in the structure where the battery  560  is disposed in the lower portion of the portable air purifier  50 , the structural stability of the portable air purifier  50  can improve to reduce the risk of overturning of the portable air purifier  50  that stands vertically, and an efficient flow path can also be formed to enable a greater amount of air purified in the portable air purifier  50  to reach the user’s face. 
     Third, the structure, in which the battery  560  as a heavy object is disposed in the lower portion of the portable air purifier  50  such that components in relation to the suction, purification and discharge of air are disposed in a position higher than the position of the battery  560 , may help to expand the range in which the portable air purifier  50  is installed. 
     In an example, when the portable air purifier  50  is used in the state of being held in a cup holder h in a vehicle, the area where air is suctioned and the area where purified air is discharged are disposed higher than the cup holder, such that the portable air purifier  50  is reliably held in vehicle while maintaining a high level of air purification performance. To this end, the up-to-down length of the second area B where the battery  560  is disposed is set to the depth of the cup holder or greater, for example. 
     In another example, if the lower area of the portable air purifier  50  is fixed by a tong type holder and the like, the portable air purifier  50  can be fixed stably while the portable air purifier 50’s areas where air is suctioned and discharged are not blocked. 
     That is, components such as a battery  560  that does not directly relate to an air flow for air purification are disposed in the lower portion of the portable air purifier  50 , and the portable air purifier  50  is held and fixed through its lower portion, ensuring a high level of air purification performance and a reliable fixation of the portable air purifier  50 . 
     Disposition Structure of Fan Module and Filter Module 
     The portable air purifier  50  in the embodiment may include a fan module  540 ,  545  that suctions air from the rear of the portable air purifier  50  and discharges air through the front of the portable air purifier  50 . 
     The fan module  540 ,  545  may be disposed between the fan cover  530  and the filter module  550 . That is, the fan cover  530  may be disposed at the front of the fan module  540 ,  545 , and the filter module  550  may be disposed at the rear of the fan module  540 ,  545 . 
     While the fan module  540 ,  545  is accommodated in the accommodation space of the case  520 , the fan module  540 ,  545  may be disposed in the first area A. Accordingly, the fan module  540 ,  545  may be disposed in a position that faces the rear surface of the upper cover part  531 , out of the upper cover part  531  of the fan cover  530  and the lower cover part  535  of the fan cover  530 . 
     In the embodiment, the portable air purifier  50  is provided with two fan modules  540 ,  545 , for example. At this time, the portable air purifier  50  is provided with a first fan module  540  and a second fan module  545 . 
     The first fan module  540  may be disposed between the discharge surface and the filter module  550 , specifically, between the fan cover  530  and the filter module  550 . At this time, the first fan module  540  may be disposed in parallel with the suction surface and the discharge surface. The second fan module  545  and the first fan module  540  may be disposed on the same surface. That is, the second fan module  545  may be disposed in parallel with the suction surface and the discharge surface, between the fan cover  530  and the filter module  550 . 
     The positions of the first fan module  540  and the second fan module  545  are disposed not to overlap each other in the third direction. To this end, the first fan module  540  and the second fan module  545  may be disposed in the third direction, i.e., in the up-down direction. That is, the first fan module  540  and the second fan module  545  may be disposed on the same perpendicular line. 
     The first fan module  540  and the second fan module  545  may be disposed to face the air discharge part  532 ,  533  formed on the fan cover  530 . Accordingly, air, suctioned into the first fan module  540  and the second fan module  545  through the rear surface panel  570 , may pass through an upper air discharge part  532  and a lower air discharge part  533  respectively, and then be discharge forward through the front surface panel  510 . 
     In the embodiment, the first fan module  540  and the second fan module  545  may have the same size and shape, for example. However, the first fan module  540  and the second fan module  545  may have a different size and shape. 
     The filter module  550  may be disposed between the suction surface and the fan module  540 ,  545 . The filter module  550  includes a filter  559 , and the filter  559  filters air suctioned through the suction surface. 
     The filter  559  may form a filter surface that forms a flat surface in a direction orthogonal to the directions in which the fan suctions and discharges air. That is, the filter  559  may form a filter surface parallel with the suction surface and the discharge surface. The suction surface, the filter surface of the filter  599  and the discharge surface may be disposed in a straight line. 
     Additionally, the filter  559  may form a filter surface parallel with the fan module  540 ,  545 . The suction surface, the filter surface, the fan module  540 ,  545  and the discharge surface may be disposed in a straight line. 
     The positions of the first fan module  540  and the second fan module  545  in the first direction and the second direction may correspond to the area occupied by the filter surface. Further, the surface areas taken up by the first fan module  540  and the second fan module  545  may correspond to the surface area of the filter surface. For example, when viewed from the front, the first fan module  540  and the second fan module  545  may be disposed to overlap the filter surface. 
     Furthermore, the directions of the first fan module  540  and the second fan module 545’s suction of air may be the same as the directions of the suction surface and the discharge surface’s disposition. That is, the first fan module  540  and the second fan module  545  may suction air respectively in the first direction or the axial direction. 
     The surface area occupied by the fan module  540 ,  545  including the first fan module  540  and the second fan module  545  described above may correspond to the surface area of the suction surface and the surface area of the filter surface. Additionally, the surface area taken by the fan module  540 ,  545  may correspond to the surface area of the discharge surface. Under the assumption that the suction surface, the filter surface and the discharge surface have a corresponding surface area, the surface area occupied by the fan module  540 ,  545  may correspond to the surface area of each of the suction surface, filter surface and discharge surface. 
     Accordingly, air can be suctioned and discharged by the fan module  540 ,  545  through the entire suction surface and the entire discharge surface. 
     For example, air can be suctioned by the fan module  540 ,  545  through the suction surface that is ensured as much surface area as the fan module  540 ,  545 . Air suctioned through the suction surface can be filtered by the filter surface that is ensured as much surface area as the suction surface and the fan module  540 ,  545 . Additionally, air can be discharged by the fan module  540 ,  545  through the discharge surface that is ensured as much surface area as the fan module  540 ,  545 . 
     That is, the suction surface and the discharge surface may ensure a passage having an optimal surface area required for the fan module  540 ,  545  to suction and discharge air. Additionally, the filter  559  may ensure a filter surface having an optimal surface area required to filter air suctioned through the suction surface. Thus, air may flow effectively, based on the operation of the fan module  540 ,  545 . 
     In the embodiment, the suction surface, the filter surface, the fan module  540 ,  545  and the discharge surface are disposed in parallel. Additionally, the suction surface, the filter surface, the fan module  540 ,  545  and the discharge surface are disposed in the first direction, and air flows in the same direction. That is, air, flowing based on the operation of the fan module  540 ,  545 , can flow, in the same straight line, in the same direction as the direction in which the suction surface, the filter surface, the fan module  540 ,  545  and the discharge surface are disposed. 
     As air flows in a straight line, resistance against the flow of the air decreases, and the air can flow more smoothly. Accordingly, a sufficient amount of air is suctioned, and in response, a sufficient amount of air is discharged by the fan module  540 ,  545 , leading to improvement in the air purification performance of the portable air purifier  50 . 
     Structure of Fan Module 
     As described above, the portable air purifier  50  in the embodiment may include a plurality of fan modules  540 ,  545 . In the embodiment, the portable air purifier  50  includes the first fan module  540  and the second fan module  545 , and the first fan module  540  and the second fan module  545  have the same structure, for example. Herein, the structure of the first fan module  540  is described as an example. 
       FIG.  7    is a cross-sectional view specifically showing the structure of portion “VII” in  FIG.  4   ,  FIG.  8    is a perspective view separately showing a fan module of one embodiment, and  FIG.  9    is an perspective view separately showing a fan case in  FIG.  8   .  FIG.  10    is a front view separately showing a fan in  FIG.  8   ,  FIG.  11    is a side view showing the fan in  FIG.  10   , and  FIG.  12    is a cross-sectional view along line “X II - X II” in  FIG.  11   . 
     In  FIG.  7   , some components of the portable air purifier are omitted. 
     Referring to  FIGS.  3 ,  4 ,  7  and  8   , the first fan module  540  may include a shaft  5410 , a motor  5420 , a fan case  5430  and a fan  5440 . 
     The shaft  5410  may extend in the first direction, i.e., the axial direction. One side of the shaft  5410  in the axial direction may be connected to the fan  5450 . The other side of the shaft  5410  in the axial direction may be connected to the fan case  5430 . Detailed description in relation to this is provided below. 
