Abstract:
A drying apparatus has a casing, a cavity formed in the casing for receiving an object, a fan located in the casing and creating an airflow, a motor provided in the casing for driving the fan and ducting for carrying the airflow from the fan to at least one opening arranged to emit the airflow into the cavity, wherein the ducting includes at least one air duct in which at least one vane is located, the vane extending in the direction of airflow and dividing the air duct into a plurality of airflow portions.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 USC 371 of International Application No. PCT/GB2006/002084, filed Jun. 7, 2006, which claims the priority of United Kingdom Application No. 0515754.0, filed Jul. 30, 2005, the contents of which prior applications are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to drying apparatus which makes use of a narrow jet of high velocity, high pressure air to dry an object, including part of the human body. Particularly, but not exclusively, the invention relates to a hand dryer in which the air jet is emitted through a slot-like opening in the casing of the hand dryer. 
     BACKGROUND OF THE INVENTION 
     The use of air jets to dry hands is well known. Examples of hand dryers which emit at least one air jet through a slot-like opening are shown in GB 2249026A, JP 2002-034835A and JP 2002306370A. However, in practice it is very difficult to achieve an evenly distributed airflow of sufficiently high momentum to dry the user&#39;s hands efficiently in an acceptably short length of time. Furthermore, the amount of noise emitted by a motor suitable for generating an airflow of sufficiently high momentum adequately to dry the user&#39;s hands can be unacceptably high. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide drying apparatus in which an airflow of sufficient momentum efficiently to dry the user&#39;s hands is produced and in which the noise emitted by the motor is improved in comparison to prior art devices. It is a further object of the present invention to provide drying apparatus in which the noise emitted by the apparatus is comparatively low. 
     A first aspect of the invention provides drying apparatus having a casing, a cavity formed in the casing for receiving an object, a fan located in the casing and capable of creating an airflow, a motor provided in the casing for driving the fan and ducting for carrying the airflow from the fan to at least one opening arranged to emit the airflow into the cavity, wherein the ducting comprises at least one air duct in which at least one vane is located, the or each vane extending in the direction of airflow and dividing the air duct into a plurality of airflow portions. 
     Preferably, the or each vane is positioned in the air duct such that the distance between the said vane and any adjacent wall of the air duct or further vane is no more than a predetermined value. This predetermined value is determined in such a way that it is no greater than the half-wavelength of the noise emitted by the motor. In this way, standing waves are prevented form building up in the air duct but plane waves are allowed to pass along the air duct. This reduces the noise emitted by the machine overall and so enhances the comfort with which the user is able to use the drying apparatus. 
     The predetermined value is therefore calculated as a function of both the operating speed of the motor and the speed of sound in the airflow passing along the air duct. Motor speeds vary from product to product and the speed of sound in the airflow will depend upon the expected operating temperature of the apparatus. However, an optimum predetermined value can be calculated. The formula to be used is thus: 
     
       
         
           
             
               Predetermined 
               ⁢ 
               
                   
               
               ⁢ 
               Value 
             
             = 
             
               
                 30 
                 × 
                 Speed 
                 ⁢ 
                 
                     
                 
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                 of 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 sound 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 in 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 air 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 duct 
               
               
                 Operating 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 speed 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 of 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 the 
                 ⁢ 
                 
                     
                 
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                 motor 
               
             
           
         
       
     
     If the normal operating temperature of the apparatus is approximately 55° C., this can be simplified to: 
     
       
         
           
             
               Predetermined 
               ⁢ 
               
                   
               
               ⁢ 
               Value 
             
             = 
             
               10800 
               
                 Operating 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 speed 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 of 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 the 
                 ⁢ 
                 
                     
                 
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                 motor 
               
             
           
         
       
