Abstract:
A drying apparatus includes a casing and a cavity formed in the casing for receiving an object to be dried. A fan is located in the casing so as to be capable of creating an airflow, and a motor is provided in the casing for driving the fan. Ducting is provided for carrying the airflow from the fan to at least one opening arranged to emit the airflow into the cavity ( 12 ). The ducting includes at least one air duct having a wall in which perforations are provided, and a layer of sound-absorbing material is located on the external surface of the wall so as to cover the perforations. The invention is particularly suitable for use in hand dryers.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under 35 USC 371 of International Application No. PCT/GB2007/000089, filed Jan. 12, 2007, which claims the priority of United Kingdom Application No. 0600534.2, filed Jan. 12, 2006, the contents of both 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 2002-034835A 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. 
         [0004]    One way of reducing the amount of motor noise emitted by the drying apparatus is disclosed in our copending application no GB 0515754.0. In this arrangement, vanes are positioned in the ducts which carry the airflow from the motor to the slot-like openings. A further prior art arrangement is shown in JP 2003-180554, in which various box-like silencing members are positioned inside the casing of the hand dryer. 
       SUMMARY OF THE INVENTION 
       [0005]    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 further improved in comparison to prior art and known 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. 
         [0006]    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 having a wall in which perforations are provided, and a layer of sound-absorbing material is located on the external surface of the wall so as to cover the perforations. 
         [0007]    The provision of a sound-absorbing material on the outside of the perforated wall reduces the volume of aero-acoustic noise emitted by the apparatus which, in the case of a hand dryer, renders the hand dryer more comfortable to use. 
         [0008]    Preferably, the perforations in the wall are elongate and extend generally in the direction of the airflow along the air duct. More preferably, the length of each perforation is significantly larger than the width thereof. Such an arrangement provides the wall with a significant area of perforation without significantly affecting the structural strength of the wall. 
         [0009]    In one preferred embodiment, the air duct has two opposing walls with perforations being provided in each wall and the perforations are substantially aligned with one another. 
         [0010]    In a preferred embodiment, the sound-absorbing material is compressed between the wall and an outer casing, and in a still further preferred embodiment, the sound-absorbing material is a polyester-based foam. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    Embodiments of the invention, both in the form of a hand dryer, will now be described with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a side view of drying apparatus according to the invention in the form of a hand dryer; 
           [0013]      FIG. 2  is a perspective view of the hand dryer of  FIG. 1 ; 
           [0014]      FIG. 3  is a side sectional view of the hand dryer of  FIG. 1 ; 
           [0015]      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 ; 
           [0016]      FIG. 5  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; 
           [0017]      FIG. 6  is a front view of one of the walls forming part of the ducting of  FIG. 5 ; 
           [0018]      FIG. 7  is a perspective view of a pair of opposing walls forming part of the ducting of  FIG. 5 ; 
           [0019]      FIG. 8  is a schematic front view of an opening emitting airflow into the cavity and forming part of a hand dryer according to a second embodiment of the invention; and 
           [0020]      FIG. 9  is a perspective view of the ducting a forming part of the hand dryer of  FIG. 1  according to the second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    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 . 
         [0022]    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. 
         [0023]    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 . 
         [0024]    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 . Further details of the air ducts  50 ,  52  will be described below. 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. 
         [0025]    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 downstream ends of the ducts  50 ,  52  project slightly beyond the surface of the front and rear walls  34 ,  36  of the cavity  30 . This 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 ducts  50 ,  52  also reduces the risk of the sensors  64  becoming dirty and inoperative. 
         [0026]    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. 
         [0027]    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. 5 . 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 . 
         [0028]    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. 
         [0029]    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. 
         [0030]    The internal features of the air ducts  50 ,  52  will now be described in greater detail with reference to  FIGS. 3 to 7 . Each air duct  50 ,  52  has an outer casing  54  which delimits the respective air duct  50 ,  52 . The outer casing  54  is formed by a solid wall made from a plastics material or other material suitable for the manufacture of this type of component. It is the outer casing  54  which is visible in  FIG. 5 . Inside the outer casing  54 , within each branch of the ducting  90 , lies a perforated wall member  56 . One of the perforated wall members  56  is shown in  FIGS. 6 and 7 . Each perforated wall member  56  follows the shape of the outer casing  54  of the respective air duct  50 ,  52 , but has slightly smaller dimensions than the outer casing  54 . This allows the perforated wall members  56  to extend along each air duct  50 ,  52  whilst leaving a small gap between the outer casing  54  and the perforated wall member  56 . 