     The motor  5420  connects to the fan  5450  and applies a rotational force to the fan  5450 . For example, the motor  5420  may be provided in the form of a BLDC motor in which a frequency can be adjusted. The motor  5420  may include a stator  5421  and a rotor  5423 . 
     The stator  5421  may be disposed at the center side of the motor  5420  in the radial direction of the motor  5420 , and the rotor  5423  may be disposed outside the stator  5421  in the radial direction of the stator  5421 . That is, the motor  5420  in the embodiment may be provided in the form of an outer motor. 
     The stator  5421  may be fixed to the fan case  5430 ,  5440 . The rotor  5423  may be fixed to the fan  5450 . The rotor  5423  may rotate around the shaft  5410 , outside the stator  5421 , and the fan  5450  may rotate together with the rotor  5423  as the rotor  5423  rotates. 
     The fan case  5430 ,  5440  may support the stator  5421  and the shaft. The fan case  5430 ,  5440  may include a first support part  5430  and a second support part  5440 , as illustrated in  FIGS.  7  to  9   . 
     The first support part  5430  may be disposed at the center side of the fan case  5430 ,  5440  in the radial direction of the fan case  5430 ,  5440 . The first support part  5430  may include a support plate  5431  and a boss  5433 . 
     The support plate  5431  may be formed into a circular plate. The support plate  5431  may form a flat surface that is parallel with at least any one of the suction surface, the filter surface and the discharge surface. The boss  5433  may protrude in the axial direction toward the fan  5450  from the support plate  5431 . In the embodiment, the boss  5433  is disposed at the center of the support plate  5431  in the radial direction of the support plate  5431 , for example. 
     The stator  5421  may be installed in the first support part  5430 . The stator  5421  may be coupled to the boss  5433  while surrounding the boss  5433  from the outside in the radial direction. That is, the stator  5421  and the boss  5433  may be coupled in a way that the boss  5433  is fitted into the stator  5421  in the axial direction. The support plate  5431  may support the boss  5433  coupled to the stator  5421  at one side of the boss  5433  in the lateral direction, as described above. 
     Additionally, one side of the stator  5421  coupled to the boss  5433  in the axial direction of the stator  5421  may face the support plate  5431 . While one side of the stator  5421  in the axial direction of the stator  5421  contacts the support plate  5431 , the stator  5421  and the support plate  5431  may be coupled. Certainly, the stator  5421  may be installed in the first support part  5430  in a way that the stator  5421  is spaced from the support plate  5431 . 
     Further, the boss  5433  may have a hollow hole, therein. The shaft  5410  may be inserted into the boss  5433  through the hollow hole. The shaft  5410  may pass through the boss  5433  in the axial direction and protrude from the boss  5433 , and may be connected to a below-described hub  5451  of the fan  5450 , outside the boss  5433 . 
     A bearing  5435  may be inserted into the boss  5433  having the hollow hole. The shaft  5410  may be coupled to the bearing  5435 , in the boss  5433 . Accordingly, the shaft  5410  may be rotatably supported by the bearing  5435 . In the embodiment, a pair of bearings  5435  is spaced a predetermined distance apart from each other in the axial direction, for example. The bearing  5435 , disposed as described above, may help to install the shaft  5410  rotatably in the boss  5433  in a more reliable manner. 
     The second support part  5440  may support the first support part  5430 , and couple the first fan module  540  to at least any one of the fan cover  530  and the filter module  550 . 
     The second support part  5440  may be disposed outside the first support part  5430  in the radial direction of the first support part  5430 . The second support part  5440  may support the first support part while surrounding the first support part  5430  from the outside in the radial direction. 
     The second support part  5440  may be formed into an approximate rectangle. For example, the length of the second support part  5440  in the second direction may be determined to correspond to the length of the filter module  550  in the second direction. Additionally, the length of the second support part  5440  in the third direction may be determined to correspond to half the length of the filter module  550  in the third direction. That is, if a pair of second support parts  5440  is disposed in the third direction, the exterior shapes of the pair of second support parts  5440  and the filter module  550  may be approximately aligned, when viewed from the front. 
     The second support part  5440  may have a hollow hole, therein. The hollow hole of the second support part  5440  may be formed in a way that the hollow hole penetrates the inside of the second support part  5440  in the axial direction. The hollow hole may have a radius greater than a radius of the support plate  5431 . That is, a hollow hole bigger than the support plate  5431  is formed in the second support part  5440 , and the support plate  5431  may be disposed in the second support part  5440 . 
     Accordingly, the second support part  5440  may be spaced a predetermined distance apart from the first support part  5430 , specifically, from the support plate  5431  in the centrifugal direction. 
     A fan outlet  5430   a  may be formed between the support plate  5431  and the second support part  5440  that are spaced as described above. The fan outlet  5430   a  may form a passage allowing air being introduced into the first fan module  540  to pass through the first fan module  540  and escape from the first fan module  540 . 
     The fan case  5430 ,  5440  may further include a connection part  5445 . The connection part  5445  may extend from the support plate  5431  in the centrifugal direction and may be connected to the second support part  5440 . The connection part  5445  may connect the support plate  5431  and the second support part  5440  and help the second support part  5440  to support the support plate  5431 . 
     In the embodiment, a plurality of connection parts  5445  may be disposed between the support plate  5431  and the second support part  5440 . Additionally, each of the connection parts  5445  may have a width less than the length of the connection part  5445  in the radial direction. Each of the connection parts  5445 , formed as described above, may be spaced at a predetermined interval along the circumferential direction of the support plate  5431 . 
     Accordingly, while the fan outlet  5430   a  is formed between the support plate  5431  and the second support part  5440 , the fan outlet  5430   a  may be respectively formed among the plurality of connection parts  5445 . 
     Additionally, the connection part  5445  may provide a passage through which an electric wire, connected to the stator  5421  on the support plate  5431 , passes. The electric wire connecting to the stator  5421  may be withdrawn toward the second support part  5440  side through the area where the connection part  5445  is disposed. At this time, the electric wire may pass through the fan outlet  5430   a  area in the state being covered by the connection part  5445 , and connect the stator  5421  and the main PCB  595  (see  FIG.  3   ). When viewed from the front, the electric wire that is withdrawn from the stator  5421  and passes through the fan outlet  5430   a  area is cover by the connection part  5445  and is not be seen. 
     The second support part  5440  may be provided with a side rib  5443 . The side rib  5443  may be disposed at at least any one of both sides of the second support part  5440  in the second direction of the second support part  5440 . The side rib  5443  may protrude from a lateral portion of the second support part  5440  in the second direction of the second support part  5440 . 
     The length of the side rib  5443  in the second direction may be set to correspond to the length of the second support part  5440  in the second direction. Additionally, the length of the side rib  5443  in the first direction may be less than the length of the first support part  5430  in the first direction. That is, the side rib  5443  may have a thickness less than that of the first support part  5430 . For example, the side rib  5443  may have a thickness that is one fourth or less of the thickness of the first support part  5430 . 
     The side rib  5443  may be biased toward the front or the rear of the second support part  5440  while protruding from the second support part  5440 . In the embodiment, the side rib  5443  is biased toward the rear of the second support part  5440 , for example. 
     As the fan module  540 ,  545  is inserted into the case  520 , the side rib  5443  may contact both lateral surfaces of the case  520 , i.e., the inner surfaces of the first surface parts  521 . Accordingly, predetermined space may be formed between a lateral surface of the second support part  5440  and the first surface part  521 . 
     The formed space may be used as space for allowing an electric wire to pass. For example, an electric wire connecting to the sub PCB  595  disposed on the fan module  540 ,  545  may pass through the space and may be connected to the stator  5421  of the motor  5420 . 
     Referring to  FIGS.  7  and  10  to  12   , the fan  5450  may include a hub  5451  and fan blade  5455 . 
     The hub  5451  is disposed at the center of the fan  5450  in the radial direction of the fan  5450 , and rotates together with the rotor  5423  and the shaft. The hub  5451  may include a first fan module  540 ,  545  and a skirt part  5433 . 
     The first fan module  540 ,  545  may be formed into a circular plate parallel with the support plate  5431 . The first fan modules  540 ,  545  may be disposed in parallel with the support plate  5431  with the boss  5433  between the first fan modules  540 ,  545 . 