     
     In a preferred embodiment, the operating speed of the motor is substantially 90,000 rpm which puts the predetermined value at 120 mm, although the preferred range of predetermined values is between 100 mm and 150 mm. In the embodiment, the distance between any point on the or each vane and the wall of the air duct or adjacent vane (measured in a direction perpendicular to the airflow) is sufficiently small to prevent standing waves being able to build up. The noise of the hand dryer is thus improved in comparison to the noise which would have been emitted absent the vanes. 
     It is preferred that more than one vane is arranged in the or each air duct and that the vanes are arranged in rows, more preferably rows which overlap one another. If the breadth of each air duct increases in the direction of the airflow, each successive row of vanes has a higher number of vanes than the previous row. 
     The provision of the vanes in the air ducts assists in strengthening the structure of the air ducts and their direction helps to maintain the direction of airflow within the ducts, particularly as the duct becomes broader. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention in the form of a hand dryer will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of drying apparatus according to the invention in the form of a hand dryer; 
         FIG. 2  is a perspective view of the hand dryer of  FIG. 1 ; 
         FIG. 3  is a side sectional view of the hand dryer of  FIG. 1 ; 
         FIG. 4  is a side sectional view, shown on an enlarged scale, of the upper ends of the air ducts forming part of the hand dryer of  FIG. 1 ; 
         FIG. 5  is a schematic sectional side view, shown on a further enlarged scale, of the slot-like opening located in the front wall of the cavity of the hand dryer of  FIG. 1 ; 
         FIG. 6  is a schematic sectional side view, shown on the same further enlarged scale, of the slot-like opening located in the rear wall of the cavity of the hand dryer of  FIG. 1 ; 
         FIG. 7  is an isometric view of the ducting forming part of the hand dryer of  FIG. 1  shown in isolation from the other components of the apparatus; and 
         FIG. 8  is a sectional view of one of the air ducts of  FIG. 7  showing the location of a plurality of vanes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to  FIGS. 1 and 2 , the hand dryer  10  shown in the drawings comprises an outer casing  12  having a front wall  14 , a rear wall  16 , an upper face  18  and side walls  20 ,  22 . The rear wall  16  can incorporate fixing devices (not shown) for securing the hand dryer  10  to a wall or other structure prior to use. An electrical connection (not shown) is also provided on the rear wall or elsewhere on the casing  12 . A cavity  30  is formed in the upper part of the casing  12  as can be seen from  FIGS. 1 and 2 . The cavity  30  is open at its upper end and delimited thereat by the top of the front wall  14  and the front of the upper face  18 . The space between the top of the front wall  14  and the front of the upper face  18  forms a cavity entrance  32  which is sufficiently wide to allow a user&#39;s hands to be introduced to the cavity  30  through the cavity entrance  32 . The cavity  30  is also open to the sides of the hand dryer  10  by appropriate shaping of the side walls  20 ,  22 . 
     The cavity  30  has a front wall  34  and a rear wall  36  which delimit the cavity  30  to the front and rear respectively. Located in the lowermost end of the cavity  30  is a drain  38  which communicates with a reservoir (not shown) located in the lower part of the casing  12 . The purpose of the drain and reservoir will be described below. 
     As shown in  FIG. 3 , a motor (not shown) is located inside the casing  12  and a fan  40 , which is driven by the motor, is also located inside the casing  12 . The motor is connected to the electrical connection and is controlled by a controller  41 . The inlet  42  of the fan  40  communicates with an air inlet  44  formed in the casing  12 . A filter  46  is located in the air passageway connecting the air inlet  44  to the fan inlet  42  so as to prevent the ingress of any debris which might cause damage to the motor or the fan  40 . The outlet of the fan  40  communicates with a pair of air ducts  50 ,  52  which are located inside the casing  12 . The front air duct  50  is located primarily between the front wall  14  of the casing  12  and the front wall  34  of the cavity  30 , and the rear air duct  52  is located primarily between the rear wall  16  of the casing  12  and the rear wall  36  of the cavity  30 . 
     The air ducts  50 ,  52  are arranged to conduct air from the fan  40  to a pair of opposed slot-like openings  60 ,  62  which are located in the front and rear walls  34 ,  36  respectively of the cavity  30 . The slot-like openings  60 ,  62  are arranged at the upper end of the cavity  30  in the vicinity of the cavity entrance  32 . The slot-like openings  60 ,  62  are each configured so as to direct an airflow generally across the cavity entrance  32  towards the opposite wall of the cavity  30 . The slot-like openings  60 ,  62  are offset in the vertical direction and angled towards the lowermost end of the cavity  30 . 
       FIG. 4  shows the upper ends of the air ducts  50 ,  52  and the slot-like openings  60 ,  62  in greater detail. As can be seen, the walls  54   a ,  54   b  of the air duct  50  converge to form the slot-like opening  60  and the walls  56   a ,  56   b  of the air duct  52  converge to form the slot-like opening  62 . Even greater detail can be seen in  FIGS. 5 and 6 .  FIG. 5  shows that the slot-like opening  60  has a width of W 1  and  FIG. 6  shows that the slot-like opening  62  has a width of W 2 . The width W 1  of the slot-like opening  60  is smaller than the width W 2  of the slot-like opening  62 . The width W 1  is 0.3 mm and the width W 2  is 0.4 mm. 
     Each pair of walls  54   a ,  54   b ,  56   a ,  56   b  is arranged so that the respective walls approach one another as they approach the respective slot-like opening  60 ,  62 . If an imaginary axis  70  is considered to lie midway between each pair of walls, as is shown in  FIGS. 5  and  6 , then each wall  54   a ,  54   b ,  56   a ,  56   b  lies at an angle of substantially 7° to the respective axis  70 . Thus the angle formed between each pair of walls  54   a ,  54   b ,  56   a ,  56   b  is thus substantially 14°. This angle has been found to be advantageous, although it could be varied by several degrees. Angles of between 100 and 200 may be used. 
