EP3068940A1

EP3068940A1 - Heat pump laundry dryer

Info

Publication number: EP3068940A1
Application number: EP13789362.4A
Authority: EP
Inventors: Stefano Zandona'; Francesco Cavarretta
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2013-11-13
Filing date: 2013-11-13
Publication date: 2016-09-21
Anticipated expiration: 2033-11-13
Also published as: PL3068940T3; EP3068940B1; CN105658866A; AU2013405474B2; WO2015070901A1; CN105658866B

Abstract

The invention relates to a laundry dryer (1) comprising: a casing (2) supporting a drying chamber (3) for receiving a load to be dried; a process air conduit (11) in communication with the drying chamber (3) where a process air stream is apt to flow, a heat pump (30) having a heat pump circuit in which a refrigerant (R) can flow, said heat pump circuit including a first heat exchanger (31) where the refrigerant is cooled off and the process air stream is heated up, and a second heat exchanger (32) where the refrigerant is heated up and the process air is cooled off; said first and/or second heat exchanger being thermally coupled to the process air conduit (11) to perform heat exchange between said refrigerant flowing in said heat pump circuit and said process air stream; said first and/or second heat exchanger (31;32) further comprising a first (10) and a second heat exchanger module (10'), each module (10; 10') including an inlet header (5; 5') to direct a flow of said refrigerant (R) into said module (10, 10'); an outlet header (6; 6') to discharge said refrigerant (R) from said module (10, 10'); and a plurality of heat exchange layers (8; 8') fluidly connecting said inlet (5; 5') to said outlet header (6; 6') to enable said refrigerant (R) to flow from said inlet to said outlet header and/or vice versa; said layers (8; 8') being stacked one above the others in a predetermined stacking direction (Z; Z') and each layer (8; 8') including a plurality of channels (7); wherein said first and said second heat exchanger modules (10,10') are mounted adjacent one to the other and a first heat exchange layer (8) of the first module (10) and a second heat exchange layer (8') of the second module (10) are separated by a gap (g) in a direction incident to said stacking direction (Z, Z'), said first and said second heat exchanger modules (10, 10') including a plurality of fins (50) arranged on both said first and said second heat exchange layers (8, 8') and extending through said gap (g).

Description

Heat pump laundry dryer

Field of the invention

The present invention relates to a laundry dryer including a heat pump, in particular to a laundry dryer which optimizes the energy consumption and/or the duration of the drying cycles.

Background art

Most dryers consist of a rotating drum called a tumbler, thus called tumble dryer, through which heated air is circulated to evaporate the moisture from the load. The tumbler is rotated around its axis. Known laundry dryers include two categories: condense laundry dryers and vented laundry dryers. Dryers of the first category circulate air exhausted from the drum through a heat exchanger/condenser to cool the air and condense the moisture; they subsequently recirculate the air back through the drum, after having heated the same using a heater. Dryers of the second category draw air from the surrounding area, heat it, blow it into the drum during operation and then exhaust it through a vent into the outside.

Generally, dryers of the first category are the most common in the market, due to the fact that they do not require special means for proper installation such as an exhaust duct to exhaust the humid hot air coming from the drum. However, commonly, for the same power and the same amount of load, the drying cycle of a condensed dryer is longer than an equivalent cycle in a vented dryer.

Several solutions have been proposed according to the prior art in order to improve the efficiency of condense and vented dryers. In particular, heat pump technology has been applied to laundry dryer in order to enhance the efficiency in drying clothes. In traditional heat pump drier, air flows in a close loop. The air, moved by a fan, passes through a drum removing water from wet clothes, and then it is cooled down and dehumidified in a heat pump evaporator and heated up in a heat pump condenser to be re-inserted into the drum. In order to function, the heat pump includes a refrigerant with which the air is in thermal exchange, and the refrigerant is compressed by a compressor, condensed in the condenser laminated in an expansion device and then vaporized in the evaporator. EP 1209277 discloses a heat-pump clothes drying machine in which the motor used to drive the drum holding the clothes to be dried is also connected to a first fan, which circulates the drying air, as well as a second fan that cools the compressor.

