Note: Descriptions are shown in the official language in which they were submitted.
3 ~ ~ ~
FIELD 0~ THE INVENTION
THIS INVENTION relates to a hot air drier and is more specifically
concerned with apparatus for providing a stream of hot unsaturated
air which may be used, for example, for body drying, or for clothes
drying.
STATE OF THE ART
Hot air driers usable either for body drying or for clothes drying
are described and illustrated in United Kingdom Patent Application
Nos. 2,222,944; 2,020,970; 2,243,546; 2,140,295 2,146,522; United
States Patent Nos~ 3,418,452; 2,977,455; 3,621,199; 4,685,222;
3,878,621; 4,756,094; 3,449,838; 3,128,161; Patent Co-operation
Treaty International Patent Application Nos. WO 80/01872;
WO/91/07900; WO 91/05503; and finally Australian published Patent
Application No. AU-A-11175/88.
All of the above driers use a blower to provide the air stream and
an electric heating element through which the air is passed prior
to delivery to the point of use. This may be a shower cubicle in
the case of a body drier, or a rack on which clothes are draped,
in the case of a clothes drier.
In order to dry wet objects, the water to be dried off must first
be raised to its evaporation temperature, and then the latent heat
of evaporation must be provided to convert the water into steam~
This is accompanied by expansion, with the result that a small
amount of water generates a large amount of water vapour. When drying
is carried out in a poorly ventilated space such as a room, the
water vapour raises the temperature and humidity in the room to
¦ an often uncomfortable level. Also, condensation of the water vapour
on cooler surfaces in the room can promote dampness and rot, and
also staining of glass surfaces such as windows and mirrors. Because
of the relatively large amount of energy required to operate a
hot air drier, and the attendant inconveniences mentioned above,
electrically operated driers tend only to be used in domestic
premises for small portable items such as hair driers.
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O~JECT OF THE INVENTION
An object of this invention is the provision of improved hot air
drying apparatus.
SUMMARY OF THE INVENTION
In accordance with the present invention apparatus for providing
a stream of hot dry air to a confined space, comprises first means
defining a first air path leading from outside the apparatus into
the confined space, second means defining a second air path leading
from the confined space to an air outlet, an electrical heater in
the first air path, and, means for driving air through at least
one of said paths to produce air circulation to and from the confined
space; in which apparatus a heat exchanger is provided having two
~I separate air flow passages in good heat exchange relationship, thefirst flow passage being connected in the first air path and the
second flow passage being connected in the second flow path to
extract heat from the air leaving the confined space and to use
the extracted heat to pre-heat the air flowing through the first
air path towards the confined space. The confined space may comprise
a large bag or a small shower cubicle of much the same volume. The
dimensions of the confined space will be matched to the drying
ability of the apparatus to achieve optimum drying performance.
The invention enables the fresh air being drawn into the first
air path to be pre-heated before flowing past the heating element.
The energy expended by the heating element to carry out drying is
thus reduced. In consequence, the size of the heater can be reduced,
and the running costs to carry out drying are also reduced, orl
conversely the rate of drying a given quantity of clothing can
be increased for the same running costs.
PREFERRED FEATURES OF THE INVENTION
Preferably the heat exchanger is of counter-flow type which operates
with an efficiency of between 80%-90~. A construction of heat
exchanger of this type and particularly well suited for use with
the present invention is described in the Applicant's U~ ~e~ ~t~
Patent No. 5,078,208, hereby inserted by way of reference.
Suitably the blower unit and electrical heater are contained in
the first air path downstream of the first passage and the second
air path is provided with an exhaust fan. Preferably, the exhaust
fan is located upstream of the second passage. It is preferred to
have the exhaust fan operated by a motor which also operates a second
fan located upstream of the first passage of the heat exchanger.
The motor may be controlled by a switch responsive to either the
temperature or the humidity of the air entering the second air
path attaining a pre-set level.
The motor of the fans is not operated during an initial phase of
the drying. Instead, the air in the confined space is re-circulated
through the heater so that its temperature rapidly rises to a level
at which optimum drying takes place. The motor is then switched
on to remove the humid air at drying temperature from the confined
space and simul~aneously replace it with fresh air obtained from
the first passage of the heat exchanger by way of the heating element
and blower unit.