     The first fan module  540 ,  545  may be provided with a shaft coupling part  5452   a . The shaft coupling part  5452   a  may be disposed at the center of the first fan module  540 ,  545  in the radial direction of the first fan module  540 ,  545 . The shaft coupling part  5452   a  may protrude in the axial direction toward the boss  5433  from the first fan module  540 ,  545 . 
     The shaft coupling part  5452   a  may be coupled to the end portion of the shaft  5410  in the axial direction of the shaft  5410 . For example, the shaft coupling part  5452   a  may be coupled to the shaft  5410  in a way that the shaft  5410  is fitted into the shaft coupling part  5452   a . The shaft  5410  may be fixed to the shaft coupling part  5452   a  or rotatably coupled to the shaft coupling part  5452   a . 
     The skirt part  5453  may protrude toward the support plate  5431  from the edge of the hub plate part  5452 . The skirt part  5453  may form a slant surface that inclines in the centrifugal direction as the skirt part  5452  becomes farther from the hub plate part  5452  in the axial direction. For example, the shape in which the hub plate part  5452  and the skirt part  5453  connect may be a truncated cone shape which has a hollow hole therein and one side of which is open. The skirt part  5433  may be disposed outside the stator  5421  in the radial direction of the stator  5421 . That is, the stator  5421  may be disposed in space surrounded by the skirt part  5453  and the hub plate part  5452 . 
     The fan blade  5455  may protrude from the hub  5451  in the centrifugal direction. The fan  5450  may be provided with a plurality of fan blades  5455 , and the fan blades  5455  may be spaced a predetermined distance apart from one another along the circumference direction of the hub  5451 . 
     Specifically, the fan blade  5455  may protrude from the skirt part  5453  in the centrifugal direction. At this time, the inside of the fan blade  5455  in the radial direction thereof may be connected to the skirt part  5453 , and the outside of the fan blade  5455  in the radial direction thereof may be connected to a shroud  5457  that is described hererafter. That is, the skirt part  5453  is a portion of the hub  5451 , which directly connects to the fan blade  5455  and directly contacts air passing through the first fan module  540 . The skirt part  5453  may closely relate to a flow path of air passing through the first fan module  540 . 
     The fan  5450  may further include a shroud  5457 . The shroud  5457  may be spaced a predetermined distance apart from the hub  5451  in the radial direction, outside the hub  5451  in the radial direction thereof. The shroud  5457  may be spaced from the hub  5451  by a distance corresponding to the length of the fan blade  5455  in the radial direction of the fan blade  5455 . Additionally, each of the fan blades  5455  may connect the hub  5451 , specifically, the skirt part  5453 , and the shroud  5457 . 
     The shroud  5457  may form a slant surface that inclines in the centripetal direction as the shroud  5457  becomes farther from the fan case  5430 ,  5440  in the axial direction, i.e., toward the rear. For example, the shroud  5457  may form a slant surface that is approximately parallel with the skirt part  5453 . In the embodiment, a gap between the skirt part  5453  and the shroud  5457  increases further toward the front, for example. 
     Each of the fan blades  5455 , connecting the shroud  5457  and the skirt part  5433 , may include a leading edge  5455   a , a trailing edge  5455   b , a shroud chord  5455   c  and a hub chord  5455   d . 
     The leading edge  5455   a  may be disposed at the front end of the fan  5450  in a rotation direction and formed to be straight. The rotation direction is defined as a direction in which the fan  5450  rotates. The leading edge  5455   a  may be formed as a straight line that is disposed at the front end of the fan  5450  in the rotation direction of the fan  5450  and extends in the radial direction. 
     The trailing edge  5455   b  may be disposed at the rear end of the fan in the rotation direction and formed to be straight. The trailing edge  5455   b  may be formed as a straight line that extends in a direction between the axial direction and the radial direction. 
     The shroud chord  5455   c  may connect one end of the leading edge  5455   a  and one end of the trailing edge  5455   b . The shroud chord  5455   c  may extend from the inner circumferential surface of the shroud  5457 . 
     The hub chord  5455   d  may connect the other end of the leading edge  5455   a  and the other end of the trailing edge  5455   b . The hub chord  5455   d  may extend from the outer circumferential surface of the hub  5451 . 
     Additionally, one end of the leading edge  5455   a  and one end of the trailing edge  5455   b  may be connected to the inner circumferential surface of the shroud  5457 . The other end of the leading edge  5455   a  and the other end of the trailing edge  5455   b  may be connected to the outer circumferential surface of the skirt part  5453 . 
     One end of the leading edge  5455   a  may be disposed closer to the center of the hub plate part  5452  in the radial direction of the hub plate part  5452  than one end of the trailing edge  5455   b . The other end of the leading edge  5455   a  may be disposed closer to the center of the hub plate part  5452  in the radial direction of the hub plate part  5452  than the other end of the trailing edge  5455   b , since one end and the other end of the leading edge  5455   a  is disposed further forward than one end and the other end of the trailing edge  5455   b  in the rotation direction, and the radius of the skirt part  5453  decreases further toward the front in the rotation direction. 
     Additionally, the hub  5451  may include an inner projection part  5454 . The inner projection part  5454  may protrude toward the support plate  5431  from the hub plate part  5452 . In the embodiment, the inner projection part  5454  and the skirt part  5453  protrude from the same point on the hub plate part  5452 , e. g. , from the edge of the hub plate part  5452 , for example. 
     The inner projection part  5454  may be formed in a way that the inner projection part  5454  extends from the hub plate part  5452  in the axial direction. For example, the shape in which the hub plate part  5452  and the skirt part  5453  connect may be a cylinder shape which has a hollow hole therein and one side of which is open. 
     The inner projection part  5454  may be disposed between the skirt part  5453  and the stator  5421 . That is, the stator  5421  may be disposed in space surrounded by the inner projection part  5454  and the hub plate part  5452 . 
     The rotor  5423  may be disposed between the inner projection part  5454  and the stator  5421 . The rotor  5423  may be fixed onto the inner circumferential surface of the inner projection part  5454 . That is, the stator  5421  may be fixed to the fan case  5430 ,  5440 , and the rotor  5423  may be fixed to the fan  5450 . Accordingly, the fan  5450  may rotate together with the rotor  5423  as the rotor  5423  rotates. 
     In the embodiment, the fan blade  5455  may be connected to the skirt part  5453  of the hub  5451 . To induce the flow of air flowing into the fan module  540 ,  545  in a direction between the axial direction and the radial direction, the skirt part  5453  forms a slant surface that inclines in a direction between the axial direction and the radial direction. 
     Since the skirt part  5453  is obliquely formed, it is difficult to fix the rotor  5423  to the inner circumferential surface of the skirt part  5453 . For example, for the rotor  5423  to be fixed to the inner circumferential surface of the skirt part  5453 , the rotor  5423  needs to be entirely formed into an approximate truncated cone having a hollow hole since the shape of the outer circumferential surface of the rotor  5423  needs to correspond to the shape of the inner circumferential surface of the skirt part  5453 . However, the shape of the rotor  5423  may be inappropriate for the reliable driving of the motor  5420 . 
     In consideration of the fact, in the embodiment, the inner projection part  5454  is provided between the skirt part  5453  and the stator  5421 . The inner projection part  5454  may provide a fixation surface that allows the rotor  5423  to be fixed stably to the inside of the hub  5451  when the rotor  5423  is entirely formed into a cylinder having a hollow hole. 
     Additionally, the inner projection part  5454  may form a structure for improving the rigidity of the hub  5451 , in the hub  5451 . The inner projection part  5454  may help to improve the rigidity of the entire fan  5450  effectively while suppressing a significant increase in the weight of the entire fan  5450 . 
     Structure of Coupling Between Fan Module and Fan Cover 
       FIG.  13    is an exploded perspective view separately showing a fan cover and a fan module. 
     Referring to  FIG.  13   , the fan cover  530  may include an upper cover part  531  and a lower cover part  535 . 
     The upper cover part  531  is disposed at the front of the fan module  540 ,  545 . The upper cover part  531  may be provided with an air discharge part  532 ,  533 . The air discharge part  532 ,  533  may be formed in a way that a portion of the upper cover part  531  penetrates or is cut. The air discharge part  532 ,  533  may form a passage that connects the front of the case  520 , i.e., the discharge surface, and the fan  5450  of the fan module  540 ,  545 , on the fan cover  530 . 
     In the embodiment, the portable air purifier  50  is provided with two fan modules  540 ,  545 , for example. That is, the first fan module  540  and the second fan module  545  are disposed vertically in the accommodation space of the case  520 . 