US 201 1 /0280736 relates to a control method of a dryer. A control method of a dryer including a heat pump having a variable velocity type compressor, the control method includes steps of selecting at least one course supplying air or dried air; increasing an activation velocity of the compressor to a target velocity, as the selected course is implemented; and adjusting an open degree of an expansion valve provided in the heat pump. Summary of the invention

The present invention is relative to a laundry dryer for drying clothes and other garments including a heat pump having first and second heat exchangers. The laundry dryer of the invention may include either a vented or a condense dryer. The configuration of the heat exchangers in the laundry dryer of the invention is such that an optimal heat transfer capacity is achieved, substantially tailored on the specific geometry of the laundry dryer. Preferably, according to the layout of the internal component(s) of the laundry dryer, in particular preferably of the air circuit and of the optional fan, an optimized geometry of the heat exchanger(s) for maximizing the heat exchange between the refrigerant and the process air of the laundry dryer having that specific air circuit layout is obtainable according to the invention.

A heat pump dryer includes a drying chamber, such as a drum, in which the load, e.g., clothes, to be dried is placed. The drying chamber is part of a process air circuit; in particular a closed-loop circuit in case of a condensed dryer or an open circuit in case of a vented dryer, which in both cases includes an air duct for channeling a stream of air to dry the load. The process air circuit is connected with its two opposite ends to the drying chamber. Preferably, hot dehumidified air is fed into the drying chamber, flowing over the laundry, and the resulting humid cool air exits the same. The humid air stream rich in water vapor is then fed into an evaporator of a heat pump, where the moist warm process air is cooled and the humidity present therein condenses. The resulting cool dehumidified air is then either vented outside the dryer in the ambient where the latter is located or it continues in the closed-loop circuit. In this second case, the dehumidified air in the process circuit is then heated up before entering again in the drying chamber by means of a condenser of the heat pump, and the whole loop is repeated till the end of the drying cycle. Alternatively, ambient air enters into the drum from the ambient via an inlet duct and it is heated up by the condenser of the heat pump before entering the drying chamber.

The heat pump of the apparatus includes a refrigerant circuit in which a refrigerant can flow and which connects via piping a first heat exchanger or condenser, a second heat exchanger or evaporator, a compressor and a pressure-lowering device. The refrigerant is pressurized and circulated through the system by the compressor. On the discharge side of the compressor, the hot and highly pressurized vapor is cooled in the first heat exchanger, called the condenser, until it condenses into a high pressure, moderate temperature liquid, heating up the process air before the latter is introduced into the drying chamber. The condensed refrigerant then passes through the pressure-lowering device such as an expansion device, e.g., a choke, a valve or a capillary tube. The low pressure liquid refrigerant then enters the second heat exchanger, the evaporator, in which the fluid absorbs heat and evaporates due to the heat exchange with the warm process air exiting the drying chamber. The refrigerant then returns to the compressor and the cycle is repeated.

In some embodiments, in the first and/or second heat exchangers, the refrigerant may not be subject to a phase transition.

In the following, with the terms "downstream" and/or "upstream", a position with reference to the direction of the flow of a fluid inside a conduit is indicated. Additionally, in the present context, the terms "vertical" and "horizontal" are referred to the positions of elements with respect to the dryer in its normal installation or functioning. Indeed, a horizontal plane (X",Y") formed by two horizontal X,Y perpendicular directions is defined, and a vertical direction Z", perpendicular to the horizontal plane, is defined as well in a 3-D space.

Applicants have considered a heat pump dryer wherein the first and/or the second heat exchanger of the heat pump includes one or more heat exchanger modules realized as follows. Each heat exchanger module includes two headers, an inlet header to allow the inflow of refrigerant into the module and an outlet header to allow the refrigerant to discharge from the module. Additional headers can be included as well as additional inlet and/or outlet headers. Further, the module includes a plurality of heat exchange layers stacked in a stacking direction (e.g., the layers are disposed one above the other(s) along a given direction). Although often the terms "one above the other in a stacking direction" is mentioned, this does not mean that the heat exchange layers are disposed one above the other(s) along a vertical direction. It simply means that along the given direction (the stacking direction) the layers are disposed in a sequence one above the other(s), although the stacking direction could be also a horizontal one.

Each heat exchange layer includes more than one channel for the refrigerant flow, the channels being located one adjacent to the other(s) within the layer. The channels are in fluid communication with the inlet and/or the outlet header so that the refrigerant is allowed to flow from the inlet to the outlet header and/or vice versa. Preferably, the plurality of channels is parallel to each other within each heat exchanger layer. Each heat exchange layer defines two opposite ends: the ends are fixed to the inlet and/or outlet header, or to an additional layer (e.g. the layer above and/or below).

Within each heat exchange layer, the channels can also be angled or they can have an irregular shape. Preferably, the stacking direction is a vertical direction and the heat exchange layers are vertically stacked one above the other(s).

