EP3234255B1

EP3234255B1 - Laundry drying apparatus with a filter system

Info

Publication number: EP3234255B1
Application number: EP14823954.4A
Authority: EP
Inventors: Nicola Reid; Giuseppe Rossi
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2014-12-16
Filing date: 2014-12-16
Publication date: 2019-05-15
Anticipated expiration: 2034-12-16
Also published as: EP3234255A1; AU2014414436A1; AU2014414436B2; CN107002343B; CN107002343A; WO2016095970A1

Description

The invention relates to a laundry drying apparatus, in particular a dryer or washer-dryer.
DE 197 05 616 A1 discloses a laundry drying apparatus containing a heat exchanger. A filter system for filtering lint is arranged upstream of the heat exchanger. This filter system comprises two filter elements mounted at a support frame. The first filter element is a coarse filter filtering coarse lint parts whereas the second filter is filtering fine particles. This filter system shall trap even finest particles in the process drying air flow before this drying air flow is reaching the heat exchanger. The filter system is extractable out of the cabinet of the laundry drying apparatus in order to clean the fine filter from trapped lint.
The heat pump dryer of EP 2 386 679 A1 has a lint filter arranged in front of a dehumidifying unit. Flint collected on the front surface of the linter filter can be flushed away by flowing water from a nozzle to the front surface of the lint filter.
It is an object of the invention to provide a laundry drying apparatus providing an efficient and facile cleaning of a filter system arranged within a drying air channel.
The invention is defined in claim 1. Particular embodiments are set out in the dependent claims.
According to the invention, a laundry drying apparatus - in the following description also denoted in brief "apparatus" - comprises a cabinet and a laundry storing compartment arranged within the cabinet. An air channel is arranged within the cabinet and adapted to guide drying air from at least one air outlet of the laundry storing compartment. The air channel is adapted to guide the drying air to at least one air inlet of the laundry storing compartment. Preferably, the apparatus is providing a closed loop air channel such that the laundry storing compartment and the air channel form a closed loop for circulating the drying air.
Additionally, the apparatus comprises a filter system in order to trap lint removed from laundry during a drying cycle. For this purpose, the filter system is arranged within the air channel downstream the laundry storing compartment. The filter system contains a first lint filter (in brief "first filter") and a second lint filter (in brief "second filter"). Further, the apparatus comprises a heat exchanger arranged within the air channel and which is adapted to cool the drying air. The filter system is arranged upstream of the heat exchanger. According to a preferred embodiment, the upstream arrangement means that the filter system is arranged between the laundry storing compartment and the at least one heat exchanger. In one embodiment, the heat exchanger arranged in the air channel is an evaporator of a heat pump system of the apparatus and in an alternative embodiment the heat exchanger is a drying air/ambient cooling air heat exchanger of the apparatus which is used e.g. in a condensation dryer for cooling process air.
The apparatus comprises a filter wet cleaning unit which has a nozzle for supply liquid in order to wash the first filter. The nozzle is arranged such that the liquid flowing out of the nozzle is directed towards the front surface of the first filter.
The filter wet cleaning unit is adapted to preferably provide an automatic filter cleaning thus avoiding or reducing requirement for manual filter cleaning by the user over many drying cycles. The first filter is cleaned or washed very efficiently by directing liquid flowing out of the nozzle towards the front surface of the first filter.
The front surface is particularly the side of the first filter where the drying air is entering the first filter. Since lint, fluff and other particles are trapped preferably at the front surface, the first filter can be cleaned/washed efficiently in a very short time using the wet cleaning unit.
Usually, the nozzle has one or more outlets for supplying liquid. In order to support an efficient cleaning process, the at least one outlet is arranged above and/or upstream of the first filter. Thus the whole front surface of the first filter is flushed by the cleaning liquid without any additional construction measures.
In a preferred embodiment the laundry storing compartment is a drum or a rotatable drum or a drum that is rotatable around a (or a substantially) horizontal axis.
In a further embodiment the apparatus does not comprise any additional lint filter apart from the filter system. Thus any additional lint filter components to arrange within the cabinet can be avoided. In particular, it is not necessary to provide a filter component at the loading opening of the laundry storing compartment.
The first filter is configured and arranged relative to the nozzle in such a manner that the second filter is completely or substantially screened or protected from contact with liquid flowing out of the nozzle. Thus it is possible to provide a first filter type which is adapted for being wet-cleaned after every drying cycle and a second filter type adapted to provide filtering function over a high number of drying cycles. This supports the efficiency of the cleaning process and the user-friendliness of the filter system. In any design it is preferred that result of screening or shielding of liquid from the second filter by the first filter (and/or the existing average gap - see below) is that no or essentially no liquid supplied to the first filter can contact the front surface of the second filter. It should be avoided that the second filter is wetted by the cleaning liquid and thus needs to be dried - what costs additional drying energy for a laundry cleaning cycle - specifically when the second filter is a sponge (sponge-type), drying would require a long time as the water in the pores would additionally block the drying air flow.
In a preferred embodiment the filter system comprises a support structure having a first supporting position and a second supporting position. The first supporting position is adapted to support the first filter, whereas the second supporting position is adapted to support the second filter. The support structure is designed such that an air gap is formed between the first filter and second filter when both filters are placed in their supporting positions, i.e. in the first supporting position and in the second supporting position. The air gap is adapted such that the filters do not or essentially do not abut to each other. Preferably the gap is dimensioned such that the first filter is adapted to screen or to shield the second filter from contact with liquid flowing out of the nozzle, even in case some of the liquid passes from the front side of the first filter to the rear side of the first filter. Due to the gap the liquid can flow down in the gap without contacting the surface of the second filter. In case the filters essentially do not abut to each other, they may abut at an edge, for example at the upper edge. However then the gap or clearance is provided at the other or remaining areas. While providing the gap, the filters are preferably arranged in close neighborhood or arranged adjacent to each other such that the filter system is designed in a space-saving manner.
In an embodiment the filters are supported by the support structure independently of each other thus providing a user-friendly handling of the filters, e.g. if only one filter shall be detached or changed.
Preferably, the nozzle has at least one of the following features:

the nozzle is adapted to distribute the liquid over or essentially over the horizontal width of the front surface of the first filter,
the nozzle is arranged at or within the air channel relative to the first filter such as to supply the liquid to an upper region of the first filter,
the nozzle has one, two, three or more outlets adapted to direct the liquid towards the first filter,
the nozzle has at least one elongated outlet wherein the elongated extension is in parallel to the first filter surface.