     Accordingly, the fan cover  530  may also be provided with two air discharge parts  532 ,  533 . That is, an upper air discharge part  532  and a lower air discharge part  533  may be disposed vertically at the upper cover part  531 . 
     Air having passed through the first fan module  540  is discharged forward through the upper air discharge part  532 , and air having passed through the second fan module  545  may be discharged forward through the lower air discharge part  533 . 
     In another example, the portable air purifier may be provided with one fan assembly or three or more fan assemblies, and accordingly, the fan cover may be provided with one air discharge part or three or more air discharge parts. 
     Additionally, the upper cover part  531  may be provided with a first fastening projection  534 . The first fastening projection  534  may protrude from the rear surface of the upper cover part  531  rearward. In response, the fan case  5430 ,  5440  may be provided with a fastening hole  5441 . The fastening hole  5441  may be formed in a way that penetrates in the front-rear direction in the second support part  5440 . 
     In an example, a total of four fastening holes  5441  may be provided, and each of the fastening holes  5441  may be disposed at each edge of the second support part  5440 . The first fastening projection  534  may be disposed respectively in positions corresponding to the positions of the fastening holes  5441 . 
     Each of the first fastening projections  534  may be inserted into the fastening hole  5441  and fitted into and coupled to the second support part  5440 . As a result of the coupling between the first fastening projection  534  and the second support part  5440 , the fan cover  530  and the fan module  540 ,  545  may be coupled at a plurality of points. 
     As the fan cover  530  and the fan module  540 ,  545  are coupled, the fan module  540 ,  545  may be fixed to the rear of the fan cover  530 . At this time, the fan module  540 ,  545  may be fixed in the position where the fan outlet  5430   a  formed at the front of the fan module  540 ,  545  overlaps the air discharge part  532 ,  533  formed at the fan cover  530  in the first direction. Thus, a straight line passage may be formed to allow air discharged from the fan module  540 ,  545  to pass through the fan cover  530 . 
     Structure of Fan Base 
       FIG.  14    is an exploded perspective view separately showing a fan module, a fan base and a filter,  FIG.  15    is a rear perspective view showing the rear surface of a fan base, and  FIG.  16    is a perspective view showing a coupling state between the fan base and the filter. 
     Referring to  FIGS.  7  and  13  to  16   , the portable air purifier  50  according to the present disclosure may further include a fan base  5460 . 
     The fan base  5460  may be disposed between the filter module  550  and the fan module  540 ,  545 . The fan base  5460  may be formed into a shape corresponding to the shape of the filter surface. For example, the fan base  5460  may be formed into a shape of the filter  559  viewed from the front, i.e., a rectangular shape. The fan base  5460  may include a base plate  5461 , and a bell mouth  5463 . 
     In this embodiment, two fan bases  5460  disposed in the third direction, i.e., the up-down direction, are disposed between the filter module  550  and the fan module  540 ,  545 , for example. At this time, one fan base  5460  disposed in the upper portion is disposed between the first fan module  540  and the filter module  550 , and the other fan base  5460  disposed in the lower portion is disposed between the second fan module  545  and the filter module  550 . 
     When the fan base  5460  is provided separately depending on the number of the fan modules, the fan base  5460  may be provided in response to the number of the fan modules even if the number of the fan modules varies. That is, when one fan module is provided, one fan base  5460  is applied, and when two or more fan modules are provided, the same number of the fan bases  5460  as the number of the fan modules may be stacked in the up-down direction. Thus, the fan base  5460  is provided regardless of the number of the fan modules, ensuring ease of management of components. 
     Despite the fact, the fan base  5460  may be provided in a way that a single fan base  5460  includes a plurality of fan inlets  5462 . 
     The base plate  5461  may be disposed between the filter module  550  and the fan module  540 ,  545 . The length of the base plate  5461  in the first direction may be much less than that of the filter module  550  and the fan module  540 ,  545 . For example, the base plate  5461  may be formed into a rectangular plate. 
     The base plate  5461  may have a fan inlet  5462 . The fan inlet  5462  may be formed in a way that fan inlet  5462  penetrates on the base plate  5461  in the first direction. The fan inlet  5462  may be disposed approximately in the position where the fan inlet  5462  overlaps the air discharge part  532 ,  533  (see  FIG.  13   ) of the fan cover  530  and the fan outlet  5430   a  of the fan module  540 ,  545  in the first direction. The fan inlet  5462  formed as described above may form a passage that connects the filter  559  and the fan module  540 ,  545 , at the fan base  5460 . 
     The bell mouth  5463  may protrude from the base plate  5461 . The bell mouth  5463  may protrude from the base plate  5461  to the fan module  540 ,  545 , in the axial direction. 
     In the embodiment, the fan inlet  5462  has the same shape as the shroud  5457 , i.e., a circular shape, for example. Additionally, the radius of the fan inlet  5462  may be set similarly to the radius of a portion of the shroud  5457 , which is adjacent to the fan inlet  5462 . 
     The bell mouth  5463  may be formed in a way that the bell mouth  5463  surrounds the outer circumferential surface of the fan inlet  5462  formed as described above. In other words, the fan inlet  5462  may be formed in a way that the fan inlet  5462  penetrates at the inside of the bell mouth  5463  in the radial direction of the bell mouth  5463 . 
     The bell mouth  5463  may protrude toward the fan module  540 ,  545  from the fan inlet  5462  in the first direction. At this time, at least a portion of the bell mouth  5463  may be inserted into the shroud  5457  in the radial direction of the shroud  5457 . The bell mouth  5463  guides a suction flow at the entrance of the fan module  540 ,  545 , and help to improve the suction and discharge performance of the fan module  540 ,  545 . 
     The fan base  5460  may be coupled to the fan base  5460 . To this end, any one of the fan base  5460  and the filter module  550  may have a fastening boss  5433 , and any one of the fan base  5460  and the filter module  550  may have a second fastening projection  553 . In the embodiment, the fan base  5460  has the fastening boss  5433 , and the filter module  550  has the second fastening projection  553 , for example. 
     The fastening boss  5433  may protrude from the base plate  5461  to the filter module  550  in the first direction. The fastening boss  5433  may have a hollow hole. The second fastening projection  553  may protrude from the filter module  550 , specifically, the front surface of the filter case  551 , toward the fan base  5460  in the first direction. The second fastening projection  553  may be fitted into and coupled to the fastening boss  5433  in a way that the second fastening projection  553  is inserted into the hollow hole of the fastening boss  5433 . 
     In an example, a total of four fastening bosses  5433  are provided, and each of the fastening bosses  5433  may be disposed at each edge of the first support part  5430 . The second fastening projection  553  may be disposed respectively in positions corresponding to the positions of the fastening bosses  5433 . 
     Based on the coupling between the second fastening projection  553  and the fastening boss  5433 , the fan base  5460  and the filter module  550  may be coupled at a plurality of points. As the fan base  5460  is coupled to the filter module  550  as described above, the fan base  5460  may be fixed to the front of the filter module  550 . 
     Additionally, the fan base  5460  may be coupled to the fan module  540 ,  545 . To this end, any one of the fan base  5460  and the fan module  540 ,  545  is provided with a third fastening projection  5467 , and the other may be provided with a projection boss  5442 . In the embodiment, the fan base  5460  is provided with the third fastening projection  5467 , and the fan module  540 ,  545  is provided with the projection boss  5442 , for example. 
     The projection boss  5442  may protrude from the second support part  5440  toward the fan base  5460  in the first direction. The projection boss  5442  may have a hollow hole. The third fastening projection  5467  may protrude from the front surface of the base plate  5461  toward the front. The third fastening projection  5467  may be fitted into and coupled to the fastening boss  5433  in a way that the third fastening boss  5467  is inserted into the hollow hole of the projection boss  5442 . 
     As the projection boss  5442  and the third fastening projection  5467  are coupled, the fan base  5460  and the fan module  540 ,  545  may be coupled such that the second support part  5440  is spaced a predetermined distance apart from the base plate  5461 . At this time, the predetermined distance is set to the length of a portion of the fan  5450  in the axial direction, protruding outward in the radial direction of the second support part  5440 , e. g. , the length of the shroud  5457  in the first direction, or greater. 
     Further, a total of four projection bosses  5442  are provided, and each of the projection bosses  5442  may be disposed at each edge of the second support part  5440 . The third fastening projection  5467  may be disposed respectively in positions corresponding to the positions of the projection bosses  5442 . 