The heat exchange layers have a given width which depends on the number of channels realizing the layer, and a longitudinal extension, which corresponds to the longitudinal extensions of the channels within the layer forming the same. The width and the longitudinal extension direction preferably define a plane. This plane might be perpendicular to the stacking direction of the layers, or it can form an angle with the same. Alternatively, the heat exchange layers may be tilted one with respect to the other or may form arches one above the other(s).

Channels of neighboring (i.e., adjacent in the stacking direction) layers in the stacking direction are connected by fins.

The inlet and outlet headers may be at a given distance from each other, so that each heat exchange layer is connected with one end to the inlet and with the opposite end to the outlet headers, respectively, e.g., the heat exchange layers are interposed between the inlet and the outlet headers. Alternatively, the inlet and outlet headers can be located one in contact or adjacent to the other (for example one on top of the other), so that the heat exchange layers are attached with one end to the inlet or to outlet header and with the opposite end to an additional intermediate header, located at a given distance from the inlet and outlet headers. Also in this case, each heat exchange layer is connected with one end to the inlet or outlet header and with the other end to the additional header, so that each layer is still always interposed between two headers. In the first case, the refrigerant in order to reach the outlet header from the inlet one passes through a single heat exchange layer, while in the second case from the inlet header the refrigerant has to flow through at least two heat exchange layers, and the flow has one direction in a layer and substantially the opposite direction in the other layer of the two, in order to reach the outlet header. In a different additional embodiment of the heat exchanger module, the inlet and the outlet headers are each connected to a single layer of the plurality. For example, the inlet header might be connected to a free end of the topmost (or lowermost) layer of the plurality along the stacking direction and the outlet header may be connected to a free end of the lowermost (or topmost) layer. Each other layer of the plurality, with the exclusion of the topmost and lowermost, is then connected to its respective neighboring layers (located above and below) through their ends, which form bends which connect one end of one layer to the end of the neighboring one. In this way, a single set of channels form all layers and the set of channels folds several times forming a zigzag pattern.

In all embodiments, the plurality of channels is subjected to, at least in part, the process air stream so that there is heat exchange between the refrigerant flowing within the channels and the process air. For this purpose, therefore, at least partially, preferably for their whole extension, the channels of the heat exchange layers of the modules of the first and/or second heat exchanger are preferably located within an air duct, part of the process air circuit. The headers have the function of holding the various layers and/or as an inlet and/or outlet for the refrigerant into the module.

Applicants have realized that the process air flowing in the air circuit of know laundry dryers is not spatially uniform, in other words, it does not have a uniform spatial flow rate within the air conduit. Taking a cross section of the air conduit in any location of the same, the air flowing through that section has in general different velocities in different points of the section and also the flow rate is different in different areas of the section. Moreover, the direction of flow of the air is also not always parallel to walls of the air conduit. The flow lines of the process air stream can follow complex patterns within the air conduit, including vortex and turbulence.

This non-uniformity is due to the construction of the air conduit itself: process air inside a laundry dryer is not commonly flowing along straight ducts, on the contrary there are several bends and curvatures in the conduit as well as elements, such as for example a lint filter, which the process air flow has to traverse and which may cause turbulence and flow deviations.

As an example, in some dryers, the process air exits the drying chamber through an aperture realized in the boundary of a door of the casing and it bends downwards passing through a filter to collect lint. Furthermore, the process air bends again to flow within the basement of the casing, wherein there is generally available space to locate the heat exchanger(s) of the heat pump.

In other dryers, the process air exits the drying chamber through apertures realized in the chamber itself in the uppermost region of the same and returns in the chamber via apertures realized in a lowermost region of the chamber, the process air thus flowing on the top region of the casing of the laundry dryer where the heat exchangers are located in order to exchange heat with the process air.

Furthermore, generally, in an air conduit a fan is present in order to blow process air forcing the circulation of the same along the air circuit itself. Again, due to constrains imposed by the casing limited volume and the presence of several elements inside the latter, the fan is not always located centrally with respect to the air conduit, but it might be off-center implying that it blows air closer to one (or more) of side walls of the conduit than to the other(s). Thus, this off-centering of the fan also causes an asymmetry in the flow rate of the process air through the air conduit.