Such design features of the nozzle support an efficient cleaning of the first filter along its whole filter surface.
In a further embodiment the air channel of the apparatus comprises a channel opening wherein the first and second filters are removable from the air channel through the channel opening. Preferably, the cabinet comprises a cabinet opening in such a manner that the first and second filters are removable from the air channel through the channel opening and the cabinet opening. In this regard, the filters may be removed one after the other. Alternatively, the first and second filters may be provided in a or as a filter unit of the filter system that could be simply removed as a sole/complete unit or component from the air channel.
In order to further enhance an efficient cleaning of the first filter, the liquid flowing out of the nozzle of the filter wet cleaning unit and the surface plane of the first filter may have a relative arrangement to each other to improve flushing efficiency. Preferably, the liquid flowing out of the nozzle has a first direction and the surface plane of the first filter has a second direction, wherein the first and second directions are inclined to each other by an inclination angle. Additionally or alternatively, the nozzle is oriented relative to the surface of the first filter such that the liquid flowing out of the nozzle hits or urges the surface of the first filter under an inclination angle. The value of the inclination angle is preferably at or more than 2°, 3°, 5°, 10° or in the range from 1° to 4° or 2° to 5° or 3° to 10°.
Preferably, the filter system and the first and second filters are placed in their respective operational positions in the apparatus such that the nozzle of the filter wet cleaning unit directs the liquid towards the first filter. The second filter is arranged, in relation to the nozzle, behind the first filter in a manner such that the first filter forms a screen adapted to prevent liquid flowing out of the nozzle to reach onto the surface of the second filter. As already mentioned, the first filter thus is acting in an additional function as a means for protecting the second filter against unnecessary or disturbing liquid.
Preferably, the apparatus comprises a heat pump system. Therein the heat exchanger is a first heat exchanger and a second heat exchanger is provided for heating the drying air. Thus the filter system could be applied to an apparatus having a heat pump function, in particular a heat pump dryer or heat pump washer-dryer.
In a further embodiment the filter system comprises at least one filter alignment element. This at least one element is adapted to cooperate with at least one counter-alignment element provided at the filter wet cleaning unit or at the air channel. The elements correspond or mechanically cooperate with each other such that the first filter is positionally aligned with the nozzle of the filter wet cleaning unit. The at least one filter alignment element effects accurate alignment of the filter system within the air channel. Further, this alignment causes automatically the desired relative arrangement between the filter system and the nozzle when the filter system is inserted into the operational position within the air channel. This ensures a correct positioning between the filter system and the nozzle hereby supporting an efficient cleaning of the first filter.
Preferably, the filter system comprises a liquid guiding element adapted to cooperate with the nozzle of the filter wet cleaning unit. This cooperation is such that the liquid guiding element has a guiding or assisting function by guiding the liquid supplied from the nozzle of the filter wet cleaning unit towards the first filter. Thus the filter system enables the supplied liquid to be effectively distributed across the first filter's surface to be cleaned. Particularly, the liquid guiding element has simultaneously a functional property to constitute or provide the aforementioned filter alignment element.
According to further embodiments, the liquid guiding element is characterized by at least one of the following features:

having an elongated vane shape,
adapted to laterally expand the width of the nozzle such that the lateral width of a liquid curtain exiting the nozzle is expanded in lateral width,
having a liquid guiding surface that is inclined towards the surface of the first filter in a vertical downward direction,
a gap between the first surface of the first filter and the liquid guiding element, being part of the nozzle,
being arranged upstream the first filter with respect to the drying air flow.

Preferably, the liquid guiding element is adapted or designed such that the lateral expansion of the liquid curtain width is achieved as broad as the lateral width of the first filter. Such an expansion further supports uniform and effective liquid distribution over the first filter.
Preferably, the gap (respectively air gap) between the first filter and second filter has at least one of the following features:

the gap width is at least 1.5 mm, 2 mm, 4 mm or 5 mm,
the gap is wedge-shaped or approximately wedge-shaped.

Such a gap design provides a space-saving arrangement between the first and second filter in their operational position. At the same time, protecting the second filter from liquid cleaning the first filter is realized with low effort. Generally the 'gap width' relates to an average value of the width. The opposing surfaces of the filters between which the gap is formed may be parallel such that the width is constant. The opposing surfaces may be inclined to each other such that a wedge-like gap is formed. Or one or both surfaces may be curved.
In a further embodiment the first filter has a rear surface which is oriented in air flow direction towards the (front surface of the) second filter. In this regard, the air gap is dimensioned such that liquid flowing along the rear surface of the first filter is not contacting a front surface of the second filter. This dimension of the air gap is a further advantage measure for protecting the second filter against undesired wetting during cleaning the first filter. The rear surface of the second filter is particularly defined as a surface pointing to the exit direction of drying air flowed through the first filter. The front surface of the second filter is particularly defined as a surface facing the rear surface of the first filter and/or as a surface oriented towards the inflowing air to be filtered by the second filter. Preferably, the rear surface of the first filter faces the second filter, in particular the front surface of the second filter.
In a preferred embodiment the support structure is provided by a filter unit of the filter system. The filter unit preferably comprises a door or lid adapted to close an opening of the air channel of the apparatus.
By providing the filter unit and (where applicable) the door or lid, the removal of the filters from their operational position is simple and user-friendly. Further the door or lid is adapted to act as alignment element that (additionally) aligns the filters to the correct operational positions of the filters in the air channel. This ensures that the filters are placed in their correct operational position within the air channel thus preventing the drying air (which may contain impurities, lint, etc. from the drying process) to by-pass at least one of the filters and to enter into an undesired space, particularly inside the heat exchanger. Combining the door or lid with the filters offers a mechanical connection such that the whole filter system is insertable or extractable from the apparatus by only one simple user action.
In further embodiments the filter unit is adapted to be linearly or in a swinging or rotating movement inserted and extracted from the air channel. Thus the handling of the filter system is further simplified.
Preferably, the filter unit comprises a first filter frame for supporting the first filter and/or a second filter frame or chamber for supporting and receiving the second filter. This construction design facilitates removing or changing the filters separately or individually.
In another embodiment the first filter has at least one of the following features:

being a mesh-type filter,
being a woven filter,
being a flat or screen filter,
being formed of threads having a diameter in the range from 50 to 150 µm, from 70 to 160 µm, from 80 to 145 µm, or from 100 to 300 µm,
having a mesh opening width in the range of 50 to 175 µm, 80 to 200 µm, 100 to 250 µm, 120 to 185 µm, or 150 to 350 µm, and
having a thickness of or less than 1 mm, 0.8 mm, 0.5 mm or 0.3 mm.