     A gap between the portions where each of the projection bosses  5442  and each of the third fastening projections  5467  are coupled may be open in the radial direction. Additionally, a portion of the fan  5450 , specifically, a portion of the shroud  5457 , may protrude outward in the radial direction of the second support part  5440  through the open portions. 
     The fan base  5460  described above may serve as a coupling medium for coupling between the fan module  540 ,  545  and the filter module  550 , and guide a suction flow at the entrance of the fan module  540 ,  545  to improve the suction and discharge performance of the fan module  540 ,  545 . 
     Aspect of Air Flow of Portable Air Purifier 
       FIG.  17    is a view showing an aspect of the air flow of the portable air purifier of one embodiment. 
     In  FIG.  17   , some components are omitted from the portable air purifier. 
     Hereinafter, an aspect of the air flow of the portable air purifier in the embodiment is described with reference to  FIGS.  4  and  17   . 
     Referring to  FIGS.  4  and  17   , as the fan module  540 ,  545  operates, air behind the portable air purifier  50  flows into the portable air purifier  50 . At this time, the air behind the portable air purifier  50  may pass through the suction surface through the first suction inlet  570   a  formed on the rear surface cover  580 . 
     The air having passed through the suction surface and being introduced into the portable air purifier  50  passes through the filter  559 , and while the air passes through the filter  559 , the filter  60  can filter physical particles such as dust/fine dust/ultra fine dust and the like, chemical substances such as odorant particles/harmful gases and the like, and microorganisms such as germs/viruses and the like, that are included in the air. 
     At this time, the air may be suctioned into the filter  559  through the suction surface that has as much surface area as the filter surface. Additionally, the air suctioned through the suction surface may be filtered through the filter surface that has as much surface area as the fan module  540 ,  545 . 
     That is, air may be suctioned and filtered effectively through the suction surface and the filter surface that have sufficient surface areas corresponding to the surface area of the fan module  540 ,  545 . Additionally, since the suction surface, the filter surface and the fan module  540 ,  545  are disposed in a straight line, air may be suctioned and filtered effectively while flow loss is minimized. 
     The air having passed through the filter  559 , i.e., purified air, may flow into the fan module  540 ,  545  through the fan inlet  5462 . The flow of the air passing through the fan inlet  5462  may be guided by the bell mouth  5463 , and accordingly, a smooth inflow of air to the fan module  540 ,  545  may be induced effectively. 
     The air being introduced into the fan module  540 ,  545  may be discharged in a mixed flow direction while being discharged from the front of the fan module  540 ,  545  through the fan outlet  5430   a . The mixed flow direction may be defined as a front-side diagonal direction. 
     The air, discharged from the front of the fan module  540 ,  545 , i.e., purified air, passes through the fan cover  530 , and is discharged from the front of the portable air purifier  50 . At this time, the purified air may pass through the discharge surface through the discharge outlet  510   a  formed on the front cover  510 . 
     The purified air may be discharged through the discharge surface that has as much surface area as the suction surface, the filter surface and the fan module  540 ,  545 . That is, the purified air may be discharged effectively through the discharge surface that has a sufficient surface area corresponding to the surface area of the suction surface, the surface area of the filter surface and the surface area of the fan module  540 ,  545 . Further, since the suction surface, the filter surface, the fan module  540 ,  545  and the discharge surface are disposed in a straight line, air may be suctioned and filtered, and purified air may be discharged, effectively, while flow loss is minimized. 
     Effect of Portable Air Purifier with Mixed Flow Fan-Type Fan 
     The portable air purifier  50  in the embodiment include a mixed flow fan type- fan  5450 . The portable air purifier  50  may produce the following effects. 
     First, since the fan module  540 ,  545  includes a mixed flow fan-type fan  5450 , the fan module  540 ,  545  may ensure improvement in air purification performance, compared to a fan module including an axial flow fan-type fan. 
     The axial flow fan allows air to be suctioned and discharged in a straight line. The axial flow fan may have a small thickness, and can be applied to a small-sized air purifier. 
     However, the performance of the axial flow fan significantly deteriorates at fixed pressure. For example, if the density or the thickness of the filter  559  increases to enhance filtering performance, the suction and discharge performance of the axial flow fan may significantly deteriorate. Accordingly, it is difficult to apply an axial flow fan to a portable air purifier with a high performance filter. 
     The mixed flow fan is somewhere between an axial flow fan and a centrifugal fan, and ensures more excellent performance at fixed pressure than the axial flow fan on condition that the mixed flow fan has the same size as the axial flow fan. However, the length of a mixed flow fan in the axial direction is greater than that of an axial flow fan on condition that the mixed flow fan has the same size as the axial flow fan. 
     However, the axial flow fan is inappropriate to send high-pressure high-speed air. Accordingly, a portable air purifier to which an axial flow fan is applied needs to further include a structure such as a guide vane. For example, a guide vane may be formed in the air discharge part  532 ,  533  of the fan cover  530 . The guide vane may be a cause for an increase in the length of the fan cover  530  in the first direction, i.e., the thickness of the fan cover  530 . 
     An increase in the thickness of the fan cover  530 , caused by the guide vane, results in a decrease in the length of the axial flow fan in the first direction due to the limited space in the portable air purifier, and a deterioration in the suction and discharge performance of the axial flow fan. 
     Unlike an axial flow fan, a mixed flow fan is appropriate to send high-pressure high-speed air. That is, without a structure such as a guide vane, the mixed flow fan may send air much farther than the axial flow fan. 
     For this reason, in the embodiment, the fan cover  530  excludes a structure such as a guide vane. Accordingly, the thickness of the fan cover  530  decreases, and the fan module  540 ,  545  is small enough to be inserted into the air discharge part  532 ,  533 . For example, the length of the fan module  540 ,  545  in the first direction may be determined to the extent that the front surface of the fan module  540 ,  545  and the front surface of the fan cover  530  constitute the same surface. That is, the length of the fan module  540 ,  545  in the first direction may extend by a length occupied by a guide vane. 
     As the size of the fan module  540 ,  545  increases, the suction and discharge performance of the fan module  540 ,  545  improves, enabling the portable air purifier  50  in the embodiment to ensure improvement in air purification performance. 
     Additionally, in the structure of the fan module  540 ,  545 , the fan case  5430 ,  5440  does not surround the fan  5450  from the outside in the radial direction. That is, the fan  5450  may be formed to protrude further in the centrifugal direction than the inner circumferential surface of the second support part  5440 . Accordingly, at least a portion of the fan  5450  may protrude to a gap between the second support part  5440  and the base plate  5461 . 
     Since the fan  5450  protrudes further in the centrifugal direction than the inner circumferential surface of the second support part  5440  as described above, the size of the fan  5450  may increase. 
     As the size of the fan module  540 ,  545  increases as described above, the suction and discharge performance of the fan module  545 ,  545  improves, enabling the portable air purifier  50  in the embodiment to ensure improvement in air purification performance. 
     Second, since the fan module  540 ,  545  includes a mixed flow fan-type fan  5450 , the range in which the portable air purifier  50  discharges air may expand. 
     A mixed flow fan can discharge air in the mixed flow direction, and accordingly, purified air discharged through the discharge surface may be discharged in the mixed flow direction, i.e., a direction between the front and the centrifugal direction. 
     When it comes to a small-sized portable air purifier  50 , if purified air is discharged toward the front only in a straight line, the range of the discharge of the purified air is limited to a range corresponding to the discharge surface. 
     If the purified air is discharged within a range corresponding to the discharge surface, even considering the properties of the small-sized portable air purifier  50 , limitations are imposed on the use of the portable air purifier  50 . 
     For example, the user has to keep holding up the portable air purifier  50  or has to accurately adjust the position of the portable air purifier  50  such that the discharge outlet  510   a  faces the user’s face, causing inconvenience to the user. 
     The portable air purifier  50  in the embodiment may discharge high-pressure high-speed air in a direction between the front and the centrifugal direction. Accordingly, purified air may spread to a large area as well as reaching a far corner, enabling the portable air purifier  50  to ensure improvement in air purification performance. 
     Third, each fan module  540 ,  545  includes the mixed flow fan-type fan  5450 , and a plurality of fan modules  540 ,  545  are stacked, allowing purified air to be discharged far away. 
     As described above, a mixed flow fan can discharge air in the mixed flow direction. At this time, a collision between air discharged from the first fan module  540  and air discharged from the second fan module  545  may occur, in the portion where the fan modules  540 ,  545  are adjacent to each other. 