     Sensors  64  are positioned in the front and rear walls  34 ,  36  of the cavity  30  immediately below the slot-like openings  60 ,  62 . These sensors  64  detect the presence of a user&#39;s hands which are inserted into the cavity  30  via the cavity entrance  32  and are arranged to send a signal to the motor when a user&#39;s hands are introduced to the cavity  30 . As can be seen from  FIGS. 1 and 3 , the walls  54   a ,  54   b ,  56   a ,  56   b  of the ducts  50 ,  52  project slightly beyond the surface of the front and rear walls  34 ,  36  of the cavity  30 . The inward projection of the walls  54   a ,  54   b ,  56   a ,  56   b  of the ducts  50 ,  52  reduces the tendency of the user&#39;s hands to be sucked towards one or other of the walls  34 ,  36  of the cavity, which enhances the ease with which the hand dryer  10  can be used. The positioning of the sensors  64  immediately below the inwardly projecting walls  54   a ,  54   b ,  56   a ,  56   b  of the ducts  50 ,  52  also reduces the risk of the sensors  64  becoming dirty and inoperative. 
     As can be seen from  FIG. 2 , the shape of the cavity entrance  32  is such that the front edge  32   a  is generally straight and extends laterally across the width of the hand dryer  10 . However, the rear edge  32   b  has a shape which consists of two curved portions  33  which generally follow the shape of the backs of a pair of human hands as they are inserted downwardly into the cavity  30  through the cavity entrance  32 . The rear edge  32   b  of the cavity entrance  32  is substantially symmetrical about the centre line of the hand dryer  10 . The intention of the shaping and dimensioning of the front and rear edges  32   a ,  32   b  of the cavity entrance  32  is that, when a user&#39;s hands are inserted into the cavity  30  through the cavity entrance  32 , the distance from any point on the user&#39;s hands to the nearest slot-like opening is substantially uniform. 
     The air ducts  50 ,  52  form part of the ducting  90  which lies between the fan  40  and the slot-like openings  60 ,  62 . A perspective view of the ducting  90  is shown in  FIG. 7 . The ducting  90  includes a scroll  92  which lies adjacent the fan  40  and receives the airflow generated by the fan  40 . The scroll  92  communicates with a first chamber  94  which is generally square in cross-section, although the cross-section could easily be generally circular. The intention is that the cross-section of the chamber  94  should have dimensions which are substantially the same in both directions. Immediately downstream of the chamber  94  is a Y-junction  96  downstream of which the air ducts  50 ,  52  are located. As has been described above, the air ducts  50 ,  52  pass towards the upper end of the casing  12  with the front air duct  50  being located between the front wall  14  of the casing  12  and the front wall  34  of the cavity  30  and the rear duct  52  being located between the rear wall  16  of the casing  12  and the rear wall  36  of the cavity  30 . The air ducts  50 ,  52  communicate with the slot-like openings  60 ,  62  at the upper end of the cavity  30 . 
     The ducting  90  is designed so that the cross-sectional area of the ducting  90  gradually transforms from the generally square (or circular) shape of the chamber  94  to the slot-like shape of the openings in a smooth and gradual manner. Immediately downstream of the chamber  94 , the ducting divides into the air ducts  50 ,  52 , at the upstream end of which the cross-sectional area is still generally square in shape—ie, the breadth and depth of the cross-section are substantially similar. However, the cross-section changes gradually with distance from the chamber  94  so that the breadth of each duct  50 ,  52  increases as the depth reduces. All of the changes are smooth and gradual to minimise any frictional losses. 
     At a point  98  immediately upstream of each of the slot-like openings  60 ,  62 , the cross-sectional area of each of the air ducts  60 ,  62  begins to decrease so as to cause the velocity of the airflow travelling towards the slot-like openings  60 ,  62  to increase dramatically. However, between the chamber  94  and the point  98  in each air duct  50 ,  52 , the total cross-sectional area of the ducting (ie. the combined cross-sectional area of the air ducts  50  and  52 ) remains substantially constant. 
       FIG. 8  shows the air duct  50  in section, the section being taken along the centre-line of the duct  50  itself. As can be seen, the lower end  50   a  of the duct  50  has a generally elongate cross-section and is adapted to communicate with one of the branches of the Y-junction  96 . The upper end  50   b  of the air duct  50  communicates with the point  98  which is immediately upstream of the slot-like opening  60 . The air duct  50  broadens as it approaches the upper end  50   b.    
     Inside the air duct  50 , three vanes  100  are provided. The vanes  100  have an elongate shape and lie so as to extend in the direction of the airflow passing along the air duct  50 . To this end, the single upstream vane  100   a  is positioned so as to lie along the central axis of the duct  50  but the downstream vanes  100   b  are inclined slightly towards the side walls of the duct  50  so as to follow the steamlines of the airflow passing along the duct  50 . Each vane  100  has an upstream edge  102  and a downstream edge  104 , and each edge  102 ,  104  is radiussed so as to minimise any turbulence created in the airflow by virtue of their presence. 
     The position of the vanes  100   a ,  100   b  within the duct  50  is determined so that the distance between any one vane  100   a ,  100   b  and either the wall of the air duct  50  or an adjacent vane  100   b  is no more than half of the wavelength of the noise emitted by the motor. This is determined according to the operating speed of the motor and the velocity of sound within the airflow travelling along the air duct  50 . It will be appreciated that this distance can be calculated according to the formula: 
     
