Drying Apparatus
The invention relates to drying apparatus which makes use of a narrow jet of high
velocity, high pressure air to dry an ohject, 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 2249026 A, 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'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 a slot-like 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.
There is provided 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, 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, wherein the slot-like opening is formed
between opposing walls which approach one another at an angle of between 10° and 20°.
In a preferred embodiment, the angle between the walls of the slot-like opening is
substantially 14°. This angle has been found to be advantageous in that the momentum of
2

the airflow emitted through the slot-like 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.
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, and
two opposing slot-like openings communicating with the fan via ducting and arranged in
the casing so as to direct an airflow transversely across the cavity, wherein the ducting
has a first cross-section in the vicinity of the fan whose dimensions are similar in all
directions and a slot-like cross-section in the vicinity of the openings, the transition
between the said cross-sections being gradual and smooth.
Preferably, the total cross-sectional area of the ducting is substantially constant between
the fan and a point immediately upstream of the slot-like openings. This minimises losses
within the ducting and enhances the efficiency of the fan.
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;
3

Figure 6 is a schematic sectional side view, shown on the same farther enlarged scale,
of the slot-like opening located in the rear wall of the cavity of the hand dryer of Figure
l;
Figure 7 is an isometric view of the ducting forming part of the hand dryer of Figure 1
shown in isolation from the other components of the apparatus;
Figure 8a is a plan view of the cavity entrance of a hand dryer according to a second
embodiment of the invention; and
Figure 8b is a front view of the slot-like opening located in the rear wall of the cavity of
the hand dryer of Figure 8 a.
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.
4

As shown in Figure 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.
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.
Each pair of walls 54a, 54b, 56a, 56b 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 Figures 5
5

and 6, then each wall 54a, 54b, 56a, 56b lies at an angle of substantially 7° to the
respective axis 70. Thus the angle formed between each pair of walls 54a, 54b, 56a,
56b is thus substantially 14°. This angle has been found to be advantageous, although it
could be varied by several degrees. Angles of between 10° and 20° 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'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
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-reduc.es.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 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 Figure 7.
6

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.
7

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 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 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
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 fully 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.
8

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.
If 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.
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, 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 miriirnises the amount of turbulent flow
present inside the cavity 30 whilst the drying apparatus is in use.
9

In a further alternative embodiment shown in Figures 8a and 8b the slot-like openings
are not of constant width across the length L of the cavity of the hand dryer. Figure 8 a
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 8a 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 rninimurn 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 8b shows the shape of the slot-like opening located in the rear
wall of the cavity.
Preferably, the width- of the. slot Jike_ 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
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 8a and 8b) 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-
10

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 embodiments
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.
11

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, and two opposing
slot-like openings communicating with the fan via ducting and arranged in the casing so
as to direct an airflow transversely across the cavity, wherein the ducting has a first
cross-section in the vicinity of the fan whose dimensions are similar in all directions and
a slot-like cross-section in the vicinity of the openings, the transition between the said
cross-sections being gradual and smooth,
2. Drying apparatus as claimed in claim 1, wherein the total cross-sectional area of
the ducting is substantially constant between the fan and a point immediately upstream
of the slot-like openings.
3. Drying apparatus as claimed in claim 1 or 2, wherein the ducting is divided into
two separate airflow paths at a point downstream of the fan.
4. Drying apparatus as claimed in any one of the preceding claims, wherein the
width of the or each slot-like opening is no more than 0.5 mm.
5. • Drying apparatus as claimed in any one of the preceding claims, wherein the fan
is adapted to cause an airflow to be emitted through the or each slot-like opening at a
velocity of at least 80 m/s.
6. Drying apparatus as claimed in claim 6, wherein the fan is adapted to cause an
airflow to be emitted through the slot-like opening at a velocity of at least 100 m/s.
7. Drying apparatus as claimed in any one of the preceding claims, wherein the fan
is adapted to cause an airflow to be emitted through the or each slot-like opening at a
pressure of at least 8 kPa.
11

8. Drying apparatus as claimed in claim 7, wherein the fan is adapted to cause an
airflow to be emitted through the or each slot-like opening at a pressure of at least 12
kPa.
9. Drying apparatus as claimed in any one of the preceding claims, wherein the
drying apparatus is a hand dryer.
10. Drying apparatus substantially as hereinbefore described with reference to the
accompanying drawings.
Dated this 30th day of January, 2008.

13

The invention provides drying apparatus (10) having 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, and at least one slot-like opening (60, 62) communicating with the
fan (40) and arranged in the casing (12) so as to direct an airflow transversely across the
cavity (30). According to the invention, the slot-like opening (60, 62) is formed between
opposing walls (54a, 54b, 56a, 56b) which approach one another at an angle of between
10° and 20°. In another aspect of the invention, two slot-like openings (60, 62) are
provided and a ducting (90) providing communication between the fan (40) and the slot-
like openings (60, 62) has a first cross-section in the vicinity of the fan (40) whose
dimensions are similar in all directions and a slot-like cross-section in the vicinity of the
openings (60, 62), the transition between the said cross-sections being gradual and
smooth.