The invention relates to a heat pump for a household appliance, in particular a laundry treatment appliance, comprising a compressor, a condenser, a restrictor, and an evapora- tor. The invention further relates to a household appliance, in particular a laundry treatment appliance, comprising such heat pump.

A laundry dryer having a heat pump as specified typically comprises a refrigerant circuit and an air path. The refrigerant circuit comprises the compressor, the condenser, the restrictor and the evaporator which are connected in series by refrigerant lines. The refrigerant flows through the compressor, the condenser, the restrictor and the evaporator, in this order, and through the lines connecting these to one another. The refrigerant releases heat to the process air as flowing through the air path by means of the condenser and extracts heat and humidity from the process air flowing through the air path by means of the evaporator. The compressor converts mechanical power to thermal power by compressing the refrigerant in the refrigerant circuit.

Within the air path or process air circuit, process air flows from a drum to the evaporator. At a drum outlet, the air is at a medium temperature and relatively wet. At the evaporator, the air is cooled and dehumidified and then flows to the condenser where it is heated. Hot and dry air is then introduced again into the drum where it absorbs moisture from laundry contained in the drum. The evaporator and the condenser are thus acting as heat exchangers having a refrigerant side and a process air side. The use of a heat pump in a laundry dryer and its general layout are well-known in the art, as shown in prior art docu- ments EP 1 632 736 A2, EP 1 593 770 B1 , WO 2013/060626 A1 , WO 2013/023958 A1 , WO 2012/065916 A1 , WO 201 1/080045 A1 , US 2010/0154248 A1 , and

US 2011/0209484 A1.

The evaporator and the condenser may be of a tube-and-fins type. The tubes of the evaporator and the condenser may be separate entities as described in prior art documents WO 2008/004802 A3, EP 2 261 416 A1 , EP 2 244 044 A2, EP 2 644 768 A1 , EP 2 418 448 A1 , WO 2013/153972 A1 , EP 2 468 948 A2, and EP 1 593 770 B1 , or may be joined in a common core, as described in prior art document WO 2008/004802 A3. In frontal view parallel to the length of the tubes the tubes may be arranged in columns (or rows) each comprising several tubes. A distance between neighboring columns is called a 'longitudinal spacing', and a distance between neighboring tubes of one column is called a 'transversal spacing'.

Another typical construction of the evaporator and the condenser is the so-called aluminium single-tube type (no-frost type) in which an aluminium tube is bent and fins are placed along it without tube expansion. An outer diameter of the tubes of the evaporator and the condenser used at present in a heat pump dryer are as follows: 3/8" (9.525 mm) and 7 mm for tube-and-fins type evaporators and condensers and 8 mm for aluminium single-tube type evaporator and condenser. A laundry dryer comprising a heat pump has an improved efficiency (in terms of kWh/kg) as compared to a conventional laundry dryer only employing an electrical heater. Thus, in principle a related operational carbon dioxide emission of the laundry dryer comprising the heat pump is lower than that of a conventional dryer due to its lower electric consumption. However, a refrigerant used in the heat pump must be taken into account with its GWP ('Global Warming Potential') which contributes to a total TEWI (Total Equivalent Warming Impact') by direct or indirect emission of the refrigerant into the atmosphere. Nowadays, typical refrigerants used in a heat pump are fluorinated hydrocarbon compounds (HFC) whose GWP maybe as high as 1500, or even higher. One possibility to reduce TEWI of these systems is to use hydrocarbon refrigerants that have low GWP like R-290 (propane) or R-1270 (propylene). The main drawback of these refrigerants is that they are flammable and therefore IEC 60335-2-1 1 standard limits the maximum charge to 150 g of refrigerant in a laundry dryer. It is generally known that an optimum refrigerant charge can be found for a specific system, but the refrigerant limit of 150 g imposed by the IEC 60335-2-1 1 standard is typically lower than the optimum charge of refrigerant for a heat pump of a typical laundry dryer. Efficiency is also affected by the compressor. For example, the efficiency of a rotary compressor is affected by different geometries of its components, including discharge and suction ports and rotor and cylinder geometries. The variation of these geometries implies differences in mechanical frictions and in the thermodynamic behaviour of the refrigerant inside the compressor. In more detail, the losses in the compressor that determine its efficiency include the following: energy losses stemming from motor losses, friction losses, compression losses due to not ideal compression, valve losses due to gas pulsations and over-compression, and lubricant pumping losses, as well as mass flow losses stemming from clearance volume losses due to valve and cylinder head dimensions, leakage losses, back-flow-losses, suction gas heating losses due to a gas density at a cylinder inlet, and losses due to lubricant flow.