         [0031]    Each perforated wall member  56  has two opposing perforated walls  56   a ,  56   b  which are joined by side walls  56   c  so that the perforated walls  56   a ,  56   b  can be formed integrally with one another. Flanges  56   d  are formed at either end of the perforated wall members  56  to assist with the correct positioning of the perforated wall members  56  within the outer casings  54 . 
         [0032]    Perforations  58  are formed in each of the perforated walls  56   a ,  56   b  as shown in  FIGS. 6 and 7 . Each perforation  58  is elongate in shape and has a length which is significantly greater than its width. In the embodiment shown, the length of the majority of the perforations  58  is at least ten times the width of the respective perforation and is more preferably at least fifteen times its width. This arrangement provides an advantage in that the total area of the perforations  58  is relatively large whilst the strength of the perforated wall member  56  is maintained. Each end of each perforation  58  is generally semi-circular in shape. 
         [0033]    It will also be seen from  FIGS. 6 and 7  that the arrangement of perforations in each perforated wall  56   a ,  56   b  is such that each elongate perforation  58  extends generally in the same direction of the airflow along the relevant air duct  50 ,  52 . Specifically, the perforations  58  closest to the centre of the perforated wall member  56  extend generally parallel to the axis  57  thereof, whilst the perforations  58  further from the centre of the perforated wall member  56  are inclined so as to lie at an angle to the axis  57 . 
         [0034]    The perforations  58  formed in each pair of opposing walls  56   a ,  56   b  are arranged so as to be aligned with one another. More specifically, in each air duct  50 ,  52 , the perforations in the innermost perforated wall  56   a  are aligned with the perforations  58  in the outermost perforated wall  56   b . By “aligned”, we mean that, at any point along the respective air duct  50 ,  52 , the positions of the perforation  58  in the opposing walls match one another. 
         [0035]    The perforations  58  extend substantially all the way along each perforated wall  56   a ,  56   b  between the flanges  56   d  at each end of the perforated wall member  56 . 
         [0036]    The gap formed between the outer casing  54  of each air duct  50 ,  52  and the adjacent perforated wall  56   a ,  56   b  is filled with a sound-absorbing material  59 . In effect, the sound-absorbing material  59  is sandwiched between the outer casing  54  and the relevant perforated wall  56   a ,  56   b . In this embodiment, the sound-absorbing material  59  is a polyester-based foam, for example, a polyester polyeurythane foam of 30 to 35 kg/m 3  density and with a cell size of 50 to 65 PPI (pores per inch). Other advantageous characteristics include a compression set of at least 10% and high thermal tolerance. A suitable sound-absorbing material is sold under the brand name Fireflex S305. Other foam materials having similar characteristics can also be used, as can fibrous textiles such as polyester matting, felt or kapok. Other open weave or open pore materials with appropriate characteristics can be used. 
         [0037]    The sound absorbing material  59  is provided in pads having a thickness of 5 mm. In the embodiment, the gap between the outer casing  54  and the perforated wall member  56  is 4 mm. Hence, when the pad of sound-absorbing material  59  is in position, the sound-absorbing material is compressed between the outer casing  54  and the perforated wall member  56 . This ensures that the sound-absorbing material is reliably maintained in contact with both the perforated wall  56   a ,  56   b  and the outer casing  54  so as to maximise the sound reduction in the drying apparatus. The pads of sound-absorbing material  59  are held in place in part by the flanges  56   d  located at either end of each perforated wall member  56 . 
         [0038]    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, preferably at least 25 to 27 litres per second and more preferably air is drawn into the hand dryer 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 . 
         [0039]    As the airflow passes along the air ducts  50 ,  52 , the aero-acoustic noise generated thereby is absorbed by the sound-absorbing material  59 . The sound waves are allowed to pass through the perforation in the perforated wall members  56  and into the sound-absorbing material  59 . However, since the volume between the outer casing  54  and the perforated wall member  56  is closed, the airflow remains inside the perforated wall member  56  without entering the said volume to any significant extent. 
