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, and a motor arranged to drive the fan. At least one opening communicates with the fan and is arranged in the casing to direct an airflow transversely across the cavity. The motor has a rotor which, in use, rotates at a speed of at least 80,000 rpm. This produces a high velocity, high pressure airflow which dries an object efficiently and quickly and is suitable for use in a hand dryer.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of International Application No. PCT/GB2006/002119, filed Jun. 15, 2006, which claims the priority of United Kingdom Application Nos. 0515749.0, filed Jul. 30, 2005, and 0600879.1, filed Jan. 17, 2006, the contents of which prior applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    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 
       [0003]    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 2002-34835A and JP 2002306370A. However, in practice it is very difficult to achieve an airflow of sufficiently high momentum to dry the user&#39;s hands efficiently in an acceptably short length of time. The prior art does not achieve this. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the invention to provide drying apparatus which, in use, emits an air jet through an opening which is capable of drying an object in a short time as compared to the prior art. It is another object to provide a hand dryer which is capable of drying the user&#39;s hands in a short time in comparison to the prior art. It is a further object of the invention to provide an improved hand dryer in which the drying efficiency is improved in comparison to the prior art. 
         [0005]    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 arranged to drive the fan, and at least one opening communicating with the fan and arranged in the casing so as to direct an airflow transversely across the cavity, wherein the motor has a rotor which, in use, is capable of rotating at a speed of at least 80,000 rpm. 
         [0006]    By providing a very high speed motor to drive the fan, the momentum of the airflow emitted through the opening is greatly increased in comparison to that of the prior art devices. This increases the efficiency of the dryer by virtue of the fact that more water is blown from the object during each pass thereof through the airflow exiting the slot-like openings. 
         [0007]    Preferably, the rotor is capable of rotating at a speed of at least 100,000 rpm. More preferably, the motor is a switched-reluctance motor. This preferred arrangement provides the airflow with a particularly effective level of momentum. 
         [0008]    In a preferred embodiment, a hand dryer has a pair of opposed slot-like openings arranged to direct an airflow across the cavity. The preferred width of the slot-like openings is no more than 0.5 mm. Such an arrangement has been found to be highly effective in producing a hand dryer which is capable of drying a user&#39;s hands effectively and quickly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    An embodiment of the invention in the form of a hand dryer will now be described with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  is a side view of a hand dryer according to the invention; 
           [0011]      FIG. 2  is a perspective view of the hand dryer of  FIG. 1 ; 
           [0012]      FIG. 3  is a side sectional view of the hand dryer of  FIG. 1 ; 
           [0013]      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 ; 
           [0014]      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 ; 
           [0015]      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 ; 
           [0016]      FIG. 7   a  is a plan view of the cavity entrance of a hand dryer according to a second embodiment of the invention; and 
           [0017]      FIG. 7   b  is a front view of the slot-like opening located in the rear wall of the cavity of the hand dryer of  FIG. 7   a.    
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    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 . 
         [0019]    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. 
         [0020]    As shown in  FIG. 3 , a motor  39  is located inside the casing  12  and a fan  40 , which is driven by the motor  39 , is also located inside the casing  12 . The motor  39  is a brushless switched-reluctance motor and 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 . 
         [0021]    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 . 
         [0022]      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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    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  39  to drive the fan  40 . The motor  39  has a rotor which is then driven at a very high speed, namely at a speed of at least 80,000 rpm and preferably at a speed of at least 100,000 rpm. The fan  40  is thus rotated at a similarly very high speed 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 . 
         [0026]    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. 
         [0027]    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 . 
         [0028]    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, eg in the user&#39;s face. 
         [0029]    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. 
         [0030]    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. 
         [0031]    In an alternative embodiment shown in  FIGS. 7   a  and  7   b  the slot-like openings are not of constant width across the length L of the cavity of the hand dryer.  FIG. 7   a  shows a plan view of the cavity entrance of length L. The dotted lines indicate the position and shape of the user&#39;s hands as they are normally inserted into the cavity  30  between the front and rear edges  32   a ,  32   b . The arrows  80  shown in  FIG. 7   a  indicate the direction of the airflow emitted from the slot-like openings  60 ,  62  located in the edges  32   a ,  32   b  of the cavity entrance  32 . In this embodiment the curved portions  33  of the rear edge  32   b  are symmetrical about the centre line A-A of the cavity entrance  32  with the centre portion of the rear edge  32   b  being closer to the front edge  32   a  at the centre line than at a position spaced from the centre line. The minimum distance d between the front and rear edges  32   a ,  32   b  is at the centre line. The distance between the front edge  32   a  and the rear edge  32   b  is at a maximum, D, at the mid point of each curved portion.  FIG. 7   b  shows the shape of the slot-like opening located in the rear wall of the cavity. 
         [0032]    Preferably, the width of the slot-like opening in the rear wall varies gradually, increasing towards the mid point of the opening, at centre line A-A of cavity entrance  32 . 
         [0033]    In this alternative embodiment it is preferred that the variation in width of the opening is achieved by varying the distance of the upper wall of the slot-like opening away from the lower wall, in the shape of a curve, preferably in a smoothly curving shape. More preferably the curve is symmetrical about centre line A-A of the cavity entrance  32 . Preferably the maximum width R of the opening is at centre line A-A and is 0.7 mm. 
         [0034]    Preferably, the width r is substantially constant in regions F and G with the varying width region (region E in  FIGS. 7   a  and  7   b ) comprising at least half the total length L of the cavity entrance, most preferably the central half. Preferably r is 0.4 mm. 
         [0035]    In region E of the hand dryer the width of the slot-like opening  62  is greater than the width of the slot-like opening  62  in regions F and G. The increase in size of the slot-like opening  62  provides a greater mass of air  80  from rear duct  52  for drying the backs of the user&#39;s hands in the thumb and forefinger area which is advantageous. The greater mass of air in region E and the momentum achieved by the airflow is sufficient to remove the majority of water found on the backs of the user&#39;s hands after washing during a single pass. 
         [0036]    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 slot-like openings describe above may be replaced by lines of individual nozzles, each of which emits a jet of air towards the object placed within the cavity.