       
         
           
             
               Predetermined 
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               Value 
             
             = 
             
               
                 30 
                 × 
                 Speed 
                 ⁢ 
                 
                     
                 
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                 of 
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                 sound 
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                 in 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 air 
                 ⁢ 
                 
                     
                 
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                 duct 
               
               
                 Operating 
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                 speed 
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                 of 
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                 motor 
               
             
           
         
       
     
     It will also be appreciated that the speed of sound in the airflow will vary according to the temperature and pressure of the airflow. To simplify the calculation, it has been found effective to use in this equation the speed of sound in the airflow at the slot-like openings, which is the point at which the temperature is likely to be lowest. Under normal operating conditions of the hand dryer shown in the embodiment, we expect the airflow temperature at the slot-like openings to be approximately 55° C.—at which temperature the speed of sound in air is approximately 360 m/s. The predetermined value can them be calculated using the simplified formula: 
     
       
         
           
             
               Predetermined 
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               Value 
             
             = 
             
               10800 
               
                 Operating 
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                 speed 
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                 of 
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                 motor 
               
             
           
         
       
     
     In the embodiment, the motor is designed to operate at a speed of approximately 90,000 rpm. The predetermined value is then calculated to be 120 mm. Other speeds of the motor result in the predetermined value being selected to be between 100 mm and 150 mm. 
     Having calculated the predetermined value, the vanes  100   a ,  100   b  are positioned in the air duct  50  so that all relevant distances are no more than this value—and can be considerably less. The distances V 1 -V 4  which are to be no greater than the predetermined value are shown in  FIG. 8 . 
     As the breadth of the air duct  50  increases, the need to provide larger numbers of vanes also increases. The vanes  100  are thus arranged in rows with a single vane  100   a  provided in the first, upstream row and two vanes  100   b  provided in the next row. If the breadth of the air duct  50  had been sufficiently large in the downstream area, or if the predetermined value had been smaller so that only two vanes  100   b  were insufficient, three vanes  100   b  could easily have been provided. 
     The rows of vanes  100  are located so that the upstream edges  102  of the vanes  100   b  overlap with the downstream edge  104  of the vane  100   a . This ensures that no point of the air duct  50  is left unrestricted in terms of the distance between the vanes  100  and the walls of the duct  50 . 
     It will be appreciated that vanes  100  are provided in the air duct  52  in the same manner as those provided in the air duct  50 , with the predetermined value being calculated in the same way. 
     The hand dryer  10  described above operates in the following manner. When a user&#39;s hands are first inserted into the cavity  30  through the cavity entrance  32 , the sensors  64  detect the presence of the user&#39;s hands and send a signal to the motor to drive the fan  40 . The fan  40  is thus activated and air is drawn into the hand dryer  10  via the air inlet  44  at a rate of approximately 20 to 40 litres per second and preferably at a rate of least 25 to 27 litres per second, more preferably air is drawn into the hand dryer  10  at a rate of 31 to 35 litres per second. The air passes through the filter  46  and along the fan inlet  42  to the fan  40 . The airflow leaving the fan  40  is divided into two separate airflows; one passing along the front air duct  50  to the slot-like opening  60  and the other passing along the rear air duct  52  to the slot-like opening  62 . 