Having at least one of the features, the first filter can be understood as a "coarse" filter in the meaning that it removes the main volume or load of the fluff, lint, etc. from the drying air.
Preferably, the second filter has at least one of the following features:

being a porous medium filter,
being a sponge- or foam-type filter,
being a non-woven filter
being made for a PU foam,
having a thickness in the range of 3 to 20 mm, 3 to 5 mm, 4 to 8 mm, 6 to 10 mm or 8 to 20 mm,
having a pore size in the range of 400 to 1.200 µm,
having a density in the range 5 to 60 kg/m³, 10 to 50 kg/m³, 20 to 30 kg/m³, 30 to 40 kg/m³ or 15 to 25 kg/m³, and
having a pore density per inch in the range of 10 to 60, 20 to 40, or 15 to 25 PPI.

Having at least one of the features, the second filter can be understood to be a "fine" filter in the meaning 'adapted to remove' the fine or small particles which passed the first filter or which were not caught by the first filter.
In further embodiments the first filter or the second filter or the first and second filters have hydrophobic surface properties or characteristics. Inexpensive bulk material can be provided to realize the filters. The bulk material may be any suitable hydrophobic material or may be provided with a surface finish or coating having hydrophobic properties. A first filter has hydrophobic properties adapted to prevent water sticking on the filter surface during cleaning. The hydrophobic property avoids or reduces the first filter becoming wet, which could hinder the drying air to pass freely the first filter and subsequently could reduce the dryer performance.
In preferred embodiments at least one of the following features is realized at the support structure of the filter system:

the first and second supporting positions in the support structure of the filter system are aligned such that when the first filter and the second filter are in their respective operational position, the first and second filters are oriented inclined to each other, and
the first supporting position is aligned such that, when the first filter is in its operational position, the first filter is inclined relative to the vertical axis.

Particularly, one or more surface planes of the first and second filters are inclined to each other. Thus a useful distance between the first and second filter can be designed (e.g. for realizing an air gap or for protecting the second filter from liquid during a first filter cleaning process).
In further embodiments the angle of inclination between the first and second filter or of the first filter relative to the vertical axis is equal to or greater than 2°, 3°, 5°, 10° or is in the range from 1° to 4°, 2° to 5° or 3° to 10°.
Preferably, the support structure of the filter system comprises one or more of the following features:

at least one latch or clip or at least one clamping arrangement for securing the first filter, the second filter or the first and second filter in the respective operational position within the filter system, and
at least one latch, clip or indentation for securing the filter system in or at the air channel of the laundry drying apparatus.

Thus low-cost parts provide a stable structure of the filter system and a stable position of the filter system relative to the air channel.
In a further preferred embodiment the first filter has a curvature. Particularly, a first surface of the first filter through which the drying air to be cleaned enters has a curvature. Such a curvature provides sufficient dispersion of the supplied cleaning liquid across the whole first filter surface to be cleaned. Additionally, the curvature is adapted to compensate potential production tolerances and subsequently potential misalignments between the filter wet cleaning unit (in particular its nozzle) and the first filter. When the filter system is in its operating position, the curvature extends preferably along a vertical section, wherein the plane of this section is perpendicular to the first surface of the first filter. Particularly, the first surface is opposite the surface of the first filter which is facing the second filter or is pointing towards the incoming drying air flow.
In a further embodiment the first filter has a first curvature and a second curvature, wherein the first curvature is in a vertical direction and the second curvature is in a horizontal direction. Additionally or alternatively, the surface of the first filter has a trough-like or valley-like shape adapted to horizontally concentrate a flow of liquid when the liquid is flowing from an upper region of the first filter to a lower region of the first filter. Thus the liquid flow across the first filter surface to be cleaned can be controlled for an efficient cleaning result.
Preferably, the first filter is supported by the support structure which comprises a frame or grill for imposing the curvature to the first filter. Thus an appropriate curvature is easily obtained if the first filter has flexible properties without the support structure, i.e. when the support structure is removed from the first filter.
According to a second aspect of the invention (the above is the 'first' aspect of the invention), a laundry drying apparatus (in particular a dryer or a washer-dryer) comprises a cabinet and a laundry storing compartment arranged within the cabinet. A laundry storing compartment and an air channel are arranged within the cabinet. The air channel is adapted to guide drying air from at least one air outlet of the laundry storing compartment. A filter system is arranged within the air channel downstream the laundry storing compartment. Preferably, the laundry drying apparatus comprises a heat exchanger arranged within the air channel and being adapted to cool the drying air, wherein the filter system is arranged upstream the heat exchanger. Further the laundry drying apparatus comprises a filter wet cleaning unit having a nozzle for supply liquid for cleaning or washing the filter system.
The nozzle is arranged to direct the liquid flowing out of the nozzle towards the front surface of the filter system.
The filter system comprises at least one filter alignment element adapted to cooperate with at least one counter-alignment element provided at the filter wet cleaning unit or at the air channel. Making a mechanical cooperation of the at least one filter alignment element and the at least one counter-alignment element the first filter is positionally aligned with the nozzle of the filter wet cleaning unit.
Additionally or alternatively, i.e. instead of the at least one filter alignment element, the filter system comprises a liquid guiding element adapted to cooperate with the nozzle of the filter wet cleaning unit such as to guide or assisting by guiding the liquid supplied from the nozzle of the filter wet cleaning unit towards the first filter.
The at least one filter alignment element is adapted to align accurately the filter system and subsequently the first filter relative to the nozzle when the filter system is inserted into the operational position within or at the air channel. The at least one filter alignment element may be arranged at the filter system in combination with the liquid guiding element. Alternatively or additionally, the liquid guiding element may have at the same time functional properties of being a filter alignment element.
Any feature of any laundry drying apparatus and/or filter system disclosed in the claims and/or the description and/or the figures may be applied to this laundry drying apparatus (having a filter alignment element or liquid guiding element) individually or in any arbitrary combination or sub-combination.
According to a third aspect of the invention, a filter system for a laundry drying apparatus (in particular a dryer or a washer-dryer) comprises a first lint filter (first filter) and a second lint filter (second filter). Further this filter system comprises a support structure having a first supporting position adapted to support the first filter and a second supporting position adapted to support the second filter. When the first and second filters are placed in the first and second supporting positions (first and second filter positions), respectively, the first and second filters are neighboring to each other or arranged adjacent to each other. The first filter is adapted to be washed or cleaned by liquid. When the first and second filters are placed in the first and second filter positions, an air gap is formed between the first filter and second filter.
Any feature of any filter system disclosed in the claims and/or the description and/or the figures may be applied to this latter filter system individually or in any arbitrary combination or sub-combination.
Individual features or sub-combinations of the first, second and/or third aspects of the invention can be mutually combined with any of the first, second or third aspect and any of the first, second or third aspects can be combined with individual features or sub-combinations of features of any of the below detailed embodiments.
Reference is made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying figures which show:

Fig. 1: a schematic view of a laundry treatment apparatus,
Fig. 2: a perspective view of a part of a filter system having a first filter and a second filter,
Fig. 3a: a front view of the filter system according to Fig. 2,
Fig. 3b: a side sectional view according to the section line III - III in Fig. 3a,
Fig. 4: a side sectional view of the filter system similar to Fig. 3b, but in-situ within a laundry treatment apparatus, showing the cooperation between the first filter and a nozzle,
Fig. 5: an enlarged side sectional view of the detail V in Fig. 9, showing aligned positioning between the first filter and the nozzle,
Fig. 6: a perspective front view of the filter system according to Fig. 9,
Fig. 7: a perspective rear view of the filter system according to Fig. 9,
Fig. 8: a front view of a basement of a laundry drying apparatus,
Fig. 9: a side sectional view of the basement according to the section line IX -IX in Fig. 8, showing a filter system in operational position within the laundry drying apparatus,
Fig. 10a: a perspective view of a laundry drying apparatus, showing a cabinet opening in an opened position hereby providing access to the inserted filter system,
Fig. 10b: the laundry drying apparatus according to Fig. 10a, showing the extraction of the filter system out of the apparatus in a first embodiment,
Fig. 10c: the laundry drying apparatus according to Fig. 10a, showing the extraction of the filter system out of the apparatus in a further embodiment,
Fig. 11: a perspective view of the filter system according to Fig. 10a - Fig. 10c,
Fig. 12: a top view of the filter system according to Fig. 11,
Fig. 13: a side sectional view of the filter system according to the section line XIII - XIII in Fig. 12,
Fig. 14: a perspective view of the filter system according to Fig. 11, showing the filter system in a detached state,
Fig. 15: a perspective view of the filter frame elements in a detached state,
Fig. 16: a perspective rear view of the filter frame elements according to Fig. 15,
Fig. 17: a perspective front view of a filter system in a further embodiment, and
Fig. 18: a perspective partial view of a laundry drying apparatus, showing the filter system according to Fig. 17 in an inserted position within the basement of the apparatus.