     For example, air may be discharged obliquely downward at the lower side of the first fan module  540  adjacent to the second fan module  545 , and air may be discharged obliquely upward at the upper side of the second fan module  545  adjacent to the first fan module  540 . 
     At this time, a portion of the air discharged from the first fan module  540  and a portion of the air discharged from the second fan module  545  may collide with each other. Thus, their radiuswise speed vector decreases, and their frontwise speed vector may increase. 
     A decrease in the radiuswise speed vector and an increase in the frontwise speed vector denote the direction of speed vector of air discharged from the portable air purifier  50  changes to a direction close to the front. 
     As a result, the portable air purifier  50  discharges air mainly toward the front, and allows the air to reach a far corner, ensuring improvement in air purification performance. 
     Second Embodiment of Portable Air Purifier 
     Entire Structure of Fan 
       FIG.  18    is a front perspective view showing a front surface side of a fan provided in a portable air purifier of another embodiment,  FIG.  19    is a rear perspective view showing a rear surface side of the fan in  FIG.  18   , and  FIG.  20    is a front view showing the front surface side of the fan in  FIG.  18   . 
     Referring to  FIGS.  18  to  20   , the portable air purifier of another embodiment and the portable air purifier of the above-described embodiment have different structures for a fan  6450 . 
     The fan  6450  in the embodiment may include a plurality of fan blades  5455 . Each of the fan blades  5455  may include a leading edge  5455   a , a trailing edge  5455   b , a shroud chord  5455   c , and a hub chord  5455   d . 
     The leading edge  5455   a  may be disposed at a front end of the fan in a rotation direction and formed to be straight. The leading edge  5455   a  may be formed as a straight line that is disposed at the front end of the fan  5450  in the rotation direction of the fan  5450  and extends in a radial direction. 
     The trailing edge  5455   b  may be disposed at a rear end of the fan in the rotation direction and formed to be straight. The trailing edge  5455   b  may be formed as a straight line that extends in a direction between an axial direction and the radial direction. 
     The shroud chord  5455   c  may connect one end of the leading edge  5455   a  and one end of the trailing edge  5455   b . The shroud chord  5455   c  may extend from an inner circumferential surface of a shroud  5457 . 
     The hub chord  5455   d  may connect the other end of the leading edge  5455   a  and the other end of the trailing edge  5455   b . The hub chord  5455   d  may extend from an outer circumferential surface of a hub  5451 . 
     Additionally, one end of the leading edge  5455   a  and one end of the trailing edge  5455   b  may be connected to the inner circumferential surface of the shroud  5457 . Additionally, the other end of the leading edge  5455   a  and the other end of the trailing edge  5455   b  may be connected to an outer circumferential surface of a skirt part  5453 . 
     The fan blade  6455  may include a fan blade front surface  6455   e  and a fan blade rear surface  6455   f  which connect the leading edge  5455   a  and the trailing edge  5455   b . Both the fan blade front surface  6455   e  and the fan blade rear surface  6455   f  correspond to surfaces formed into shapes surrounded by the leading edge  5455   a , the trailing edge  5455   b , the shroud chord  5455   c , and hub chord  5455   d . Among them, the fan blade front surface  6455   e  is a surface disposed further forward than the fan blade rear surface  6455   f  in the rotation direction and is disposed at one side in the axial direction, and the fan blade rear surface  6455   f  corresponds to an opposite surface thereof. 
     Additionally, the fan  6450  may further include a front end projection part  6456 . The front end projection part  6456  may protrude forward from a front end of the fan blade  6455  in the rotation direction. 
     Structure of Front End Projection Part 
       FIG.  21    is an enlarged view showing portion “XXI” in  FIG.  20   , and  FIG.  22    is an enlarged view showing portion “XXII” in  FIG.  21   . 
     Referring to  FIGS.  19 ,  21 , and  22   , the front end projection part  6456  may be formed in a way that at least a part of the front end projection part  6456  protrudes further forward than a front end reference line L in the rotation direction. 
     The front end reference line L is defined as a straight line connecting a connection point of the front end of the fan blade  6455  in the rotation direction and the hub  5451  and a connection point of the front end of the fan blade  6455  in the rotation direction and the shroud. In other words, the front end reference line L may also be defined as a straight line that is substantially the same as a straight line formed by the leading edge  5455   a . 
     When the front end reference line L is substantially the same as the straight line formed by the leading edge  5455   a , the front end projection part  6456  may be formed to protrude from the leading edge  5455   a . 
     The front end projection part  6456  may protrude forward from the leading edge  5455   a  in the rotation direction. The front end projection part  6456  may protrude further forward than the shroud chord  5455   c , specifically, a connection point of the leading edge  5455   a  and the shroud chord  5455   c , in the rotation direction. 
     In the embodiment, the shroud chord  5455   c  may be obliquely formed with a predetermined slant angle in a way that the shroud chord  5455   c  is disposed at one side in the axial direction from the trailing edge  5455   b  side toward the leading edge  5455   a  side, i.e., toward the frond side in the rotation direction. 
     Additionally, the front end projection part  6456  may be formed in a way that the front end projection part  6456  forms a slant angle parallel with the slant angle of the shroud chord  5455   c  and protrudes forward from the leading edge  5455   a  in the rotation direction. That is, the front end projection part  6456  may constitute the same surface along with the shroud chord  5455   c  and the fan blade front surface  6455   e  and protrude forward from the leading edge  5455   a  in the rotation direction. 
     The front end projection part  6456  may be disposed in a way that a foremost side projection point  6456   a  of the front end projection part  6456  is disposed closer to the shroud  5457  than the hub  5451 . That is, a position of the front end projection part  6456  in the radial direction may be biased toward the shroud  5457  side. 
     It is preferable that a ratio of a distance d1 between the foremost side projection point  6456   a  of the front end projection part  6456  and the hub  5451  to a distance d2 between the foremost side projection point  6456   a  of the front end projection part  6456  and the shroud  5457  may be set to be in the range of 3:1 to 5:1. It is more preferable that the ratio of the distance d1 between the foremost side projection point  6456   a  of the front end projection part  6456  and the hub  5451  to the distance d2 between the foremost side projection point  6456   a  of the front end projection part  6456  and the shroud  5457  may be set to 4:1. 
     For example, when the distance d1 between the foremost side projection point  6456   a  of the front end projection part  6456  and the hub  5451  is 8 mm, a shape of the front end projection part  6456  may be determined such that the distance d2 between the foremost side projection point  6456   a  of the front end projection part  6456  and the shroud  5457  is 2 mm. 
     Additionally, the front end projection part  6456  may be obliquely formed in a way that the front end projection part  6456  protrudes further toward one side in the axial direction as the front end projection part  6456  becomes to be close to the foremost side projection point  6456   a  of the front end projection part  6456  from the other end side of the leading edge  5455   a , i.e., in a centrifugal direction from the other end side of the leading edge  5455   a  adjacent to the hub  5451  toward the foremost side projection point  6456   a  of the front end projection part  6456 . 
     Accordingly, a shape of the fan blade  6455  in a section from the other end of the leading edge  5455   a  and the foremost side projection point  6456   a  of the front end projection part  6456  may be formed in a way that a length of the fan blade  6455  in the rotation direction gradually increases in the centrifugal direction. 
     Additionally, in the section between the foremost side projection point  6456   a  of the front end projection part  6456  and one end of the leading edge  5455   a , a projection length of the front end projection part  6456  may gradually decrease in the centrifugal direction. In other words, in the section between the foremost side projection point  6456   a  of the front end projection part  6456  and one end of the leading edge  5455   a , the projection length of the front end projection part  6456  may gradually increase from one end of the leading edge  5455   a  toward the foremost side projection point  6456   a  of the front end projection part  6456  in a centripetal direction. 
     That is, the projection length of the front end projection part  6456  may gradually increase from the other end of the leading edge  5455   a  toward the foremost side projection point  6456   a  of the front end projection part  6456  in the centrifugal direction, the foremost side projection point  6456   a  of the front end projection part  6456  may be a most protruding portion of the front end projection part  6456 , and the projection length of the front end projection part  6456  may gradually decrease from the foremost side projection point  6456   a  of the front end projection part  6456  toward one end of the leading edge  5455   a  in the centrifugal direction. 
     Accordingly, the shape of the entire fan blade  6455  is formed so that a width of the fan blade  6455  in the rotation direction gradually increases to a predetermined point (the foremost side projection point of the front end projection part) adjacent to the shroud  5457 . That is, the fan blade  6455  is provided in a way that an area of a portion of the fan blade  6455  adjacent to the shroud  5457  increases relative to a portion adjacent to the hub  5451  in the fan blade  6455 . 