It is an object of the current invention to at least partially overcome at least some of the problems of the art with respect to heat pumps for household appliances, in particular laundry treatment appliances, and to particularly provide a heat pump for a household appliance, in particular laundry treatment appliance, which has a reduced GWP and an improved efficiency.

The object is achieved by the features of the independent claims. Preferred embodiments are particularly referred to in the dependent claims, in the subsequent decription and in the attached drawing.

Accordingly, the object is achieved by a heat pump for a household appliance, in particular a laundry treatment appliance, comprising a compressor, a condenser, a restrictor, and an evaporator, that are connected in series by a refrigerant loop containing flammable refrigerant, wherein the condenser ('condenser coil') is of a tube-and-fin type with the tubes having an outer diameter of less than 7 mm.

This leads to a higher heat transfer from a refrigerant side to an air side by means of: reducing a system volume for the refrigerant, increasing a convection coefficient at the refrigerant side, creating a good balance between pressure losses and a size of a second ary surface at the air side, allowing a cooling down of the refrigerant even at low charge (i.e. a higher subcooling), and reaching a proper condensation pressure. This can even be achieved by having a quantity of flammable refrigerant of 150 grams or less within the heat pump.

The laundry treatment appliance may in particular be a laundry dryer. The household appliance may also be a washing machine, a dishwasher, a cooling apparatus etc.

The condenser and the evaporator are typically arranged as heat exchangers, in particular refrigerant/air heat exchangers that are passed by process air of the household appliance.

It is a preferred variant or embodiment that the evaporator ('evaporator coil') is of a tube- and-fin type with the tubes having an outer diameter of 7 mm or less. It is another preferred variant that an outer diameter of the tubes of the condenser ("condenser coil") is about 6 mm or less, in particular 5,5 mm or less, in particular 5 mm or less.

It is another preferred embodiment that a transversal spacing of the tubes of the conden- ser is 21 mm or less while a longitudinal spacing is 19 mm or less. This leads to a higher heat transfer from a refrigerant side to an air side by means of: increasing a convection coefficient at the air side, creating a good balance between pressure losses and a size of a secondary surface at the air side, allowing a cooling down of the refrigerant even at low charge (i.e. a higher subcooling), and reaching a proper condensation pressure. It may be preferred that this is also holds for the evaporator coil and its tubes.

To improve efficiency of the compressor, in particular a rotary compressor, it is preferred that a roller of the compressor has a height-to-radius ratio of 1.4 to 1.2, in particular smaller than 1.4. The roller may in particular be shaped as a hollow cylinder with the height measured along its longitudinal axis. The radius is typically measured perpendicular from the longitudinal axis to an outer diameter of the cylinder. This embodiment reduces friction losses and therefore increases the efficiency of the compressor by achiev ing the same cooling capacity with a lower power input. A height-to-radius ratio of current rollers of rotary compressors used laundry dryers is between 1.7 and 1.5. It is a particular variant of the compressor according to the invention that the height-to-radius ratio is between 1.4 and 1.2.

It is another preferred embodiment that an area of a discharge port of the compressor, in particular rotary compressor, is 19.8 mm ² (square millimeters) or higher. This also achieves an increased efficiency of the compressor (same cooling capacity with a lower power input) and by reducing a pressure drop in a discharge valve.

It is even another preferred embodiment that a displacement of the compressor is between 6 cc (cubic centimeters) and 9.5 cc. If the compressor displacement is bigger than 9.5 cc it might be required to increase a heating capacity at the condenser in order to enable proper dissipation of energy pumped from compressor. This would mean a higher condenser area and volume. This in turn, would require an increase in refrigerant charge in order to allow the condensation of the refrigerant in the condenser which is not desired due to the dryer safety standard limitation of 150 g for flammable refrigerants. If the compressor displacement is lower than 6 cc then the refrigerant mass flow rate will decrease so much that an energy transfer in the heat exchangers is negatively affected.