Fig. 1 shows schematically depicted a laundry drying apparatus 2 which in brief is denoted "apparatus" and is a heat pump tumble dryer in this embodiment. The tumble dryer 2 comprises a partly and schematically depicted cabinet 3 which supports or encloses components and parts exemplarily described hereinafter. The cabinet 3 encloses a heat pump system 4, including a closed refrigerant loop 6 which comprises in the following order of refrigerant flow B: a first heat exchanger 10 acting as evaporator for evaporating the refrigerant and cooling drying air, a compressor 14, a second heat exchanger 12 acting as condenser for cooling the refrigerant and heating the drying air, and an expansion device 16 from where the refrigerant is returned to the first heat exchanger 10. Together with the refrigerant pipes connecting the components of the heat pump system 4 in series, the heat pump system 4 forms the refrigerant loop 6 through which the refrigerant is circulated by the compressor 14 as indicated by arrow B.
The drying air flow A within the apparatus 2 is guided through a compartment 18 of the home appliance 2, i.e. through a compartment for receiving articles to be treated, e.g. a drum 18. The articles to be treated are laundry 19, textiles or the like. The drying air flow is indicated by arrows A in Fig. 1 and is driven by a drying air blower 8. A drying air channel 20 guides the drying air flow A outside the drum 18 and includes different sections, including the section forming a battery channel 20a in which the first and second heat exchangers 10, 12 are arranged. The drying air exiting the second heat exchanger 12 flows into a rear channel 20b in which the drying air blower 8 is arranged. The air conveyed by the blower 8 is guided upward in a rising channel 20c to the backside of the drum 18 which has one or more drum inlets 26for the drying air. The air is exiting the drum 18 through the drum outlet 28 (which corresponds to the loading opening 21 of the drum 18, wherein during drying operation the loading opening 21 is covered by a loading door 24) is optionally filtered by an optional fluff filter 22 arranged close to the drum outlet 28, e.g. in or at the channel 20. In the embodiment the optional fluff filter 22 is arranged in a front channel 20d forming another section of the channel 20 which is arranged behind and adjacent the front cover of the apparatus 2. The condensate formed at the first heat exchanger 10 is collected and guided to a condensate collector 30 which is connected to an extractable condensate drawer 40 via a drain pipe 46, a drain pump 36 and a drawer pipe 50. I.e. the collected condensate can be pumped from the collector 30 to the drawer 40 which is arranged at an upper portion of the apparatus 2 from where it can be comfortably withdrawn and emptied by a user.
As shown in Fig. 1, a filter system 52 is arranged in the cabinet 3 of the apparatus 2 to catch lint, fluff and other particles from the drying air before this drying air enters the first heat exchanger 10. The filter system 52 is arranged within the air channel 20 downstream the drum 18 and upstream the first heat exchanger 10. Particularly, the filter system 52 is arranged in the basement 5 which is arranged at a bottom region of the apparatus 2.
Fig. 2 shows some elements of the filter system 52. It comprises a first lint filter 54 and a second lint filter 56. The filter system 52 comprises a support structure 58 for supporting the filters 52, 54. The support structure 58 comprises a rectangular first filter frame 60 having a first supporting position for supporting the first filter 54. The support structure 58 further comprises a rectangular second filter frame 62 having a second supporting position adapted to support the second filter 56.
Regarding both filters 54, 56, the drying air flow A first enters a front surface 64 of the first filter 54 whereas a rear surface 66 of the first filter 54 is directed towards or is facing the second filter 56 (Fig. 3a, Fig. 3b). Fig. 3b shows the first and second filters 54, 56 placed in their first supporting position and second supporting position, respectively, wherein the positions are such that an air gap 68 is formed between the first filter 54 and second filter 56. In the embodiment the air gap 68 is approximately wedge-shaped. The width of the air gap 68 along the lateral direction 96 is dimensioned preferably at least 1.5 mm, 2 mm, 4 mm or 5 mm. in the embodiment shown the width is a maximum width of the wedge-shaped gap at the lower end. In embodiments the gap width between the filters may be constant or variable within e.g. less than 80%, 60% or 30% variation from a mean gap width.
The first filter frame 60 is carrying a grill 63 or grid which is adapted to keep the first filter 54 in a desired surface form, e.g. a flat plane in this embodiment. According to Fig. 2 and Fig. 3b, the surface plane is spanned by a horizontal direction 75 and a surface direction 77.
Fig. 3b and Fig. 4 show that the first and second supporting positions of the first and second filters 54, 56 are aligned such that when the first and second filters 54, 56 are in their respective operational positions, the first filter 54 and the second filter 56 are oriented inclined to each other. Additionally, the first filter 54 is inclined relative to a vertical axis 110 of the support structure 58 extending in parallel to the vertical direction 76 or in parallel to a vertical plane of the support structure 58. The angle 112 of inclination between the first filter 54 and second filter 56 and of the first filter 54 relative to the vertical axis 110 is preferably equal to or greater than 2°, 3°, 5°, 10° or is preferably in the range from 1° to 4°, 2° to 5° or 3° to 10°.
In order to provide an automatic washing/cleaning of the first filter 54, the apparatus 2 comprises a filter wet cleaning unit 70 as shown in Fig. 4. This wet cleaning unit 70 has a nozzle 72 for supplying liquid for washing the first filter 54. The nozzle 72 is arranged to direct the liquid flowing out of the nozzle 72 towards the front surface 64 of the first filter 54. In this regard, the first filter 54 is configured and arranged relative to the nozzle 72 to (at least substantially) screen or protect the second filter 56 from undesired contact with liquid flowing out of the nozzle 72. Preferably, the nozzle 72 is dimensioned and adapted to distribute the liquid over or essentially over the full horizontal width 74 of the front surface 64 of the first filter 54 (Fig. 3a). The horizontal width 74 extends parallel to a horizontal direction 75, whereas the horizontal direction 75 extends perpendicular to the vertical direction 76. A surface direction 77 of the first filter 54 is inclined relative to the vertical direction 76. The horizontal direction 75 and the surface direction 77 span the surface plane of the first filter 54, particularly its front surface 64.
It is noted that using the terms "horizontal" and "vertical" is not intended as limiting in orientation. Rather, using these terms is to indicate that the two directions are orthogonal or perpendicular to one another, or that "horizontal" is orthogonal/perpendicular to the vertical direction, regardless of whether the vertical direction is aligned with the direction of gravity or not. In a preferred embodiment the vertical direction used herein is in fact aligned with the direction of gravity. The directions relate to the intended ('upright') operational position of the dryer 2.
According to Fig. 4 and Fig. 5, the nozzle 72 is arranged at or within the air channel 20 relative to the first filter 54 such as to supply the liquid to an upper region 80 and preferably to the top front edge of the first filter 54. In Fig. 4 and Fig. 5 one nozzle outlet 78 is shown. However, the nozzle 72 may have two, three or more nozzle outlets 78 which are preferably arranged distributed and spaced along the horizontal direction 75. The at least one nozzle outlet 78 is adapted to direct the liquid towards the first filter 54. Preferably, the at least one nozzle outlet 78 is an elongated outlet having an elongated extension along the horizontal direction 75 and particularly in parallel to the front surface 64 of the first filter 54.
The liquid is flowing out of the nozzle 72 along a flow direction 82 which is particularly in parallel to the vertical direction 76 (Fig. 4). The front surface 64 of the first filter 54 extends in surface direction 77. Thus the flow direction 82 and the surface direction 82 are inclined to each other by an inclination angle 84. Further in the embodiment according to Fig. 4, the nozzle 72 is oriented relative to the front surface 64 of the first filter 54 such that the liquid flowing out of the nozzle 72 hits the front surface 64 of the first filter 54 approximately under the inclination angle 84. In Fig. 4, the inclination angle is about 3°. In contrast to Fig. 4, the liquid flowing out of the nozzle 72 according to the embodiment in Fig. 5 hits the front surface 64 of the first filter 54 under a greater inclination angle 85 than the inclination angle 84 due to a liquid guiding element 86 to be explained in more detail below.
As can be seen in Fig. 4, the filter system 52 and the filters 54, 56 are placed in their respective operational positions within the apparatus (not shown in detail here). In this regard, the nozzle 72 of the filter wet cleaning unit 70, the first filter 54 and the second filter 56 are arranged such that the first filter 54, in particular its front surface 64, forms a screen adapted to prevent liquid flowing out of the nozzle 72 to reach onto the surface of the second filter 56. Preferably, the air gap 68 is dimensioned such that liquid flowing along the rear surface 66 of the first filter 54 is not contacting a front surface 57 of the second filter 56 (Fig. 3b, Fig. 4).