     A flow of air passing through the fan  6450  while the air is suctioned and discharged by operation of the fan  6450  will be described. A speed of air passing through a portion adjacent to the shroud  5457  is greater than a speed of air passing through a portion adjacent to the hub  5451 . That is, a speed of air passing through an outer portion of the fan blade  6455  in the radial direction is greater than a speed of air passing through a central portion of the fan  6450  in the radial direction. This may be understood as a feature of a mixed flow fan which suctions air in an axial direction and discharges the air in a direction between the axial direction and a centrifugal direction. 
     In consideration of this feature, it may be understood that a larger amount of air may be blown from a region adjacent to the shroud  5457  than a region adjacent to the hub  5451  by the fan blade front surface  6455   e  which is a surface corresponding to a pressure surface. 
     In consideration of the above fact in the embodiment, the shape of the fan blade  6455  is determined in a way that an area of the region adjacent to the shroud  5457  is greater than an area of the region adjacent to the hub  5451  in the fan blade front surface  6455   e . To this end, the front end projection part  6456  is formed on the front end of the fan blade  6455  in the rotation direction. 
     As the fan blade  6455  is formed in the above-described shape, the fan blade  6455  may secure a larger contact area with air in a region which blows a larger amount of air than another region. 
     As a result, when a flow rate is the same, a flow rate blown by the fan blade  6455  per unit area of the fan blade  6455  may decrease. That is, as an area of a region which may blow a larger amount of air than another region increases, a pressure received by the fan blade  6455  per unit area while blowing air may decrease. 
     Additionally, due to a projection structure formed by the front end projection part  6456  in a way that a part of the fan blade  6455  protrudes, an increase in rigidity of the fan blade  6455  can be expected. 
     Additionally, in the embodiment, the other end of the leading edge  5455   a  and the foremost side projection point  6456   a  of the front end projection part  6456  are connected roundly in the front end projection part  6456 , for example. At this time, the front end projection part  6456  may be formed in a curved shape that is convex toward the trailing edge  5455   b , i.e., to the rear side in the rotation direction. 
     As the front end projection part  6456  is formed in the curved shape described above, structural stability of a front end portion of the fan blade  6455  in the rotation direction can be improved, and thus a more increase in rigidity of the fan blade  6455  can be expected. 
     That is, due to the structure of the fan  6450  in the embodiment as an example, a pressure received by the fan blade  6455  per unit area decreases, and rigidity of the fan blade  6455  itself increases. 
     Shape of Cross Section of Fan Blade 
       FIG.  23    is a cross-sectional view along line “XXIII-XXIII” in  FIG.  20   . 
     Referring to  FIGS.  18  and  23   , the fan blade  6455  may include the fan blade front surface  6455   e  disposed at one side in the axial direction and the fan blade rear surface  6455   f  disposed at the other side in the axial direction based on the leading edge  5455   a  and the trailing edge  5455   b . 
     The fan blade front surface  6455   e  corresponds to a pressure surface disposed at a side through which air being introduced into the fan  6450  is blown to a discharge outlet side. Additionally, the fan blade rear surface  6455   f  corresponds to a negative pressure surface disposed at a side at which air flown into the fan  6450  is suctioned. 
     In the embodiment, the fan blade front surface  6455   e  and the fan blade rear surface  6455   f  may be formed in shapes different from each other. 
     Specifically, the fan blade rear surface  6455   f  may be formed in the shape connecting the leading edge  5455   a  and the trailing edge  5455   b  straightly. That is, the fan blade rear surface  6455   f  may be formed in a flat shape. 
     Additionally, the fan blade front surface  6455   e  may roundly connect the leading edge  5455   a  and the trailing edge  5455   b . Specifically, the fan blade front surface  6455   e  may be formed in the shape connecting the leading edge  5455   a  and the trailing edge  5455   b  using a curved surface that is convex toward one side in the axial direction. A camber may be formed on the fan blade front surface  6455   e  formed as described above at one side of the fan blade  6455  in the axial direction. 
     As the shape of the fan blade  6455  is designed in a way that the camber is formed on the fan blade front surface  6455   e  as described above, the performance of the fan  6450  at fixed pressure can be further improved. Accordingly, the discharge performance of the fan  6450  can be further improved, and noise can also be effectively reduced compared to a fan blowing the same flow rate. 
     Additionally, as the camber is formed on only the fan blade front surface  6455   e , and the fan blade rear surface  6455   f  is formed in the flat shape, there is an advantage in molding the fan  6450  using a mold. Detailed description in relation to this is provided below. 
     Relationship Between Shape of Fan Blade and Mold 
       FIG.  24    is a front view showing a slide direction of a mold used for molding the fan of another embodiment, and  FIG.  25    is a side cross-sectional view showing the slide direction of the mold in  FIG.  24   . 
     In  FIG.  25   , a side cross-section of the fan is illustrated in a way that one side in the axial direction is an upper portion, and the other side in the axial direction is a lower portion. 
     Referring to  FIGS.  18 ,  19 ,  24 , and  25   , the fan  6450  in the embodiment may be manufactured in a molding manner using a mold. For example, the fan  6450  may be manufactured in an injection molding manner in which a molded product is formed by injecting a plastic material melted by heating into a mold and solidifying or curing the plastic material. 
     Generally, a molded product like the fan  6450  may be manufactured using a mold divided into two main parts. One of them is a first mold M 1  moved in the axial direction of the fan  6450  and engaged with or separated from the other mold. Additionally, the other one is a second mold M 2  obliquely moved in a direction between the axial direction, a circumferential direction, and the radial direction of the fan  6450  and engaged with or separated from the first mold. 
     Although the first mold M 1  may be divided into a plurality of molds, the first mold M 1  may also be provided as one mold. The second mold M 2  needs to be provided as in a way that second molds M 2  are divided by as much as at least the number of the fan blades  6455  due to the feature of the fan  6450  in which the plurality of fan blades  6455  are disposed in the circumferential direction of the fan  6450 . 
     Largest differences between the fan  6450  in the embodiment and another fan are the front end projection part  6456  provided on the front end of the fan blade  6455  in the rotation direction and the camber formed on the fan blade  6455 . 
     That is, the fan  6450  in the embodiment is has a complicated shape compared to fans formed in a way that a front end of a fan blade in a rotation direction is formed in a straight line shape and front surfaces and rear surfaces of fan blades have the flat shapes. 
     When the shape of the fan blade is complicated as described above, there is a high possibility that it is difficult to mold the fan using the mold. For example, there may be a problem that an additional postprocess is required after molding using the mold is completed, or the number of molds increases even when the molding of the fan is completed by only molding using the mold. 
     Considering the fact, in the embodiment, a design of the shape of the fan blade  6455  is proposed such that shapes like the front end projection part  6456  and the camber are applied to the fan blade  6455  without adding a postprocess or increasing the number of molds. 
     Accordingly, the front end projection part  6456  protrudes further than the front end reference line L and the shroud chord  5455   c  toward one side in the axial direction and the front in the rotation direction and does not protrude further than the shroud  5457  toward one side in the axial direction. 
     In the embodiment, portions such as a front surface of the shroud  5457 , a shroud projection  5458 , and the fan blade front surface  6455   e  are molded using the first mold M 1 , and portions such as the fan blade rear surface  6455   f , a rear surface of the shroud  5457 , and one region of the fan blade front surface  6455   e  which overlaps the shroud  5457  in the axial direction are molded using the second molds M 2 . 
     When the front end projection part  6456  protrudes further than the shroud  5457  toward one side in the axial direction, it is difficult to mold the fan  6450  using the first mold M 1  formed as one mold since it is difficult to mold the shroud projection  5458  extending along a straight line in the axial direction and the front end projection part  6456  protruding at a slat using one mold at the same time. 
     In consideration of the above fact in the embodiment, the front end projection part  6456  does not protrude further than the shroud  5457  toward one side in the axial direction. To this end, a position of the foremost side projection point  6456   a  of the front end projection part  6456  in the axial direction may be the same as a position of the shroud  5457  or may be disposed behind the shroud  5457 . Additionally, in the front end projection part  6456 , a section between the foremost side projection point  6456   a  of the front end projection part  6456  and the shroud  5457  may be formed in a flat shape perpendicular to a straight line in the axial direction. 