It is another preferred embodiment that an oil quantity within the compressor is between 150 cc and 210 cc for improved performance. Particularly preferred is an oil quantity equal or less than 180 cc. It is preferred that the oil in the compressor has a reduced solubility with the refrigerant. Particularly, solubility is lower than 35%. This in particular holds at a working point of the heat pump dryer at a pressure of about 26 bar (e.g. 26 +/- 0.5 bar) with a condensation pressure at 70°C) and a mix temperature of the oil and e.g. R290 of 80°C. A proper combination of oil type and quantity of it increases the amount of available refrigerant in the heat exchangers and assures a good lubrication and internal leakage sealing at the compressor providing good volumetric efficiency. This embodiment makes use of the fact that the main amount of the refrigerant of the heat pump is located in the condenser coil (because of a high inner volume of its coil and a relatively high density of the refrigerant) and in the compressor (where the refrigerant is mixed with oil). The refrigerant inside the compressor that is mixed with oil is not available in the heat exchangers for energy transfer purpose. Therefore, the higher the amount of refrigerant mixed with oil inside the compressor, the less amount of refrigerant is available in the heat exchangers to reach the optimum working point (in particular under the regime of the 150g limitation of flamma- ble refrigerants according to dryer standard IEC 60335-2-11). In other words, the less refrigerant is mixed with oil inside the compressor the higher is the amount of refrigerant within the heat exchangers. This in turn leads to the effects that subcooling is increased to maintaining constant the superheating, that the dehumidification rate is increased (due to a higher difference of enthalpy in the evaporator) and that a reduction of compressor power consumption is expected due to lower friction losses and therefore an increase of compressor efficiency (i.e. the same cooling capacity with lower power input). This means e.g., as a general result, that a drying time and an energy consumption of the drying cycle are reduced.

To also achieve or to support the above mentioned advantages of the embodiment having an oil quantity within the compressor of between 150 cc and 210 cc, the oil preferably has a kinematic viscosity. A mixture viscosity between 1.5 mm2/s (cSt) and 4 mm2/s is preferred, in particular at the heat pump dryer working point. The heat pump dryer working point may e.g. have a pressure of about 26 bar (having a condensation pressure at 70°C) and a mix temperature of oil and R290 of 80°C. That range of viscosity with higher values than previously used oils is preferred in order to assure good internal leakage sealing in the compressor (which is particularly preferred due to low density of R290) and therefore to improve compressor volumetric efficiency. These high values of kinematic viscosity lead to higher friction losses (negative effect in compressor efficiency). The overall situation is that the compressor efficiency is improved when oils with high kinematic viscosity are used.

Preferred for use in the compressor are Polyalkylene Glycols ("PAG") and Polyolester Oils ("POE"). Particularly preferred are the following oil types of the compressor, or their equivalents: (i) PAG PZ100S (from Idemitsu Kosan Co., Ltd.) having a mixture viscosity of 3.8 mm2/s (cSt) and a 30% solubility and (ii) POE RB-P68EP (from JX Nippon Oil & Energy Corporation) with 1.6 mm2/s and 24% solubility. The values refer to working parameters of the heat pump dryer at its working point, namely a pressure of about 26 bar (having a condensation pressure at 70°C and a mix temperature with R290, for example, of 80°C). These oils have the advantage that they exhibit an advantageous value of oil kinematic viscosity that is preferred in order to assure good internal leakage sealing in order to improve compressor volumetric efficiency and therefore improve compressor efficiency. They have the additional advantage that they have a relatively low solubility with the refrigerant compared to other typically used oils of the same types, like POE RB-68EP in heat pump dryer compressors.

Tablel shows a comparison among different oils mixed with R290 under the above mentioned conditions:

It is yet another preferred embodiment that a refrigerant of the vapour compression system of the heat pump is a flammable refrigerant, in particular R290 (propane). However, any other suitable flammable refrigerant may be used, e.g. R-1270 (propylene).

