referring firstly to fig1 and 2 , the hand dryer 10 shown in fig1 to 6 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 fig1 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 fig3 , a fan 40 , which is driven by a motor ( not shown ), is 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 . 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 . fig4 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 fig5 and 6 . fig5 shows that the slot - like opening 60 has a width of w 1 and fig6 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 . in this embodiment , both widths w 1 and w 2 are constant across the length of each respective slot - like opening . 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 fig1 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 fig2 , 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 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 . 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 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 . 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 , eg 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 . 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 fig7 . 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 . 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 . 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 . 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 is not limited to that shown in fig7 . in a further alternative embodiment , the slot - like openings 60 , 62 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 .
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 at least one slot - like opening communicating with the fan and arranged in the casing so as to direct an airflow transversely across the cavity . the slot - like opening has a maximum width which is no greater than 0 . 8 mm . this produces a very narrow , high velocity , high pressure airflow which is capable of drying an object efficiently and quickly and is suitable for use in a hand dryer .