     As the shape of the front end projection part  6456  is determined as the above shape, in one side region of the fan  6450  in the axial direction molded using the first mold M 1 , i.e., a region between the front surface of the shroud  5457  and the shroud projection  5458 , only a structure, such as, the shroud projection  5458  protruding straightly in the axial direction, is present, and a structure protruding in other directions other than the axial direction is not present. Accordingly, the fan  6450  can be effectively molded even using the first mold M 1  formed as the one mold. 
     Additionally, in the embodiment, the fan blade front surface  6455   e  and the fan blade rear surface  6455   f  are formed in the shapes different from each other. That is, the camber is formed on only the fan blade front surface  6455   e , and the fan blade rear surface  6455   f  is formed in the flat shape. 
     In the embodiment, the second molds M 2  are divided by as much as the number of the fan blades  6455 , and the second molds M 2  are separated independently after the fan  6450  is completely molded. 
     When the second molds M 2  are separated from the fan  6450 , each of the second molds M 2  is obliquely moved in a direction between the axial direction, the circumferential direction, and the radial direction of the fan  6450 . When movement of the second mold M 2  in the circumferential direction is ignored, the second mold M 2  obliquely moves in a direction between the axial direction and the radial direction of the fan  6450 , and a movement direction of the second molds M 2  is parallel with a slant angle of the flat surface formed by the fan blade rear surface  6455   f . 
     When the camber is formed on not only the fan blade front surface  6455   e  but also the fan blade rear surface  6455   f , i.e., the fan blade rear surface  6455   f  is formed in a curved shape that is convex toward the other side in the axial direction, a projection structure which hinders movement of the second mold M 2  is present on the fan blade rear surface  6455   f . 
     At this time, the number of the second molds M 2  greater than the number of the fan blades  6455  is required, or an additional postprocess is required after molding is completed using the molds when it is difficult to complete the molding through the number of the second molds M 2  greater than the number of the fan blades  6455 . That is, after the fan blade rear surface  6455   f  is molded in a flat shape, an additional process of forming a corresponding portion into a curved surface is further required. 
     In consideration of the above fact in the embodiment, the camber is formed on only the fan blade front surface  6455   e , and the fan blade rear surface  6455   f  is formed in the flat shape. As a result, as the camber is formed on the fan blade  6455 , the performance of the fan  6450  at fixed pressure can be improved, and molding using the mold can also be performed without adding a postprocess or increasing the number of molds. 
     Operation and Effect of Fan 
       FIG.  26    is a graph showing a measurement result of a flow rate with respect to a fan speed of the portable air purifier of another embodiment, and  FIG.  27    is a graph showing a measurement result of a noise with respect to the flow rate of the portable air purifier of another embodiment. 
     Components other than a fan in a comparative target air purifier illustrated in  FIGS.  26  and  27    are the same as those of the air purifier in the embodiment. Additionally, differences between the fan of the comparative target air purifier and the fan of the portable air purifier in the embodiment are a front end projection part not formed on a fan blade of the fan of the comparative target air purifier illustrated in  FIGS.  26  and  27    and both a front surface and a rear surface of the fan blade of the fan of the comparative target air purifier formed into flat shapes. 
     Hereinafter, operation and effects of the portable air purifier in the embodiment will be described with reference to  FIGS.  21  to  27   . 
     Referring to  FIGS.  21  and  22   , the shape of the fan blade  6455  is determined in a way that the area of the region adjacent to the shroud  5457  is greater than the area of the region adjacent to the hub  5451  in the fan blade front surface  6455   e . To this end, the front end projection part  6456  is formed on the front end of the fan blade  6455  in the rotation direction. 
     As the fan blade  6455  is formed in the shape described above, an area of the entire fan blade  6455  increases, and particularly, an area of a region capable of blowing a larger amount of air than another region can also increase. 
     Accordingly, the discharge performance of the fan  6450  can be improved, and a pressure received by the fan  6450  per unit area can also be reduced while the fan  6450  operates. 
     Additionally, due to a projection structure formed by the front end projection part  6456  in a way that a part of the fan blade  6455  protrudes, an increase in rigidity of the fan blade  6455  can be expected. 
     Additionally, in the embodiment, the shape of the fan blade  6455  is designed in a way that the camber is formed on the fan blade front surface  6455   e  as illustrated in  FIG.  23   . Accordingly, the rigidity of the fan blade  6455  can be improved, and the performance of the fan  6450  at fixed pressure can also be improved further. 
     As a result, a portable air purifier A in the embodiment provides improved discharge performance and reduced noise compared to a comparative target air purifier B. That is, the portable air purifier A in the embodiment can provide a higher flow rate than the comparative target air purifier B under a condition that the fan  6450  rotates at the same speed (see  FIG.  26   ) and can provide an effect of generating smaller noise than the comparative target air purifier B at the same flow rate (see  FIG.  27   ). 
     Meanwhile, referring to  FIGS.  21  to  23   , the front end projection part  6456  protrudes further than the front end reference line L and the shroud chord  5455   c  toward one side in the axial direction and the front in the rotation direction and does not protrude further than the shroud  5457 , particularly, the shroud projection  5458  toward one side in the axial direction. 
     The shroud projection  5458  corresponds to a component disposed at the foremost side in the fan  6450  in the axial direction. Accordingly, when the front end projection part  6456  protrudes further than the shroud projection  5458  toward one side in the axial direction, a length of the entire fan  6450  in the axial direction increases as much as the length by which the front end projection part  6456  protrudes further than the shroud projection  5458  toward one side in the axial direction. 
     When the length of the fan  6450  in the axial direction increases, a size of the entire fan module increases, and thus a size of the entire portable air purifier increases. This is not a preferable change to the portable air purifier in which portability is important. 
     There may be a method of changing a design of the fan in a way that a size of the entire fan module does not increase. However, in this case, the design should be changed in a way that the length of the fan blade  6455  in the axial direction decreases as much as the length by which the front end projection part  6456  protrudes further than the shroud projection  5458  toward one side in the axial direction. However, when the length of the fan blade  6455  in the axial direction decreases, a contact area of the fan blade  6455  with air decreases as much, and thus there is a problem that the discharge performance of the fan module is degraded. 
     In consideration of the above fact in the embodiment, as the front end projection part  6456  does not protrude further than the shroud projection  5458  toward one side in the axial direction, an increase in the length of the entire fan  6450  in the axial direction due to the front end projection part  6456  is not allowed. As a result, the portable air purifier in the embodiment can provide an effect of further improved discharge performance without increasing the size of the portable air purifier. 
     The present invention has been described with reference to embodiments illustrated in the accompanying drawings, but this is merely exemplary. It will be understood by those skilled in the art that various modifications and equivalent other example embodiments may be made from the embodiments of the present invention. Therefore, the scope of the present invention is defined by the appended claims. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           50 : Portable air purifier 
           510 : Front panel 
           520 : Case 
           530 : Fan cover 
           531 : Upper cover part 
           532 : Upper air discharge part 
           533 : Lower air discharge part 
           534 : First fastening projection 
           535 : Lower cover part 
           537 : Side surface 
           540 : First fan module 
           545 : Second fan module 
           550 : Filter module 
           551 : Filter case 
           552 : Penetration hole 
           553 : Second fastening projection 
           559 : Filter 
           560 : Battery 
           570 : Rear surface panel 
           580 : Rear surface cover 
           5410 : Shaft 
           5420 : Motor 
           5421 : Stator 
           5423 : Rotor 
           5430 : First support part 
           5430   a : Fan outlet 
           5431 : Support plate 
           5433 : Boss 
           5435 : Bearing 
           5440 : Second support part 
           5441 : Fastening hole 
           5442 : Projection boss 
           5443 : Side rib 
           5445 : Third support part 
           5450 ,6450: Fan 
           5451 : Hub 
           5452 : Hub plate part 
           5452   a : Shaft coupling part 
           5453 : Skirt part 
           5454 : Inner projection part 
           5455 ,6455: Fan blade 
           5455   a : Leading edge 
           5455   b : Trailing edge 
           5455   c : Shroud chord 
           5455   d : Hub chord 
           5457 : Shroud 
           5458 : Shroud projection 
           5460 : Fan base 
           5461 : Base plate 
           5462 : Fan inlet 
           5463 : Bell mouth 
           5465 : Fastening boss 
           5467 : Third fastening projection 
           6455   e : Fan blade front surface 
           6455   f : Fan blade rear surface 
           6456 : Front end projection part 
           6456   a : Foremost side projection point