It is another preferred embodiment that propane (R290) is used as a refrigerant in conjunction with a condenser coil of the tube-and-fins type with the tubes having an outer diameter of 5 mm. The evaporator coil is also of the tube-and-fins type with the tubes hav- ing an outer diameter of 7 mm. The rotary compressor has a displacement smaller than 9.5 cc and higher than 6 cc. The compressor comprises a roller having a height-to-radius ration between 1.40 and 1.20. An area of the discharge port of the compressor is larger than 19.8 mm2. A quantity of oil in the compressor is between 150cc and 210cc. The following variants are particularly preferred: the type of oil is PAG PZ100S from Idemitsu Kosan Co., Ltd. (or an equivalent); the type of oil is POE RB-P68EP from JX Nippon Oil & Energy Corporation (or an equivalent). The transversal spacing of the tubes of the condenser coil is less than 21 mm while the longitudinal spacing is less than 19 mm. It is particularly preferred that the transversal spacing of the tubes of the condenser coil is about 19 mm (e.g. 19.05 mm) while the longitudinal spacing is about 16.5 mm. By using a condenser coil with tubes having an outer diameter of 5 mm a 12% lower internal volume within the condenser coil occupied by the refrigerant is achieved in comparison with 7 mm tubes. The less inner volume exists, the less refrigerant mass is needed to fill the condenser coil. The smaller outer diameter of 5 mm also translates into an improvement of dryer performance, namely a drying time reduction of 13% and a reduction in energy consumption of 11 %. In order to achieve a similar dryer performance (i.e. the same drying time and a 4% higher energy consumption) using a condenser having 7 mm tubes, 210 g of R290 is needed. In this case, the IEC 60335-2-11 standard would be infringed. The object of the invention is also achieved by a household appliance comprising the heat pump as described above. The laundry treatment appliance may in particular be a laundry dryer, e.g. as a stand-alone apparatus or as a washing/drying combination. The household appliance may also be a washing machine, a dishwasher, a cooling apparatus etc. Generally, the invention allows using vapour compression or heat pump laundry dryers with hydrocarbons or any other flammable fluid as refrigerant having a low charge and a high efficiency. Conventional solutions use a high volume in the refrigerant circuit (known solutions use 9.52 mm, 8 mm or 7 mm outer tube diameter heat exchangers with refrigerant loads higher than 190 g) and a high quantity of oil which has a high solubility with the refrigerant. With the restriction imposed by IEC 60335-2-11 of 150 g for flammable refrigerants it is not possible for the conventional solutions to have enough subcooling. This is due to a lack of refrigerant in the condenser coil which is the part of the cooling circuit which has the highest inner volume and consequently the highest amount of refrigerant. Using a condenser coil with an outer diameter smaller than 7 mm (i.e. 5 mm), the inner volume of the condenser is decreased so that for the same mass of refrigerant a higher density of refrigerant is obtained within the condenser coil. It follows that a higher percentage of liquid of the liquid-vapour phase of the refrigerant is obtained which in turn leads to an earlier condensation of the refrigerant in the condenser. Thus, a higher subcooling is achieved which benefits the cooling capacity. Furthermore, the use of a lower quantity of oil having a lower miscibility with the refrigerant allows for a lower amount of refrigerant mixed with the oil inside the compressor. Thus, a higher amount of refrigerant is available in the heat exchangers for heat transfer purposes. In addition, a proper design of compressor geometry (i.e. roller dimensions and discharge port area) improves the compressor efficiency by reducing friction loses and increasing a volumetric efficiency.

For a laundry dryer this leads to a reduced energy consumption (in the range of e.g. 12% to 17%, in particular 14.5%) which gives a lower value of TEWI (Total Equivalent Warming Impact). Furthermore, the drying time is reduced about 20.8%.

In the figures of the attached drawing, the invention is schematically shown by means of an exemplary embodiment, and will be explained further subsequently with reference to that exemplary embodiment. In particular,

Fig.1 shows a schematic drawing of a household tumble dryer using a heat pump;

Fig.2 shows a cross-sectional top view of a condenser;

Fig.3A shows a frontal view of the condenser of Fig.2; Fig.3B shows a frontal view of hairpin tubes of the condenser of Fig.3A; Fig.3C shows a frontal view of bent sections of the condenser of Fig.3A; shows a top view onto an opened rotary compressor; and

Fig.5 shows a cross-sectional side view of the opened rotary compressor of Fig.4. Fig.1 shows a laundry treatment appliance in form of a household tumble dryer H. The tumble dryer H comprises a heat pump P having at least a compressor 1 , a condenser 2 of a tube-and-fins type, a restrictor 3, and an evaporator 4 of a tube-and-fins type as elements. The elements 1 to 4 are serially connected in the shown order by refrigerant pipes 5 to form a refrigerant circuit or path.

