Drying Apparatus
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.
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's hands efficiently in an
acceptably short length of time. The prior art does not achieve this.
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'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.
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.
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
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is blown from the object during each pass thereof through the airflow exiting the slot-
like openings.
Preferably, the rotor is capable of rotating at a speed of at least 100,000 rprh. More
preferably, the motor is a switched-reluctance motor. This preferred arrangement
provides the airflow with a particularly effective level of momentum.
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 0.5mm. Such an arrangement has been found to be highly
effective in producing a hand dryer which is capable of drying a user's hands effectively
and quickly. .
An embodiment of the invention in the form of a hand dryer will now be described with
reference to the accompanying drawings, in which:
Figure 1 is a side view of a hand dryer according to the invention;
Figure 2 is a perspective view of the hand dryer of Figure 1;
Figure 3 is a side sectional view of the hand dryer of Figure 1;
Figure 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 Figure 1;
Figure 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 Figure 1;
Figure 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 Figure
i;
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Figure 7 a is a plan view of the cavity entrance of a hand dryer according to a second
embodiment of the invention; and
Figure 7b is a front view of the slot-like opening located in the rear wall of the cavity of
the hand dryer of Figure 7a.
Referring firstly to Figures 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 Figures 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'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 Figure 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
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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 wail 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.
Figure 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 54a, 54b of the air duct 50 converge to form
the slot-like opening 60 and the walls 56a, 56b of the air duct 52 converge to form the
slot-like opening 62. Even greater detail can be seen in Figures 5 and 6. Figure 5
shows that the slot-like opening 60 has a width of Wl and Figure 6 shows that the slot-
like opening 62 has a width of W2. The width Wl of the slot-like opening 60 is smaller
than the width W2 of the slot-like opening 62. The width Wl is 0.3mm and the width
W2 is 0.4mm.
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'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's hands are introduced to the cavity 30. As
can be seen from Figures 1 and 3, the walls 54a, 54b, 56a, 56b 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 54a, 54b, 56a, 56b of the ducts 50, 52 reduces the
tendency of the user's hands to be sucked towards one or other of the walls 34, 36 of the
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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 54a, 54b,
56a, 56b of the ducts 50, 52 also reduces the risk of the sensors 64 becoming dirty and
inoperative.
As can be seen from Figure 2, the shape of the cavity entrance 32 is such that the front
edge 32a is generally straight and extends laterally across the width of the hand dryer
10. However, the rear edge 32b 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
32b 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 32a, 32b of the cavity entrance 32 is that, when a user's hands are inserted into
the cavity 30 through the cavity entrance 32, the distance from any point on the user'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's
hands are first inserted into the cavity 30 through the cavity entrance 32, the sensors 64
detect the presence of the user'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.otb.er
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
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openings 60, 62, the air pressure is at least 15kPa and preferably approximately 20 to 23
lcPa. 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
180m/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's hands which is
advantageous.
The two thin sheets of stratified, high velocity, high pressure air are directed towards the
surfaces of the user's hands which, during use, are inserted folly into the cavity 30 and
are subsequently withdrawn from the cavity 30 via the cavity entrance 32. As the user's
hands pass into and out of the cavity 30, the sheets of air blow any existing water off the
user'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'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'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's hands after
washing during a single pass.
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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'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 shown in Figures 7a and 7b the slot-like openings are not
of constant width across the length L of the cavity of the hand dryer. Figure 7a shows a
plan view of the cavity entrance of length L. The dotted lines indicate the position and
shape of the user's hands as they are normally inserted into the cavity 30 between the
front and rear edges 32a, 32b. The arrows 80 shown in Figure 7a indicate the direction
of the airflow emitted from the slot-like openings 60, 62 located in the edges 32a, 32b of
the cavity entrance 32. In this embodiment the curved portions 33 of the rear edge 32b
are symmetrical about the centre line A-A of the cavity entrance 32 with the centre
portion of the rear edge 32b being closer to the front edge 32a at the centre line than at a
position spaced from the centre line. The minimum distance d between the front and
rear edges 32a, 32b is at the centre line. The distance between the front edge 32a and
the rear edge 32b is at a maximum, D, at the mid point of each curved portion. Figure
7b shows the shape of the slot-like opening located in the rear wall of the cavity.
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.
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
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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 0.7mm.
Preferably, the width r is substantially constant in regions F and G with the varying
width region (region E in Figures 7a and 7b) comprising at least half the total length L
of the cavity entrance, most preferably the central half. Preferably r is 0.4mm.
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'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's hands after washing
during a single pass.
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.
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We claim:
1. 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, at least one opening communicating with the fan and arranged in the
casing so as to direct an airflow transversely across the cavity, the opening comprising a
pair of opposed slot-like openings, wherein the motor has a rotor which, in use, is
capable of rotating at a speed of at least 80,000 rpm.
2. Drying apparatus as claimed in claim 1, wherein the rotor is capable of rotating
at a speed of at least 100,000 rpm.
3. Drying apparatus as claimed in claim 1 or 2, wherein the motor is a switched-
reluctance motor.
4. . Drying apparatus as claimed in claim 4, wherein the width of each slot-like
opening is no more than 0.5 mm.
5. Drying apparatus as claimed in claim 5, wherein, in use, the velocity of the
airflow emitted through the slot-like opening is at least 100 m/s.
6. Drying apparatus as claimed in any one of the preceding claims, wherein, in use,
the pressure of the airflow emitted through the slot-like opening is at least 15 kPa.
7. Drying apparatus as claimed in any one of the preceding claims, wherein, in use,
the pressure of the airflow emitted through the slot-like opening is at least 20 kPa.
8. Drying apparatus as claimed in any one of the preceding claims, wherein the
drying apparatus is a hand dryer.
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9. Drying apparatus substantially as hereinbefore described with reference to the
accompanying drawings.
Dated this 6th day of February, 2008.

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Drying apparatus (10) has a casing (12), a cavity (30) formed in the casing (12) for
receiving an object, a fan (40) located in the casing (12) and capable of creating an
airflow, a motor (39) arranged to drive the fan (40). At least one opening (60, 62)
communicates with the fan (40) and is arranged in the casing (12) so as to direct an
airflow transversely across the cavity (30). According to the invention, the motor (39) has
a rotor which, in use, is capable of rotating at a speed of at least 80,000 rpm. This
produces a high velocity, high pressure airflow which is capable of drying an object
efficiently and quickly. The invention is suitable for use in a hand dryer.