         [0040]    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 8 kPa, preferably at least 15 kPa and preferably approximately 22 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. 
         [0041]    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 . 
         [0042]    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. 
         [0043]    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. 
         [0044]    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. 
         [0045]    The second embodiment of the invention is identical to the embodiment described above in all respects save that of the width of the slot-like opening  62  located at the end of the rear duct  52 . Whereas the width W 2  of the slot-like opening  62  is constant in the first embodiment, it is not constant in the second embodiment. A front view of the slot-like opening (shown schematically for clarity) is shown in  FIG. 8 . 
         [0046]    In this second embodiment, the lower edge  62   a  of the slot-like opening  62  is straight, as it is in the first embodiment. However, the upper edge  62   b  of the slot-like opening  62  is curved in the central area  1  thereof so that the width of the slot-like opening  62  increases from a minimum width w to a maximum width W. Outside the central area  1 , the minimum width w of the slot-like opening  62  is constant and the preferred value of the minimum width w is 0.4 mm. The preferred value of the maximum width W is less than twice the value of the minimum width w, in this case 0.7 mm. 
         [0047]    In this embodiment, the central area  1  covers substantially one half of the entire length L of the slot-like opening  62 . The distance between the upper edge  62   b  and the lower edge  62   a  begins to increase at a point approximately one quarter of the way along the slot-like opening  62  from either end thereof. The shape of the upper edge  62   b  is symmetrical and takes the form of a smooth curve having its highest point in the centre of the slot-like opening. 
         [0048]    In use, the hand dryer according to the second embodiment is capable of emitting an increased mass of air through the centre of the rear slot-like opening  62  in comparison to the first embodiment. This is advantageous because the area of the hands which is often most difficult to dry using this type of hand dryer is that around the thumbs and forefingers. The emission of an increased mass of air in that region of the hands improves the ability of the dryer to dry the hands evenly. In use however, the increased mass of air emitted may result in a greater amount of motor noise emitted by the drying apparatus. The increased noise may be unpleasant for a user. In the further preferred embodiment a silencing insert or block is positioned inside the rear slot-like opening. The effect of the blockage is to reduce the volume of aero-acoustic noise emitted by the apparatus. There is a reduction in mean noise and the performance of the apparatus in terms of emitted noise is more consistent. 
         [0049]    The features of the blocking insert  100  will now be described in greater detail with reference to  FIGS. 8 and 9 . The slot-like opening  62  is closed and blocked in the centremost area LL thereof. The insert  100  has a breath b and a width W dimensioned to fit from the upper edge  62   a  of the slot-like opening  62  to the lower edge  62   a  of the slot-like opening  62 . In use, the insert has the effects of blocking the air flow emitted from the drying apparatus in the centremost area LL. In this embodiment the insert  100  is fixed to both upper edge  62   a  and the lower edge  62   a  of the slot-like opening  62  and extends into the region immediately downstream of the opening. The insert  100  is tapered and smooth to minimise any frictional losses and suppress turbulent flow and noise generation. In use, the air flow in the centremost 10 mm portion of the slot-like opening is blocked with an insert having a breath b of 10 mm. 
         [0050]    It will be appreciated that, in this second embodiment, the width of the rear slot-like opening  62  can be varied by altering the shape of either or both edges and that the precise shape of the slot and the precise shape and form of the blocking insert are not limited to that shown in  FIG. 8  or  9 . For example, the breath b of the insert may vary from 5 mm-25 mm. For example, the insert may be formed close to the exit point of the slot-like opening only or may extend upstream and into the ducting some distance. Alternatively the insert may be used to reduce the level of noise emitted from drying apparatus having a slot-like opening with a constant width. The insert may be comprised of any material, preferably non-porous material such as plastic or skinned foam. The insert may be a separate component or may be formed with the duct itself. 
         [0051]    In a further 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. 
         [0052]    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, different sound-absorbing materials can be used, as can alternative shapes and arrangements of the elongate slots provided in the perforated walls. The thickness of the sound-absorbing material can be increased if desired, as can the amount of compression applied to the sound-absorbing material. Indeed, if space constraints allow, the gap between the perforated wall member and the outer casing of the air ducts will be made as large as possible. It will also be appreciated that the invention can be used in other forms of drying apparatus.