The tumble dryer H also comprises a process air circuit or path 6 wherein process air A flows. The air circuit 6 comprises a rotatable drum 7 for holding laundry to be processed. The air A leaves the drum 7 at a medium temperature and wet. The air A then flows to the evaporator 4 that is placed in the air circuit A downstream the drum 7 and works as a heat exchanger. At the evaporator 4 the air A is cooled down and condenses. The resultant condensate is collected in a water tank W. At the evaporator 4, the air A also cools down and transfers part of its thermal energy upon the evaporator 4 and thus onto the refrigerant R within the evaporator 4. This enables the evaporator 4 to transform the refrigerant R from a liquid state into a vaporous state.

Further downstream the air circuit 6 the now dry and cool air A passes through the condenser 2 where a heat transfer from the condenser 2 and the refrigerant R, resp., to the air A is effected to heat up the air A and cool down the refrigerant R to its liquid state. The then warm and dehumidified / dry air A is subsequently reintroduced into the drum 7 to warm up the clothes and to pick up moisture. The refrigerant R is moved within the refrigerant circuit 1 to 5 by the compressor 1. The refrigerant R is a flammable refrigerant, in particularly R290. An amount of the flammable refrigerant R is 150 g or less. The evaporator 4 and the condenser 2 are thus used as heat exchangers.

The working of such a tumble dryer H with its heat pump P (comprising the refrigerant circuit 1 to 5) and its air circuit 6 is well known and does not need to be explained in greater detail.

Fig.2 shows a sectional top view onto a condenser 2 of the expanded tube and fins type. The condenser 2 comprises five hairpin tubes 8 of basically the same 'U'-shape that have the same orientation and are aligned in the same direction. Although the hairpin tubes 8 are shown in the same plane for the sake of simplicity, they are generally arranged in a three-dimensional structure. The hairpin tubes 8 are mechanically and thermally connected to a connection structure formed by a stack of fins 9. At its frontal side F and its rearward side B, the stack of fins 9 is covered by a respective end plate 10 for mechanical protection. Straight legs 1 1 of the hairpin tubes 8 penetrate the fins 9 in a perpendicular fashion. Thus, the bends or bent sections 12 of the hairpin tubes 8 are all situated on one side of the stack of fins 9 while (open) ends 13 of the hairpin tubes 8 are all situated on the other side of the stack of fins 9. The stack of fins 9 provides stiffness to the condenser 2 and restricts relative movement of the hairpin tubes 8. Thus, the stack of fins 9 restricts or dampens a propagation of externally induced forces and movements to elements of the condenser 2.

The hairpin tubes 8 are connected to form an open-ended fluid channel. To this effect, the hairpin tubes 8 are connected in pairs such that intermediate hairpin tubes 8 are connected to a respective hairpin tube 8 on both ends 13 and two terminal (or terminally located) hairpin tubes 8 are each connected to an intermediate hairpin tube 8 on only one end 13. The other end 13 of each terminal hairpin tube 8 is not connected to a hairpin tube 8 but to respective refrigerant lines 5.

The connection between the hairpin tubes 8 is effected using tubes in form of tube elbows 14 that are bent 180° ('U'-shaped or 'C'-shaped pipe elbows 14). The tube elbows 14 are attached to the open ends 13 of the hairpin tubes 8 e.g. by brazing or soldering, in particular flame brazing or flame soldering, to achieve a particularly durable, compact and cost- effective connection. The hairpin tubes 8 and/or tube elbows 14 may be made of the same material, e.g. aluminium or copper. Alternatively, as indicated, the hairpin tubes 8 and/or tube elbows 14 may be made of different materials, e.g. aluminium (shown without hatching) and copper (shown with hatching). The hairpin tubes 8 and/or tube elbows 14 have an outer diameter of 7 mm of less, practically neglecting possible expanded end sections where hairpin tubes 8 and tube elbows 14 are stuck together. Here, the hairpin tubes 8 and/or tube elbows 14 have an outer diameter dc of 5 mm. Thus, a meander-like condenser coil 8, 14 of a tube-and-fin type is formed. By means of the refrigerant lines 5, flammable refrigerant R, e.g. R290, may be introduced into and discharged from the condenser coil 8, 14 as indicated by the straight arrows. Fig.3A shows a frontal view of the condenser 2 of Fig.2 in the direction F of Fig.2 onto the condenser 2, now showing eight instead of five the hairpin tubes 8. The frontally projecting 'U' shaped or 'C shaped pipe elbows 14 of outer diameter dc of 5 mm are depicted as shown in Fig.3B while the hairpin tubes 8 of outer diameter dc of 5 mm with their rearward projecting bent sections 12 are depicted as shown in Fig.3C. The hairpin tubes 8 and/or tube elbows 14 may again be made of different materials, e.g. aluminium (shown without hatching) and copper (shown with hatching). The condenser 2 has a three-dimensional structure for good thermal exchange and for easy placement in the tumble dryer H.