Due to the fact that the heat exchange takes place mainly in the channels forming the heat exchange layers, and in the fins connecting the stacked heat exchange layers, Applicants have realized that the spatial non-uniformity of the process air flowing through the module and turbulence of the same also affects the heat exchange efficiency of the same. Another common problem in heat exchangers is that heat exchangers are generally designed to maximize the surface area between the two fluids which have to exchange heat, in this case the refrigerant and the process air, while minimizing resistance to fluid flow through the exchanger. Thus, in general, the heat exchanger modules are designed to have the widest possible heat exchange surface(s). However, in appliances such as dryers, there is a limited space for any component and therefore the maximization of the heat exchange surfaces have to be realized in the minimum possible total volume. The total area of the heat exchange surface is limited by the available volume for the module(s).

Applicants have realized that the geometry of the module can be optimized, without changing the overall structure of the module, which implies that the costs and manufacture complexity in building the module remains substantially unaltered. In other words, Applicants have realized that the available surface for heat exchange in a module can be increased keeping the overall occupied volume by the module the same, and at the same time the optimized geometry achieves a better control of the air flow through the heat exchanger modules. In order to maximize the heat exchange surface, Applicants have optimized the fins' geometry to obtain the maximum extension of heat exchange surface where the process air is flowing most. Applicants have found that connecting a first and a second adjacent heat exchanger modules with common fins, i.e., a layer of the first module and a layer of the second module share the same plurality of fins, at the same time both increases the available surface for heat exchange and reduces the turbulence of the air flow through the modules. The latter effect is due to the "tunneling" of the process air through the fins themselves which are relatively long (bridging two modules) in the direction of the air flow.

In the present context, a fin is an element including a surface that extends from an object (in this case a heat exchange layer) to increase the rate of heat transfer by increasing convection.

Adding a fin to an object, in this case to a surface of the heat exchange layer, increases the surface area for the heat exchange. Fins of any type and geometry can be applied to the present invention. Preferably, the fins are interposed between two adjacent vertically stacked heat exchange layers of the module. Fins can be present among each couple of adjacent heat exchange layers, or only among some of them.

Fins include walls which form the heat exchange surface. According to a first aspect, the invention relates to a laundry dryer comprising: a. a casing supporting a drying chamber for receiving a load to be dried; b. A process air conduit in communication with the drying chamber where a process air stream is apt to flow; c. A heat pump having a heat pump circuit in which a refrigerant can flow, said heat pump circuit including a first heat exchanger where the refrigerant is cooled off and the process air stream is heated up, and a second heat exchanger where the refrigerant is heated up and the process air is cooled off; said first and/or second heat exchanger being thermally coupled to the process air conduit to perform heat exchange between said refrigerant flowing in said heat pump circuit and said process air stream; said first and/or second heat exchanger further comprising a first and a second heat exchanger module, each module including

^■ An inlet header to direct a flow of said refrigerant into said heat exchanger module;

^■ an outlet header to discharge said refrigerant from said heat exchanger module; and

^■ a plurality of heat exchange layers fluidly connecting said inlet to said outlet header to enable said refrigerant to flow from said inlet to said outlet header and/or vice versa; said layers being stacked one above the others in a predetermined stacking direction and each layer including a plurality of channels; characterized in that said first and said second heat exchanger modules are mounted adjacent one to the other and a first heat exchange layer of the first module and a second heat exchange layer of the second module are separated by a gap in a direction incident to said stacking direction, said first and said second heat exchanger modules including a plurality of fins arranged on both said first and said second heat exchange layers and extending through said gap.

According to the invention, the first and second heat exchanger modules, which can belong to the same heat exchanger (e.g. both to the first heat exchanger or both to the second heat exchanger), or to different heat exchangers (e.g. the first module may belong to the first heat exchanger and the second module to the second heat exchanger), are located one adjacent to the other. A gap is present between a first layer of the first module and a second layer of the second module. Generally, a gap is present because the layers of one module cannot be put in contact to the layers of the adjacent module. This is due for example to the dimensions of the headers, which are commonly broader than the width of the layers, or to other constraints. Thus, although the layers of the first module are located adjacent to those of the second module, a - even minimal - spacing or gap between the two set of layers is present. The dimension of the gap is defined in the following way. Both the first and the second layers include a first and second boundary rim, respectively, one facing the other. The distance between the first and the second rim is the gap's dimension or length. The gap dimension does not have to be uniform: the first and second heat exchanger modules can be either parallel, e.g. having parallel layers one to the other, so that the gap between the first and the second layers is substantially constant all along the external rims of the first and the second layers facing one the other, or angled one with respect to the other, so that the distance between the first and second rim continuously varies along the rims' extension.

