[0001] The present invention relates to a closed cycle dryer comprising a heating unit used
to heat the air that is blown in a rotating drum and a condensing unit upstream the
heating unit comprising an air-cooled heat exchanger where the hot and humid air downstream
the drum is contacting a first side of a wall, a second side of said wall of the heat
exchanger being contacted by flowing air at ambient temperature. The present invention
relates also to washing-drying machine in which the laundry can be washed and then
dried in the same appliance. With the term "wall" referred to the heat exchanger we
mean the heat exchanging surface which may comprises actually several tubes or plates.
[0002] In this kind of domestic dryer for drying laundry (after washing and spinning thereof)
the condensing unit is used to remove moisture which condenses on the first side of
the exchanging surface and is collected in a water reservoir or container. In such
dryers the process air runs in a closed loop. The thermal connection to the ambient
air takes place through the wall of the heat exchanger. Process air and cooling air
are not mixed.
[0003] It is well known the importance of providing the customers with appliances which
are very efficient in order to reduce energy consumption. This is particularly true
for dryers where all the components of the appliance, particularly the heater, require
a high level of energy compared to other appliances.
[0004] It is therefore an object of the present invention to provide a closed cycle air-condensing
dryer which has better performance in term of energy saving.
[0005] The applicant has discovered a simple way of reducing energy consumption of around
2% or more without impacting adversely other performance characteristics of the appliance.
Moreover the solution according to the invention has also other advantages since it
decreases the drying cycle time and increases the condensation efficiency by about
11 % and 15% respectively.
[0006] The above object and further advantages are reached thanks to the features listed
in the appended claims.
[0007] According to the invention, at least a portion of the heat exchange surfaces is provided
with holes through which a controlled portion of hot and humid air coming from the
rotating drum can be exhausted.
[0008] Further advantages and features according to the present invention will be disclosed
in the following detailed description, provided as a non limiting example, with reference
to the attached drawings in which:
- figure 1 is a schematic view of a closed cycle dryer according to the invention;
- figure 2 is a perspective view of a component used in the dryer of figure1;
- figure 3 is a top view of the component of figure 2 according to a second embodiment
of the invention; and
- figure 4 is a table showing the results of the invention compared to a known dryer.
[0009] With reference to the drawings, with 10 is indicated the rotating drum of a closed
cycle dryer which is fed in 10a with hot air downstream a heater 12. The still hot
and humid air is exhausted in 10b from the drum 10 and, after a filter 18, is blown
by a fan 14 though a condensing unit 15 provided with an air-cooled heat exchanger
16. The dry and cooled air 22 is then re-circulated to the drum 10. The heat exchanger
16 presents a wall 17 having two sides. A first side 17a is contacted by the hot and
humid air 13 coming from the drum 10 while a second side 17b is contacted by air 19
at ambient temperature.
[0010] Process and ambient air are divided by the walls of the heat exchanger where condensation
takes place.
[0011] According to the invention, the wall 17 is provided with holes 21 though which a
portion of the hot and humid air (and therefore a not-condensed portion of the water
vapor) can be directly exhausted to the ambient. Already condensed vapor (liquid)
can also be exhausted and will be re-evaporated on the cooling side of the heat exchanger.
Condensing and re-evaporating on the cold side will be in a zero energy balance. By
using a predetermined number and diameter of holes 21 allows adjusting condensation
efficiency, energy consumption and drying time. With the given holes the adjustment
of the mentioned values are fixed. Not condensing completely the steam leads to an
improvement of drying time and energy consumption.
[0012] In figure 2 it is shown a detail of the air-cooled heat exchanger 16 where the exchange
surface or wall 17 is defined by a plurality of flattened and stacked tubes 24 where
a defined distance between each couple of tubes is maintained. The heat exchanger
16 is of the removable type for cleaning purposes. In the example shown in figure
2, four tubes are used and only the upper tube is provided with circular holes 21.
Such holes are preferably located sidewise near the end 24a of the tube 24 which is
close to the cooling air entrance indicated with reference 26.
[0013] The number and dimension of the holes can vary in a quite broad range, but good results
have been obtained by providing each tube 24 with from 2 to 15 holes having a diameter
from 2 to 8 mm for a total cross section area comprised between 1 and 2 cm
2.
[0014] Through holes 21 in the heat exchanger 16 hot and humid air and condensed water can
be sucked helping by re-evaporation to condense steam. Moreover process air can be
exhausted out of the circulation pattern without condensing due to the presence of
enough heated up air on the cold side of the heat exchanger.
[0015] The direct effect of providing the heat exchanger with holes 21 can be viewed in
figure 4 which referrer to the same closed cycle dryer, one without holes (prior art)
and the other with holes. It is clear how the simple use of holes in the heat exchanger
wall can provide advantages in terms of time cycle reduction (from 135 minutes to
120 minutes), condensation efficiency (from 84 to 71%, bearing in mind that lower
condensation efficiency leads to shorter drying time and smaller energy consumption),
and energy consumption (from 0,546 kW/kg to 0,536 kWh/kg).
[0016] In figure 3 it is shown a second embodiment where the holes 21 can be opened and
closed by the customer with levers 30 (acting as rotating locks) that are mounted
on each flattened tube or plate 24. If the customer opens the holes 21 the process
is accelerated and the condensation is reduced and also the energy consumption as
well. With the levers 30 the holes 21 can be opened or closed to adjust humidity that
will be lead out to ambient.
[0017] Instead of manual adjustment of the lever 30, the dryer can be provided with an electronic
control for automatically adjusting the total free area of the holes 21 depending
on the drying cycle chosen by the user and by the actual working condition of the
appliances (for instance load of laundry, water content thereof, ambient temperature
etc.).
[0018] A porous material or a kind o filter can be inserted into the holes 21 in order to
avoid lint entering the cold air flow and accumulate on the cold air flow side.
1. A closed cycle dryer comprising a heating unit (12) used to heat the air that is blown
in a rotating drum (10) and a condensing unit (15) upstream the heating unit comprising
an air-cooled heat exchanger (16) where the hot and humid air (13) downstream the
drum is contacting a first side (17a) of wall (17), a second side of said wall (17)
of the heat exchanger being contacted by flowing air (19) at ambient temperature,
characterized in that at least a portion of said wall (17) is provided with apertures (21) where a portion
of the hot and humid air can be exhausted.
2. A closed cycle dryer according to claim 1, wherein said air-cooled heat exchanger
(16) presents a plurality of flattened tubes (24) in which ambient air is adapted
to flow, the outside surface of said tubes (24) being in contact with the hot and
humid flowing air.
3. A closed cycle dryer according to claim 2, wherein the hot and humid hot air is flowing
in a direction substantially crossing the direction of ambient air, or in a counter
flow or in a parallel flow.
4. A closed cycle dryer according to claim 2 or 3, wherein said flattened tubes (24)
are stacked.
5. A closed cycle dryer according to any of claims 2 to 4, wherein the apertures (21)
are provided close to a first end of tubes (24) where ambient air is entering.
6. A closed cycle dryer according to any of claims 2-5, wherein a device (30) is provided
for adjusting the free area of the apertures (21).
7. A closed cycle dryer according to claim 6, wherein such device is a lever (30) pivoting
on the flattened tube (24) and adapted to close/open the apertures (21) thanks to
rotation thereof.
8. A closed cycle dryer according to any of the preceding claims, wherein the total area
of the apertures (21) is comprised between 1 and 2 cm2.
9. A closed cycle dryer according to any of the preceding claims, wherein the apertures
(21) are provided with a porous material in order to filter lint.