The straight legs 11 of the hairpin tubes 8 are arranged in parallel columns C. Neighbour- ing columns C have a longitudinal distance or spacing dL of 19 mm or less. A transversal distance or spacing dT between neighbouring straight legs 11 of the same column C is 21 mm or less. In particular, a transversal spacing dT is 19.05 mm and a longitudinal spacing dL is 16.5 mm. The same basic structure as shown in Fig.2 and Figs.3A to 3C may also apply to the evaporator 4. However, the hairpin tubes 8 and/or tube elbows 14 of an evaporator coil may preferably have a larger outer diameter than those of the condenser coil 8, 14, e.g. 7 mm. Fig.4 shows a top view onto an opened rotary compressor 1 of the household tumble dryer H. Fig.5 shows a cross-sectional side view of the opened rotary compressor of Fig.4.

The compressor 1 comprises an outer cylinder 15 with a cavity 15a which houses a cylindrical roller 16. The roller 16 is supported by an end face 17 of the outer cylinder 15. The roller 16 can move or slip along the end face 17. A longitudinal axis L1 of the outer cylinder 15 and a longitudinal axis L2 of the roller 16 are aligned in parallel but spaced apart. The roller 16 is rollingly rotated within the outer cylinder 15 by a shaft 18 that is connected to an electrical motor (not shown). The shaft 18 lies concentric to the outer cylinder 15 and is thus eccentric to the roller 16. To be able to rotate the roller 16 within the outer cylinder 15, the shaft 18 has a laterally positioned cam 19 (only shown in Fig.5) that presses the roller 16 onto an inner side wall 20 of the outer cylinder 15. The roller 16 thus has a contact point K with the inner side wall 20. When the shaft 18 rotates it rolls the roller 16 along the side wall 20. A path of the contact point K at the inner side wall 20 then describes a closed ring. A displacement of the compressor 1 for one full rotation is between 6 cc and 9.5 cc.

The shaft 18 is formed as a hollow cylinder such that is can be connected to an oil pump (not shown) to feed oil into the compressor 1. The oil quantity within the compressor 1 is between 150 cc and 210 cc, preferably 180 cc or less. The oil may in particular be PAG PZ100S with 100 cSt or POE RB-P68EP with 68 cSt or an equivalent.

Into the cavity 15a of the outer cylinder 15 protrudes a blade 21. The outer cylinder 15 also has a suction port 22 leading through its wall to suck refrigerant into the cavity 15a and a discharge port 23 leading through the end face 17 to discharge the refrigerant. An area Q of the discharge port 23 is 19.8 mm ² or higher, preferably larger than 19.8 mm ² , preferably 20 mm ² or larger, preferably 21 mm ² or larger. For operation of the compressor, a cover lid (not shown) is put onto the open side of the outer cylinder 15. The cover lid may have a bushing for the shaft 18.

In Fig.5, a shown ratio of a height h to a radius r to an outer face of the roller 16 (the 'height-to-radius ratio' is between 1.4 and 1.2, preferably less than 1.4.

Of course, the invention is not restricted to the embodiments shown. LIST OF REFERENCE NUMERALS

1 compressor

2 condenser

3 restrictor

4 evaporator

5 refrigerated line

6 process air circuit/path

7 rotable drum

8 hairpin tube

9 fin

10 end plate

11 straight leg of hairpin tube

12 bend or bent section of hairpin tube

13 end of hairpin tube

14 tube elbow

15 outer cylinder

15a cavity of outer cylinder

16 roller

17 end face of outer cylinder

18 shaft

19 cam

20 inner side wall of the outer cylinder

21 blade

22 suction port

23 discharge port

A process air

B rearward side

C column of tubes

dL longitudinal distance or spacing

dT transversal distance or spacing

F frontal side h height

H tumble dryer

K contact point

L1 longitudinal axis of the outer cylinder L2 longitudinal axis of the roller

P heat pump

Q area of discharge port

r radius of the roller

R refrigerant

W water tank