This gap's dimension is, in other words, the distance which separates, along a direction, the two heat exchange modules. The fact that the gap defines a direction means that the gap extends, i.e. it forms a line connecting the first layer and the second layer, along a line which is not parallel to the stacking direction, on the contrary it is incident to the latter. This in turn means that the first and second heat exchanger modules are not located one above the other along the stacking direction. According to the invention, a plurality of fins connects the first and the second heat exchanger modules, the fins being arranged on the first heat exchanger layer of the first module and on the second heat exchanger layer of the second module. The plurality of fins is also present through the gap between the first and second layers, forming a bridge from the first module to the second one. For example, in an embodiment, a fin of the plurality includes a wall and this wall is located on top of an upper surface of the first layer and on top of an upper surface of the second layer and it extends also through the gap as a single element. Using this geometrical configuration, the heat exchanger(s) of the invention occupies the same overall volume than a heat exchanger having two modules each having fins between the layers of the module itself (not extending to the adjacent module), but at the same time it presents a wider heat exchange surface. The increased surface includes the portion of the fins which extend through the gap between modules. At the same time, the walls of the fins forms "tunnels" guiding the process air through the modules and minimizing the turbulence. Indeed, having long "tunnels" formed by the fins, tunnels which are not interrupted by the end of the module, allows a greater uniformity in the air distribution within the air conduit where the modules are located. The presence of common fins on two modules improves additionally the mechanical resistance of the single unit for med by the two modules themselves which are fixed one to the other by the fins. The mounting of such a unit in the air conduit of the dryer is simplified, because a single unit, instead of two, has to be positioned and aligned.

It is to be understood that more than two modules can be connected by the same plurality of fins. For example if a first a second and a third heat exchanger modules are all mounted adjacent one to the other(s), a single plurality of fins can be located on a layer of each module and can extend in this case through two gaps, one present between the first and the second module and a second present between the second and third module.

This construction is applicable to any number N of adjacent modules. In the above mentioned aspect, the following additional characteristics can be present, alternatively or in combination.

According to a preferred embodiment, said first module includes a third heat exchange layer forming together with said first heat exchange layer a first couple of adjacent heat exchange layers in said stacking direction and said second module includes a fourth heat exchange layer forming together with said second heat exchange layer a second couple of heat exchange layers in said stacking direction, said plurality of fins being arranged between the first and third layers and between the second and fourth layers of said first and of said second couple, respectively.

Thus, each module includes at least a couple of adjacent heat exchanger layers along the stacking direction. The plurality of fins is interposed between the layers of a first couple of such adjacent layers of the first module and between the layers of a second couple of such adjacent layers of the second module. In the invention, instead of having a plurality of fins between the layers of the first couple and a separated plurality of fins between the layers of the second couple, includes a single plurality and the fins from the first module "extend" reaching the second module, in other words the same plurality of fins connects the adjacent layers of the first couple on the first module and the second couple of adjacent layers in the second module.

In an advantageous embodiment, a distance between the first and third adjacent heat exchange layers of the first couple and a distance between the second and fourth adjacent heat exchange layers of said second couple are substantially identical. In this way, the plurality of fins stays uniform in dimension, e.g. in its extension from one module to the other, the plurality of fins can maintain not only for example the same pitch but also the same height, without requiring special modifications. Standard fins can thus be used.

More preferably, said plurality of fins defines a height in said stacking direction, said height being substantially equal to the distance present between the first and third heat exchange layers or to the distance present between the second and fourth heat exchange layers of said first or said second couple, respectively.

The fins thus occupy all the available space between the couple of adjacent layers of each module maximizing the heat exchange surface they define. Advantageously, said gap is present in a direction substantially perpendicular to said stacking direction.

The first and second modules are preferably disposed one after the other in the direction of flow of the process air within the air duct, and preferably are positioned parallel one to the other, so that the mounting is easier and the volume occupied minimized. More preferably, the gap direction is substantially a horizontal direction.

In a preferred embodiment, the length of said gap is preferably comprised between 5 mm and 50 mm.

Preferably, said first and second heat exchange layers have a first and a second width, respectively, the width of said plurality of fins being substantially equal to the sum of said first width, of said second width and of a length of said gap. Again, in order to maximize the heat exchange surface defined by the plurality of fins, the latter have a width which is as broad as possible, thus covering the whole width of the first layer, the whole width of the second layer and of the length of the gap therebetween.

In a favorite embodiment, said first and said second heat exchange module are located in an air duct of said air conduit, and said plurality of fins includes a plurality of walls, each wall defining a heat exchange wall surface extending from said first and/or second heat exchange layer, said walls being arranged so that a direction of flow of said process air flowing in said air duct is substantially parallel to said heat exchange wall surfaces.