Fig. 5 shows in cross section a wedge-like filter alignment element 88 being part of the filter system 52. This element 88 interacts with a nozzle wall section 90 in the region of its nozzle outlet 78. The wall section 90 is acting as a counter-alignment and/or abutting element. The mechanical cooperation of the wall section 90 and the filter alignment element 88 enables the first filter 54 to be positionally aligned with the nozzle 72. In other words, the filter system 52 and subsequently the first filter 54 to be cleaned is accurately positioned with respect to the nozzle outlet 78 by effecting a positioning mechanical contact between the filter alignment element 88 and the counter-alignment element 90. In other preferred embodiments the counter-alignment element 90 is replaced or supplemented by parts of the wet cleaning unit 70 or the drying air channel 20, e.g. like one or more rest or stopping elements.
The embodiment of the filter alignment element 88 according to Fig. 5 is acting at the same time as a liquid guiding element 86 (mentioned above). This element 86 is adapted to cooperate with the nozzle 72 such that the element 86 has a guiding or assisting function by guiding the liquid supplied from the nozzle outlet 78 towards the first filter 54. In other embodiments the filter system 52 comprises at least one filter alignment element 88 and a separate liquid guiding element 86.
The design or shape of the liquid guiding element 86 is adapted to achieve an efficient distribution of the liquid across the front surface 64 to clean the first filter 54 from top to bottom. Preferably, the liquid guiding element has an elongated vane shape (Fig. 6, Fig. 7). Particularly, the liquid guiding element 86 is adapted to laterally expand the width of the nozzle 72 such that the lateral width (which extends along a lateral direction 96) of a liquid curtain exiting the nozzle outlet 78 is expanded in lateral width thus enabling a uniform cleaning of the first filter 54, preferably along its complete lateral width along the lateral direction 96.
Further the liquid guiding element 86 has a liquid guiding surface 92 which is inclined relative to the flow direction 82 or vertical direction 76 (Fig. 5, Fig. 6, Fig. 7). Thus the liquid guiding element 86 is inclined towards the front surface 64 of the first filter 54 in a vertical downward direction. When the filter system 52 is in its operational position according to Fig. 5, a gap 94 is achieved between the front surface 64 of the first filter 54 and the liquid guiding element 86. This gap 94 can be regarded as an extension of the nozzle 72 or its nozzle outlet 78. The gap 94 and the liquid guiding element 86 are arranged upstream the first filter 54 with respect to the drying air flow A.
Fig. 6 and Fig. 7 show the liquid guiding element 86 and the filter alignment element 88 (already known from Fig. 5) in a perspective view. This element 86, 88 is arranged at the support structure 58, wherein in Fig. 6 and Fig. 7 only the first filter 54 is shown.
The first filter 54 is preferably a thin (e.g. thickness of or less than 1 mm, 0.8 mm, 0.5 mm or 0.3 mm) mesh-type filter whereas the second filter 56 is substantially thicker (e.g. thickness in the range of 3 to 20 mm, 3 to 5 mm, 4 to 8 mm, 6 to 10 mm or 8 to 20 mm) than the first filter 54. Preferably, the second filter 56 is a non-woven type filter (e.g. foam material, PU foam).
The wet cleaning unit 70 may be controlled by a controller of the dryer (not shown) such that the first filter 54 is automatically washed/cleaned at a defined time and/or predefined periods, preferably and/or after every drying cycle.
The second filter 56 is not washed by the wet cleaning unit 70 but its material and form structure is adapted to collect fine particles by the second filter 56 for long periods of dryer operation time, i.e. over many drying cycles, before it is necessary to replace/change or clean the second filter 56 by the user.
This concept of a filter system 52 relieves the user from the burden to clean lint filters after every drying cycle and at the same time offers a constant drying performance, energy consumption and cycle duration, primarily by preventing a degradation of the heat exchange efficiency of the first heat exchanger by preventing fluff deposition.
Fig. 8 shows the bottom region of the apparatus 2 having the basement 5 where the filter system 52 is inserted in its operational position. In general, the air channel 20 comprises a channel opening 98 which can be closed by inserting the filter system 52 in its operational position (Fig. 1, Fig. 8, Fig. 9). In more detail, the support structure 58 has a filter unit 59 which comprises a door 100 or lid adapted to close the channel opening 98.
Fig. 10a shows the apparatus 2 with the filter system 52 inserted in its operational position. The door 100 of the filter system 52 is arranged adjacent to a cabinet opening 102 (air channel opening). The door 100 and the cabinet opening 102 are covered by a pivotable cabinet door 104 shown in Fig. 10a in the opened position.
Fig. 10b shows the filter unit 59 according to Fig. 10a but being in a partially extracted position relative to the air channel 20. Thus the air channel 20 is opened at the channel opening 98. The filter unit 59 can be extracted and again be inserted by a swing-like movement or a rotational movement.
Fig. 10c shows a further embodiment, according to which the filter unit 59 is extracted from the air channel 20 by making a linear movement. Insertion of this filter unit 59 into the channel opening 98 is again made by a linear movement.
The door 100 being part of the filter unit 59 (more generally of the support structure 58) provides a user-friendly handling of the filter system 52. The filter system 52 is insertable into the air channel 20 and extractable therefrom by simply handling it at the door 100. The door 100 comprises a latch 106 which is pivotably mounted at the door and movable by a handle 108 (Fig. 11, Fig. 13, Fig. 14). When the support structure 58/filter unit 59 is inserted into the channel opening 98 the latch 106 will be rotated into a respective position relative to the cabinet 3 thus securing the filter system 52 in or at the air channel 20.
Fig. 11 shows the support structure 58 carrying two sealing elements 114. When the filter system 52 is in its operational position at or in the air channel 20, these sealing elements 114 are adapted to provide the tightness of the channel opening 98 and other parts of the apparatus 2. The front seal 114 seals between door 100 and basement and thus the channel 20 from the ambient air of the dryer. The rear seal prevents lint from bypassing the filters within the air channel 20.
Fig. 12 shows that the bottom region of the support structure 58 comprises an elongated, approximately rectangular hole 116. This hole 116 provides a passage for the supplied liquid to drop or flow down into a liquid chamber of the basement 5 below the filter structure 58.
Fig. 13 shows a deflecting wall 118 being part of the support structure 58. The curved surface of the wall 118 supports guiding the drying air towards the first heat exchanger 10 and thereby reducing the flow resistance. Additionally the wall 118 guides the supplied liquid towards the hole 116 for draining the liquid out of channel 20.
Fig. 14 to Fig. 16 show clamping arrangements for securing the first filter 54 and the second filter 56 in the respective operational position at the support structure 58 and within the filter system 52. A first clamping arrangement comprises two parallel side elements 120 which are mounted at a rear side of the door 100 (Fig. 14). Each of the rear edges of the side elements 120 cooperate and/or mate with a respective slot-like recess 122. The recesses 122 are arranged at the first filter frame 60. Thus the door 100 can be secured relative to the first and second filters 54, 56 by coupling the rear edges of the side elements with the recesses of the filter frame.
An additional clamping arrangement is provided to secure the first filter 54 and second filter 56 with each other (Fig. 15, Fig. 16). For this purpose, the first filter frame 60 comprises one or more snap-in elements 124 (e.g. detents, studs, bolts, recesses) mating or cooperating with respective one or more counter-elements (e.g. at least one groove, recess or hole, pins, bolts) arranged at the second filter frame 62 (not shown in detail). Thus both frames 60, 62 and subsequently both filters 54, 56 are secured in their operational position. Additionally, both filters 54, 56 could be separated easily from each other (e.g. for replacing one of the filters 54, 56 or for cleaning the second filter 56) by detaching the snap-in elements 124 from the counter-elements. Alternatively or additionally, the clamping functions explained according to Fig. 14 to Fig. 16 may be implemented by at least one latch or clip or any other appropriate element.
Fig. 17 shows a further embodiment of the first filter 54. The front surface 64 and consequently the first filter 54 have a curvature 126. The cross section of the curvature 126 extends particularly along the vertical direction 76. Additionally or alternatively, the first filter 54 may have a first curvature and a second curvature, wherein the first curvature extends along the vertical direction 76 and the second curvature extends along the horizontal direction 75. Further the first filter 54 may have a trough-like or valley-like shape or curvature. This trough-like or valley-like shape is preferably adapted to horizontally concentrate a flow of liquid when the liquid is flowing from an upper region 80 of the first filter 54 to a lower region 81 of this filter 54.
According to Fig. 17, the first filter 54 is supported by the support structure 58 comprising a curved first filter frame 60 and a grill 63 comprising curved ribs 128. The curved frame 60 and the curved ribs 128 impose the curvature 126 to the first filter 54. This may be easily realized when the first filter 54 has flexible properties. Even if not shown in detail, the support structure 58 according to Fig. 17 is adapted to support also the second filter 56.