The apparatus may include a drying assemby usable to dry clothes
and comprising a rack or a set of parallel cords which can be
erected inside the confined space. The hot air discharged into
the confined space is arranged to pass upwardly between the clothes
to absorb moisture from them. Much of the heat of the humidified
air leaving the bag is subsequently recovered by the heat exchangerO
INTRODUCTION TO THE DRAWINGS
The invention will now be described by way of examples, with
reference to the accompanying drawings, in which:-
IN THE DRAWINGS
FIGURE 1 is a perspective view of a casing of a wall-mounted
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drying cabinet showing a drying rack assembly in its stowed
position;
FIGURE 2 shows the cabinet of figure l with the drying rack
assembly in its erected horizontal position and a non-permiable
flexible bag defining a confi:ned space in which clothes drying
is to take place;
FIGURE 3 is a front view of the cabinet with the front of its
casing removed to show inter:nal detail and air paths through
the cabinet;
FIGURE 4 is a vertical section through the casing of figure
3 and taken on the line and in the direction indicated by
the arrows IV-IV in figure 3; and,
FIGURE S is a broken cross-section through figure 3 taken on
the line and in the direction indicated by the arrows V-V in
that figure, the rack assembly being omitted.
DESCRIPTION OF PREFERRED EMBODIMENT.
Figure l shows a cabinet 1 having a casing 2 to the opposite sides
of which are two arms 3 are pivoted at their upper ends at 4. The
lower ends of the arms 3 carry a box structure 5 which can be swung
forwardly to the position shown in figure 2 at which it is held by
manually-releasable latches lO.
The box structure 5 comprises a top fixed plate 6 and a vertical
plate 7 joined between the intermediate portions of the arms 3 and
having a second plate 8 pivoted to its under edge at 9. The plate
8 has a stowage position shown in figure l, at which it extends
in spaced parallel relationship to the plate 6 and an operating
position, shown in figure 2, at which it fills the space between
the plate 7 and the front face of the casing 2.
The underside of the plate 8 is provided with a set of parallel
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drying cords 11 which, when the plate 8 is in its operating position
shown in figure 2, extend horizontally beneath the plates 8 and
6 and are secured to the front edge of the plate 6 and the back
edge of the plate 80 When the plate 8 is in the stowed position
of figure 1, the cords are contained inside the cavity of the box
structure 5 provided between the plates 6,7 and 8.
A bag 12 which is normally also stowed in the box structure 5 and
which is made from a light thin plastics material, has its mouth
attachable by an easily~removable, continuous connection, such as
may be provided by a VELCR0 strip (VELCR0 is a registered trade
mark), to the outsides of the arms 8, the front of the box structure
5 and the back of the cabinet 2, as shown in figure 2. The bag 12
is about 1.8 metres high, which is sufficient to totally enclose
clothes suspended from the cords 11 for drying. The bag 12 has,
at its lower end, an outlet valve 13 to allow water dripping from
the clothes to be collected without wetting the floor beneath the
drier.
The lower front of the casing is provided with a hot-air outlet
grill 14 which is manually movable along a vertical arc so that
it discharges hot air at a desired angle between the horizontal
and the vertical. The positioning of the grill 15 is achieved by
turning a knurled wheel part of which protrudes from the front of
the cabinet alongside the grill, as shown at 15.
The casing 2 is provided above the level of the pivots 4 with an
air inlet grill 16 which may be opened or closed by a knurled knob
17 positioned alongside the grill 16. A second air inlet opening
28 is provided in the top of the casing 2 and the two inlets are
selectively openable so that closure of the grill 16 automatically
opens the inlet 28, and vice-versa. The air inlet 28 is connected
to an air inlet duct if the cabinet is sited in a shower cubicle,
so that outside ambient outside air is drawn into the cabinet
for carrying out drying, rather than air sucked into the cabine-t
through the grill 16. A humid air outlet 29 is also provided in
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the top of the casing 1 for venting to waste air which has been
used for drying.
The casing 2 is provided beneath the level of the pivots 4 with
a second air inlet grill 19 which extends parallel to the grill
16 and is positioned so that it lies in the upper zone of the
confined space enclosed within the bag 12, to suck ~ot humid air
out of the bag.