The plurality of fins in this way defines a plurality of tunnels formed by the fins' walls which act as channeling means for the process air within the air conduit. The turbulence of the process air is thus minimized.

Preferably, said first and second heat exchanger modules are located in an air duct of said air conduit, said first and second modules and said air duct being reciprocally arranged so that a direction of flow of said process air flowing in said air duct is substantially perpendicular to said stacking direction.

The heat exchange layers in which the heat exchange takes place are located in a portion of the air circuit. It is preferable, in order to maximize heat exchange, that the process air stream flowing through the air duct "hits" the modules substantially in a perpendicular manner, i.e., in such a way that a module plane - defined by the module stacking direction and longitudinal extension - and the direction of the process air stream within the air duct are substantially perpendicular. In this way, air turbulence is minimized and heat transfer maximized. In case both first and second heat exchanger include a module, the preferred configuration is thus having the two modules substantially parallel within the air duct. More preferably, these two modules are also perpendicular to the longitudinal extension of the air duct.

Advantageously, said first and second heat exchanger module are located in an air duct of said air conduit, said air duct and said first and second modules being reciprocally arranged so that a direction of flow of said process air entering in said air duct is substantially parallel to said heat exchange layers. In this embodiment, the resistance encountered by the process air flowing through the modules is minimized due to the fact that the various heat exchange layers are parallel to the direction of process air flow itself.

The tunneling effect of the fins at the same time is optimal. Advantageously, said first and second heat exchanger modules are located in an air duct of said air conduit, said air duct and said first and second modules being reciprocally arranged so that that a direction of flow of said process air entering in said air duct is substantially parallel to said direction of said gap.

The modules are thus preferably located one after the other in the direction of flow on the process air so as to maximize the heat exchange.

Advantageously, the dryer includes a fan to circulate said process air within said air conduit.

Often, said fan is so configured to blow said process air in such a way that the spatial distribution of the flow rate of the process air through a transverse section of said air conduit is spatially asymmetrical, having a region of higher flow rate and a region of lower flow rate. This is generally due to the "non-central" position of the fan with respect to the air conduit. The non-uniformity is thus improved by the geometry of the plurality of fins.

Preferably, in said first and second heat exchanger modules a first longitudinal direction of the heat exchange layers of said first module and a second longitudinal direction of the heat exchange layers of said second module are defined, and said first and second longitudinal directions are substantially parallel to each other.

More preferably, said first and/or second heat exchanger modules are arranged so that said first and/or second longitudinal direction of said heat exchange layers is substantially perpendicular to a direction of flow of said process air inside said air duct. The geometrical location of the modules is optimized always in order to maximize the heat exchange and to minimize air turbulence within the air duct.

In a preferred embodiment, said inlet and outlet headers of said first and/or second heat exchange module are located one on top of the other along said stacking direction.

In a specific configuration, one or both of the first and second modules has an inlet and outlet header stacked one on top of the other. For example, the headers can be realized by the same pipe which is divided in two sections by a separator. Each section is not in direct fluid communication with the other section, the refrigerant has to flow through the layer(s) in order to reach from the inlet header the outlet header.

According to an advantageous embodiment, the cross-section of said inlet and/or said outlet header and/or said intermediate header is oblong, wherein its smallest diameter is smaller than a width of said layer.

Preferably, the headers of the heat exchangers' modules are oblong, e.g., they have an oval or rectangular cross section, in order to further reduce the internal volume of the exchangers, reducing space, and also in order to save some refrigerant. The refrigerant is indeed relatively expensive and it is preferred to minimize the same for a given heat exchange capacity. Moreover, the exchange surface (e.g., the total surface of channels layers and fins) can be increased since the portion of the process air duct used to place the header is reduced, so the extension of the channels can be increased. In one direction, the minimum dimension of the cross section is fixed: it has to be wide enough to be connected to one end of the layer and thus it has to be at least as wide as the layer. In the perpendicular direction, however, the maximum width, or diameter, can be reduced below the layers' width.

More preferably, said cross section of said inlet and/or said outlet header and/or said intermediate header is oval or rectangular. Advantageously, said channels have a hydraulic diameter smaller or equal than 5 mm.

According to an embodiment of the invention, the hydraulic diameter of each of the channel, where the hydraulic diameter D_H is defined as where A is the cross sectional area of the channel and P is the wetted perimeter of the cross-section of the channel, is smaller or equal than 5 mm, i.e. D_H ≤ 5 mm, more preferably D_H ≤ 3 mm, even more preferably D_H ≤ 1 mm.