Fig. 18 shows the embodiment of the filter system 52 according to Fig. 17 being in its operational position, i.e. in its inserted position within the basement 5 of the apparatus 2. By user handling the filter system 52 is manually extractable out of the basement 5 and can be inserted back therein.

Reference Numeral List:

2	tumble dryer	22	filter element
3	cabinet	24	loading door
4	heat pump system	26	drum inlet
5	basement	28	drum outlet
6	refrigerant loop	30	condensate collector
8	blower	36	drain pump
10	first heat exchanger	40	condensate container
12	second heat exchanger	46	drain pipe
14	compressor	50	drawer pipe
16	expansion device	52	filter system
18	drum	54	first lint filter
19	laundry	56	second lint filter
20	drying air channel	57	front surface of second filter
20a	battery channel		58	support structure
20b	rear channel	59	filter unit
20c	rising channel		60	first filter frame
20d	front channel		62	second filter frame
21	loading opening	63	grill
64	front surface of first filter	96	lateral direction
66	rear surface of first filter	98	channel opening
68	air gap	100	door
70	filter wet cleaning unit	102	cabinet opening
72	nozzle	104	cabinet door
74	horizontal width	106	latch
75	horizontal direction	108	handle
76	vertical direction	110	vertical axis
77	surface direction	112	angle of filter inclination
78	nozzle outlet	114	sealing element
80	upper region of first filter	116	hole
81	lower region of first filter	118	deflecting wall
82	flow direction	120	side element
84	inclination angle	122	recess
85	greater inclination angle	124	snap-in element
86	liquid guiding element	126	curvature
88	filter alignment element	128	curved rib
90	nozzle wall section	A	drying air flow
92	liquid guiding surface	B	refrigerant flow
94	gap

Claims

Laundry drying apparatus, in particular dryer (2) or washer-dryer, comprising:
a cabinet (3),

a laundry storing compartment (18) arranged within the cabinet (3),

an air channel (20) arranged within the cabinet (3) and adapted to guide drying air in a drying air flow (A) from at least one air outlet (28) of the laundry storing compartment (18) to at least one air inlet (26) of the laundry storing compartment (18),

a heat exchanger (10) arranged within the air channel (20) and being adapted to cool the drying air,

a filter system (52) arranged within the air channel (20) downstream the laundry storing compartment (18) and upstream of the heat exchanger (10), wherein the filter system (52) comprises a first lint filter (54), and

a filter wet cleaning unit (70) having a nozzle (72) for supply liquid for washing the first filter (54),

wherein the nozzle (72) is arranged to direct the liquid flowing out of the nozzle (72) towards a front surface (64) of the first filter (54);

characterized in that

the filter system (52) further comprises a second lint filter (56), wherein, when the filter system (52) is arranged within the air channel (20), the first lint filter (54) is arranged upstream the second lint filter (56), and

the first filter (54) is configured and arranged relative to the nozzle (72) to screen or to substantially screen the second filter (56) from contact with liquid flowing out of the nozzle (72), such that no or essentially no liquid supplied to the first filter (54) can contact the front surface of the second filter (56).
Laundry drying apparatus according to claim 1, wherein the filter system (52) comprises a support structure (58, 59) having a first supporting position adapted to support the first filter (54) and a second supporting position adapted to support the second filter (56), wherein, when the first and second filters (54, 56) are placed in the first and second positions, an air gap (68) is formed between the first (54) and second filter (56).
Laundry drying apparatus according to any of the previous claims, wherein the nozzle (72) is characterized by one or more of the following:
the nozzle is adapted to distribute the liquid over or essentially over the horizontal width (74) of the front surface (64) of the first filter (54),

the nozzle is arranged at or within the air channel (20) relative to the first filter (54) such as to supply the liquid to an upper region (80) of the first filter (54),

the nozzle has one, two, three or more outlets (78) adapted to direct the liquid towards the first filter (54), and

the nozzle has at least one elongated outlet (78) having the elongated extension in parallel to the first filter surface (64).
Laundry drying apparatus according to any of the previous claims, wherein the air channel (20) comprises a channel opening (98) and the first and second filters (54, 56) are designed such as to be removable from the air channel (20) through the channel opening (98).
Laundry drying apparatus according to any of the previous claims,
wherein the liquid flowing out of the nozzle (72) of the filter wet cleaning unit (70) has a first direction (82) and the surface plane of the first filter (54) has a second direction (77), wherein the first and second directions (77, 82) are inclined to each other by an inclination angle (84), or
wherein the nozzle (72) is oriented relative to the surface (64) of the first filter (54) such that the liquid flowing out of the nozzle (72) hits the surface (64) of the first filter (54) under an inclination angle (85),
wherein the inclination angle (84, 85) is preferably at or more than 2°, 3°, 5°, 10° or in the range from 1° to 4°, 2° to 5° or 3° to 10°.
Laundry drying apparatus according to any of the previous claims, wherein, when the filter system (52) and the first and second filters (54, 56) are placed in their respective operational positions in the laundry drying apparatus (2), the nozzle (72) of the filter wet cleaning unit (70), the first filter (54) and the second filter (56) are arranged such that the first filter (54) forms a screen adapted to prevent liquid flowing out of the nozzle (72) to reach onto the surface (57) of the second filter (56).
Laundry drying apparatus according to any of the previous claims, further comprising a heat pump system (4) comprising the heat exchanger as first heat exchanger (10) and a second heat exchanger (12) for heating the drying air.
Laundry drying apparatus according to any of the previous claims, wherein the filter system (52) comprises at least one filter alignment element (88) adapted to cooperate with at least one counter-alignment element (90) provided at the filter wet cleaning unit (70, 72) or at the air channel (20), wherein by the mechanical cooperation of the at least one filter alignment element (88) and the at least one counter-alignment element (90) the first filter (54) is positionally aligned with or positionally adjusted relative to the nozzle (72) of the wet cleaning unit (70).
Laundry drying apparatus according to any of the previous claims, wherein the filter system (52) comprises a liquid guiding element (86) adapted to cooperate with the nozzle (72) of the wet cleaning unit (70) and is adapted to guide or to assist in guiding the liquid supplied from the nozzle (72) of the wet cleaning unit (70) towards the first filter (54).
Laundry drying apparatus according to claim 9, wherein the liquid guiding element (86) is characterized by one or more of:
having an elongated vane shape,