Figures 3, 4 and 5 show the interior of the casing.
Hot air is provided to the grill 14 from a cowl 20 which receives
air from a tangential flow fan 21. The fan 21 draws air through
an electrically-operated heater 22 comprising two, independently-
operated heating elements each of 0.9 kilowatts rating. This air
may come from an outlet manifold 24 of a heat exchanger 25, or,
by way of an aperture 26 in the cowl 20, from a plenum 27 provided
on its outside with the inlet grill l9.The inlet of an air passage
30 of the heat exchanger 25 opens through a manifold 48 into the
plenum 27. the outlet end of the air passage 30 is referenced 31
and opens into one compartment 32 of a chamber 60 formed in the
upper end of the casing 2 and divided by a partition 61 into two
compartments 32,33 respectively. The outlet 29 leads out of the
compartment 32 to an exhaust.
As shown in figure 3, a motor 40 drives two fans or impellers 41
and 42. The impeller 41 is arranged at the air inlet manifold 48
to drive air from the plenum 27 into the air passage 30 of the heat
exchanger 25. The second impeller 42 is mounted in a space 50
provided with the grid 16 and communicating selectively with the
openings in the grid 16 and the air inlet 28, the choice being
effected by operation of the switch 17 (see figure 1).
The impeller 42 operates to draw air from the space 50 into a second
passage 45 of the heat exchanger 25. The heat exchanger is of
counterflow type. It comprises a stack of parallel pockets each
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containing a platen of almost identical parallel gas flow
passageways. The gas flow through neighbouring pockets is almost
in true counterflow. The gas inlets and outlets to the passageways
are arranged on adjacent sides of two corner regions of the heat
exchanger stack. Tests have shown that such a construction of hea-t
exchanger is easy and cheap to manufacture and will provide a thermal
efficiency of 80% or more.
The second compartment 3~ of the chamber 60 communicates with the
space 50 by way of an opening closable by operation of the switch
17 so that the impeller 50 either draws in air from the inlet 18,
or from the grill 16. The compartment 34 also communicates through
a channel 63 arranged between one side of the casing 2 and the heat
exchanger 25, with a further compartment 65 in which is mounted
ii a motor 66 driving the radial fan 21. The channel 63 provides cooling
air to the motor 66.
A temperature or humidity detector 70 is mounted in the plenum 27.
This controls operation of the motor 40 and switches it on, if the
temperature of the air entering the plenum 27 is higher than a pre-
set value. When the cabinet is operating as a drier, this temperature
is conveniently about 50 Centigrade. If the detector is responding
to humidity, it switches on the motor 40 when the humidity rises
to about 85~. A further temperature sensor 71 is provided adjacent
the air entry side of the cowl 20 to swi-tch off the heater 22 if
the air temperature exceeds a pre-determined but adjustable value.
OPERATION OF THE THE PREFERRED EMBODIMENT
,j With the cabinet in the configuration shown in figure 1 it may be
! used as a space heater. the motor 66 and the heater 22 are operated
but the motor 40 is not. The fan 21 then sucks air from the grill
19 by way of the plenum 27 and the opening 26, and delivers the
heated air through the grill 14 in the required direction. The
temperature in the room is maintained at a chosen value by the sensor
71.
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If the cabinet is to be used to dry clothes, the arms 3 are raised
from the position shown in Eigure 1 to the position shown in figure
2. The plate 8 is turned about its hinge 9 so that the space between
the arms 3 and the casing 2 is blanked off by the plates 6,7 and
8 which provide an effective ceiling to the bag 12. The movement
of the plate 8 automatically exposes the grid of suspension cords
11 over which the clothes to be dried are draped. The bag 12 is
then liung in the position shown in figure 2 to enclose the clothes
completely so that there is virtually no escape of air from within
the bag 12 otherwise than through the cabinet 1.
Drying of the clothes takes place in two phases. In the first phase
the motor 66 and the heating element 22 are energised. As the
temperature and humidity of air initially drawn out from the bag
i! 12 are l~w, as the clothes are usually cold and wet, the motor 40
is not operated. Air is then drawn out of the bag 12 via the grill
19 and flows through the opening 26 into the upper end of the cowl
20. This ~ir is re-circlllal:o(l rol)oalodly througll Lhe hag an~l hcater
so that its temperature and humidity rapidly rises to the point
at which the detector 70 responds. Although the re-circulated air
expands during heating, very little of the volume increase escapes
into the surrounding room, as the passages through the heat exchanger
25 remain open.