Due to the size of the hydraulic diameter, the module of the invention may include many channels, therefore the refrigerant flow is divided in a plurality of smaller refrigerant streams, one per channel. In this way the pressure drop of the refrigerant within the channels is reduced compared to the refrigerant pressure drop in bigger channels. Additionally, it is known that the maximum pressure that a pipe can withstand is inversely proportional to its hydraulic diameter. A small hydraulic diameter therefore means that the channels can withstand higher pressures than bigger pipes. For this reasons, high pressures refrigerants, such as carbon dioxide, can be used in the heat pump circuit of the dryer of the invention.

Moreover, still due to the smaller size, a smaller amount of refrigerant is needed for the proper functioning of the module than in standard heat pump dryers. Use of hydrocarbons, which are flammable, can be therefore also considered, due to the low amount required.

The shape of the cross section of the channels is not relevant for the present invention, and it can be squared, rectangular, circular (in this case the hydraulic diameter coincide with the diameter of the circle), elliptic, and so on. The cross section of the plurality of channels does not have to be the same for all channels in the plurality, but it can be different and the various channels can have a combination of the possible above listed cross sections. In addition, the cross section may vary both in hydraulic diameter and/or in shape along the extension of the channel.

Preferably, said heat exchange layer includes a plurality of channels one parallel to the others.

Preferably, the channels extend along a direction which is substantially parallel to the horizontal plane and also perpendicular to the flow of the process air stream when the dryer is functioning. In other words, the channels, which preferably have a diameter much smaller than their length, extend from the first to the second header in such a way that their longitudinal extension results substantially parallel to the horizontal plane and perpendicular to the flow of process air with which the heat exchange takes place.

In case the channels are rectilinear, their longitudinal extension (and longitudinal direction) corresponds to their longitudinal axis. In case the channels are not rectilinear, for example they are forming an arch, their longitudinal extension (and longitudinal direction) corresponds to the line joining the point from which they depart from the inlet/outlet header and the first point having the maximum distance from the inlet/outlet header longitudinal axis. The channels may include rectilinear portions and/or bumps or other turbulence-inducing elements that may enhance the heat transfer between the refrigerant and the air process stream. Additionally, channels may include smooth or corrugated inner and/or outer surfaces and may comprise bends or curves.

In a preferred embodiment of the invention, the channels are rectilinear. In an additional embodiment of the invention, the channels include a plurality of rectilinear portions connected to each other via U-bends. In this latter embodiment, the rectilinear portions are preferably stacked one on top of the other in a vertical direction. According to a different embodiment of the invention, the rectilinear portions are coplanar, more preferably in a plane parallel to the horizontal plane. According to a further embodiment, the channels are bended forming an arch, their longitudinal extension being preferably still perpendicular to the process air flow. This latter embodiment is used in particular to place the module of the dryer of the invention in the most suitable location within the process air conduit. Indeed, it is known that there are portions of the process air conduit in which the process air flow is more uniform and less turbulent. Heat exchange between the process air flow and the refrigerant is therefore optimal in these locations. An arched channel allows the positioning of the module also in locations in which other objects are present or narrow thus in general to better exploit the available space and/or to reduce the limitations given by a not even distribution of the air flow.

Advantageously, said first heat exchanger includes more heat exchanger modules that said second heat exchanger. Brief description of the drawings

These and other features and advantages of the invention will better appear from the following description of some exemplary and non-limitative embodiments, to be read with reference to the attached drawings, wherein:

- Fig. 1 is a schematic view, where some elements have been removed for clarity, of a laundry dryer according to the invention;

- Fig. 2 is a perspective view of a portion of an embodiment of the dryer of the invention of fig. 1 with the casing removed;

- Fig. 3 is a perspective view in section of an element of the dryer of fig. 1 ;

- Figs. 4a and 4b are a schematic front view and top view, respectively, of an embodiment of the heat exchanger module of the dryer of the invention of fig. 1 ; - Figs. 5a and 5b are a schematic front view and top view, respectively, of a further embodiment of the heat exchanger module of the dryer of the invention of fig. 1 ;

- Figs. 6a and 6b are a schematic front view and top view, respectively, of a further additional embodiment of the heat exchanger module of the dryer of the invention of fig. 1 ;

- Figs. 7a and 7b are a schematic front view and top view, respectively, of an embodiment of connection between two heat exchanger modules, with some elements not depicted, of any of the examples of figs. 4a-4b to figs. 6a-6b;