adapted to laterally expand the width of the nozzle (72) such that the lateral width of a liquid curtain exiting the nozzle (72) is expanded in lateral width (96),

having a liquid guiding surface (92) that is inclined towards the surface (64) of the first filter (54) in a vertical downward direction (76),

the liquid guiding element (86) is arranged with respect to the first filter (54) such that there is a gap (94) between the first surface (64) of the first filter (54) and the liquid guiding element (86),

being part of the nozzle (72), and

being arranged upstream the first filter (54) with respect to the drying air flow (A).
Laundry drying apparatus according to any of the previous claims and claim 2, wherein the air gap (68) or the average value of the air gap or the minimum air gap between the first (54) and second filter (56) is characterized by one or more of the following:
the gap width is at least 1.5 mm, 2 mm, 4 mm or 5 mm, and

the air gap (68) is wedge-shaped.
Laundry drying apparatus according to any of the previous claims, wherein the first filter (54) has a rear surface (66) which, with respect to the drying air flow (A), is oriented towards the front surface of the second filter (56) and wherein a or the air gap (68) between the filters is dimensioned such that liquid flowing along the rear surface (66) of the first filter (54) is not contacting front surface (57) of second filter (56).
Laundry drying apparatus according to claim 2 or any of the previous claims 3 to 12 when also depending on claim 2, wherein the support structure (58) is provided by a filter unit (59) of the filter system (52).
Laundry drying apparatus according to claim 13, wherein the filter unit (59) comprises a door (100) or lid adapted to close an opening (98) of the air channel (20) of the laundry drying apparatus (2).
Laundry drying apparatus according to claim 13 or 14, wherein the filter unit (59) is adapted to be linearly or in a swing-movement inserted and extracted from the air channel (20).
Laundry drying apparatus according to any of the claims 13 to 15, wherein the filter unit (59) comprises one or both of
- a first filter frame (60) for supporting the first filter (54), and

- a second filter frame (62) or receptacle or chamber for supporting and receiving the second filter (56).
Laundry drying apparatus according to any of the previous claims, wherein the first filter (54) is characterized by one or more of:
being a mesh-type filter,

being a woven filter,

being a flat or screen filter,

being formed of threads having a diameter in the range from 50 to 150 µm, from 70 to 160 µm, from 80 to 145 µm, or from 100 to 300 µm,

having a mesh opening width in the range of 50 to 175 µm, 80 to 200 µm, 100 to 250 µm, 120 to 185 µm, or 150 to 350 µm, and

having a thickness of or less than 1, 0.8, 0.5 or 0.3 mm.
Laundry drying apparatus according to any of the previous claims, wherein the second filter (56) is characterized by one or more of:
being a porous medium filter,

being a sponge- or foam-type filter,

being a non-woven filter

being made of a PU foam,

having a thickness in the range of 3 to 20 mm, 3 to 5 mm, 4 to 8 mm, 6 to 10 mm or 8 to 20 mm,

having a pore size in the range of 400 to 1.200 µm,

having a density in the range 5 to 60 kg/m³, 10 to 50 kg/m³, 20 to 30 kg/m³, 30 to 40 kg/m³ or 15 to 25 kg/m³, and

having a pore density per inch in the range of 10 to 60, 20 to 40, or 15 to 25 PPI.
Laundry drying apparatus according to any of the previous claims, wherein the first filter (54), the second filter (56) or the first and second filters (54, 56) have a hydrophobic surface characteristics.
Laundry drying apparatus according to claim 2 or any of the previous claims 3 to 19 when also depending on claim 2,
wherein in the support structure (58) of the filter system (52) the first and second supporting positions are aligned such that when the first filter (54) and the second filter (56) are in their respective operational position, the first and second filters (54, 56) are oriented inclined to each other, or
wherein in the support structure (58) of the filter system (52) the first supporting position is aligned such that, when the first filter (54) is in its operational position, the first filter (54) is inclined relative to the vertical axis (110), where the vertical axis (110) is aligned with the direction of gravity.
Laundry drying apparatus according to claim 20, wherein an angle of inclination (112) between the first (54) and second filter (56) or of the first filter (54) relative to the vertical axis (110) is equal to or greater than 2°, 3°, 5°, 10° or is in the range from 1° to 4°, 2° to 5° or 3° to 10°.
Laundry drying apparatus according to claim 2 or any of the previous claims 3 to 21 when also depending on claim 2, wherein the support structure (58) of the filter system (52) comprises one or more of:
at least one latch or clip or at least one clamping arrangement (120, 122; 124) for securing the first filter (54), the second filter (56) or the first (54) and second filter (56) in the respective operational position within the filter system (52), and

at least one latch (106), clip or indentation for securing the filter system (52) in or at the air channel (20) of the laundry drying apparatus (2).
Laundry drying apparatus according to any of the previous claims, wherein
(a) the first filter (54) has a curvature (126) or wherein the front surface (64) of the first filter (54) through which the drying air to be cleaned enters has a curvature (126), or

(b) the first filter (54) has a first and a second curvature, wherein the first curvature (126) is in a vertical direction (76) and the second curvature is in a horizontal direction (75).
Laundry drying apparatus according to option (a) of claim 23, wherein the front surface (64) of the first filter (54) has a trough or valley shape adapted to horizontally concentrate a flow of liquid when the liquid is flowing from an upper region (80) of the first filter (54) to a lower region (81) of the filter (54).
Laundry drying apparatus according to claim 23 or 24 when also depending on claim 2, wherein the first filter (54) is supported by the support structure (58) comprising a frame or grill (63, 128) imposing the curvature (126) to the first filter (54).