~hen the detector 70 responds to the temperature or humidity in
the air attaining the pre-set value, it operates the motor 40. The
impellers 41,42 then force air through the ~primary and secondary
passages 30 and 45 of the heat exchanger 25. As the two impellers
are identical and are driv~en at the same speed, they produce
substantially the same air flow through each of the passages. As
I is clear from figure 3, the passage 45 supplies air from either
the grill 16 or the inlet 28 to the heater 22 and the fan 21.
Simultaneously the passage 30 carries hot saturated air drawn into
the plenum 27 to the outlet 29. As the two passages are in
counterflow antl in good heat exchange relationship, the incoming
air is preheated by heat extracted from the outgoing air~ so that
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the heating element 22 only has to provide the thermal losses of
the heat exchanger 25. Its rating necessary to maintain the drying
temperature is thus very much less than would be the case were the
heat exchanger not present.
For optimum drying, the grill 1~ should be turned to the position
shown in figure 2, at which it directs air into the lower part of
the bag 12. This not only assists in maintaining the shape of the
bag, but ensures that the hot and relatively dry air flows upwardly
between the clothes on the cord rack. These clothes extend in
vertical rows parallel to the cords 11 so that the hot air flows
evenly past both sides of the clothes before entering the grill
19 of the cabinet. Rapid and effective drying is thus ob-tained.
Should the clothes be very wet when placed in the drier, they will
inevitably drip into the bag 12. Some of this drip water will
evaporate from the bag during operation of the drier. The remainder
can be removed by operating the valve 13.
I~hen drying is completed, the bag is opened by detaching its mouth
and the clothes are taken from the rack assembly. The plate 8 is
then released and turned about its hinge so that the cords 11 are
once again contained in the box structure 5. The catches 10 holding
up the arms 3 are then released and the arms 3 swung dowll to the
positions shown in figure l.
It will be noticed that -the cabinet described can be used as a space
heater, or it may be used in its space-heating configuration in
a shower cubicle to perform body drying. If the cabinet is to be
used for c]othes drying, such drying takes place without any
f significant escape of hot humidified air into the surrounding room.Thus many of the objectionable characteristics of currently available
clothes drying cabinets are avoided. If the cabinet is mounted in
a shower cubicle having a door, the use of a bag 12 is still
preferred as the effectiveness of drying is a function of the volume
of the confined space. As long as the confined space is matched
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to the characteristics of the apparatus, optimum and therefo~ J 2
drying conditions can be obtained. Very often a shower cubicle will
have a volume substantially` larger than that of the bag and in such
a situation drying of clothing will inevitably take place more
slowly, unless the bag 12 is used.
The use of the inlet 28 as an alternative to the grill 16 allows
outside air from an external source to be preheated in the heat
exchanger,rather than partially saturated air from a shower cubicle
in which the cabinet may be mounted providing the fresh air supply.
In one example of a drier constructed as described above, the
following particulars were present:
Cabinet was 500mm. high, its depth was 150rnm. and its width was
;!1 600mm. The depth of the cabinet with the arms extended hori~ontally,
as shown in figure 2, was 700mm
The motor 40 was rated at 80 wat-ts, and the motor 66 was rated at
80 watts. The fan was a TORIN tangential fan delivering 100 litres
of air per second. The impellers 41~42 each delivered 50 litres
per second of air. the lleating element 22 has two separately operable
0.9kilowatt heating elements. During the initial phase of drying,
both elements are operated. Once the motor 40 is operated the second
phase of drying commences, keeping the heat high and the air
saturated when it leaves the bag 12. ~hen the humidity drops below
a predetermined level which signifies that the clothes are nearly
dry, the heating element is reduced from 1.8 kilowatts to 0.9
kilowatts. This saves energy while maintaining a lligh rate of drying.
The compartment 65 is hermetically sealed from the interior of the
I cowl 21 so that the motor 66 is unaffected by the temperature of
air flowing through the cowl 20.
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