     As the airflow passes along the air ducts  50 ,  52 , it divides into a plurality of airflow portions and flows past the vanes  100  located in each air duct  50 ,  52 . The noise emitted by the motor is attenuated by the fact that the distance between the vanes  100  and the walls of the ducts  50 ,  52 , and between the vanes  100  themselves, is restricted to a value which does not exceed the half-wavelength of the sound waves of the noise. 
     The airflow is ejected from the slot-like openings  60 ,  62  in the form of very thin, stratified sheets of high velocity, high pressure air. As the airflows leave the slot-like openings  60 ,  62 , the air pressure is at least 15 kPa and preferably approximately 20 to 23 kPa. Furthermore, the speed of the airflow leaving the slot-like openings  60 ,  62  is at least 80 m/s and preferably at least 100 or 150 m/s, more preferably approximately 180 m/s. Because the size of the slot-like opening  62  located at the end of the rear duct  52  is greater than the size of the slot-like opening  60  located at the end of the front duct  50 , a larger volume of air is emitted from the duct  52  than from the duct  50 . This provides a greater mass of air for drying the backs of the user&#39;s hands which is advantageous. 
     The two thin sheets of stratified, high velocity, high pressure air are directed towards the surfaces of the user&#39;s hands which, during use, are inserted fully into the cavity  30  and are subsequently withdrawn from the cavity  30  via the cavity entrance  32 . As the user&#39;s hands pass into and out of the cavity  30 , the sheets of air blow any existing water off the user&#39;s hands. This is achieved reliably and effectively because of the high momentum of the air leaving the slot-like openings  60 ,  62  and because the airflow is evenly distributed along the length of each slot-like opening  60 ,  62 . 
     Each stratified sheet of air is directed towards the wall of the cavity  30  which is remote from the slot-like opening through which the respective sheet of air is emitted. Because the slot-like openings  60 ,  62  are also inclined towards the lowermost end of the cavity  30 , the emitted airflows are directed into the cavity  30 . This reduces the risk of turbulent air movement being felt by the user outside the casing, e.g. in the user&#39;s face. 
     It is envisaged that it will take only a small number of “passes” of the hand dryer described above to dry a user&#39;s hands to a satisfactory degree. (By “pass”, we mean a single insertion of the hands into the cavity and subsequent removal therefrom at a speed which is not unacceptable to an average user. We envisage that a single pass will have a duration of no more than 3 seconds.) The momentum achieved by the airflows is sufficient to remove the majority of water found on the surface of the user&#39;s hands after washing during a single pass. 
     The water removed by the airflows is collected inside the cavity  30 . Each airflow will rapidly lose its momentum once it has passed the user&#39;s hands and the water droplets will fall to the lower end of the cavity  30  under the forces of gravity whilst the air exits the cavity  30  either through the cavity entrance  32  or via the open sides of the cavity  30 . The water, however, is collected by the drain  38  and passed to a reservoir (not shown) where it is collected for disposal. The reservoir can be emptied manually if desired. Alternatively, the hand dryer  10  can incorporate some form of water dispersal system including, for example, a heater for evaporating the collected water into the atmosphere. The means by which the collected water is dispersed does not form part of the present invention. 
     In an alternative embodiment, the slot-like openings  60   a ,  62   a  can be arranged so that the sheets of air which are emitted therefrom are directed generally along planes which are substantially parallel to one another. This minimises the amount of turbulent flow present inside the cavity  30  whilst the drying apparatus is in use. 
     The invention is not intended to be limited to the precise detail of the embodiment described above. Modifications and variations to the detail which do not alter the scope of the invention will be apparent to a skilled reader. For example, the shape of the cavity  30  and its entrance  32  may be altered without departing from the essence of the present invention. Also, the operational speed of the motor is not limited to the value given above but can be selected to provide the most suitable flowrate of air within the dryer.