- Figs. 8a and 8b are a schematic partially disassembled perspective and top view of a module of two modules of a laundry dryer not belonging to the invention;

- Figs. 9a, 9b and 9c are two schematic perspective views, the second of which partially disassembled, and a top view of two modules of a laundry dryer of the present invention of fig. 1 ;

- Fig. 1 0 is a cross section of a component of the laundry dryer of fig. 1 ; - Fig. 1 1 is an enlarged view of fig. 9c;

- Fig. 1 2 is a lateral view in cross section of the modules of figures 9a-9c; and

- Fig. 1 2a is an enlarged detail of fig. 12.

Detailed description of the preferred embodiments of the invention

With initial reference to fig. 1 , a laundry dryer realized according to the present invention is globally indicated with 1 .

Laundry dryer 1 comprises an outer box casing 2, preferably but not necessarily parallelepiped-shaped, and a drying chamber, such as a drum 3, for example having the shape of a hollow cylinder, for housing the laundry and in general the clothes and garments to be dried. The drum 3 is preferably rotatably fixed to the casing, so that it can rotates around a preferably horizontal axis (in alternative embodiments, rotation axis may be vertical or tilted). Access to the drum 3 is achieved for example via a door, preferably hinged to casing, which can open and close an opening realized on the casing itself. More in detail, casing 2 generally includes a front panel 20, a rear wall panel 21 and two sidewall panel all mounted on a basement 24. Panels 20, 21 and basement 24 can be of any suitable material. Preferably, the basement 24 is realized in plastic material. Preferably, basement 24 is molded. Preferably, basement 24 includes an upper and a lower shell (in fig. 2 only the lower shell 24a is visible).

The dryer 1 defines an horizontal plane (X", Y") which is substantially the plane of the ground on which the dryer is situated, and a vertical direction Z" perpendicular to the plane (X", Y"). Laundry dryer 1 also comprises an electrical motor assembly (not shown in the pictures) for rotating, on command, revolving drum 3 along its axis inside casing. Casing 2, revolving drum 3, door and motor are common parts in the technical field and are considered to be known; therefore they will not be described in details.

Dryer 1 additionally includes a process air circuit 4 which comprises the drum 3 and an air process conduit 1 1 , schematically depicted in fig. 1 as a plurality of arrows showing the path flow of a process air stream through the dryer 1 . In the basement 24, air process conduit 1 1 includes an air duct 1 1 a which is formed by the connection of the two upper and lower shells 24a. Air process conduit 1 1 is preferably connected with its opposite ends to two opposite sides of drum 3. Process air circuit 4 may also include a fan or blower 12 (see fig. 1 ) and an electrical heater (not shown in the figures).

The air duct 1 1 a can be integral with the basement 24 as depicted in fig. 2, or it can be a different element attached to the same. Moreover, the air duct 1 1 a can be located not only in the basement 24, but also in correspondence of a top or lateral part within the casing 2 of the laundry dryer 1 . The dryer 1 of the invention additionally comprises a heat pump 30 including a first heat exchanger called also condenser 31 and a second heat exchanger called also evaporator 32. Heat pump 30 further includes a refrigerant closed circuit (schematically depicted in the picture with lines connecting the first to the second heat exchanger and vice versa, see in detail fig. 1 ) in which a refrigerant fluid flows, when the dryer 1 is in operation, cools off and may condense in correspondence of the condenser 31 , releasing heat, and warms up, potentially even evaporating, in correspondence of the second heat exchanger (evaporator) 32, absorbing heat. Alternatively, no phase transition takes place in the condenser and/or evaporator, which indicates in this case respectively a gas heater and gas cooler; the refrigerant cools off or it warms up, respectively, without condensation or evaporation. In the following, the heat exchangers are named either condenser and evaporator or first and second heat exchanger, respectively.

More in detail, the heat pump circuit connects via piping 35 (visible in fig. 2) the second heat exchanger 32 where the refrigerant warms up and may undergo a phase transition from the liquid to the vapor via a compressor 33 to the first heat exchanger 31 , in which the refrigerant cools off and may condense again. The cooled or condensed refrigerant arrives via an expansion device 34, such as a choke, a valve or a capillary tube, back at the evaporator 32.

The condenser 31 and the evaporator 32 of the heat pump 30 are located in correspondence of the process air conduit 1 1 , at least partially. More preferably, they are located in correspondence of the air duct 1 1 a of basement 24. In case of a condense dryer - as depicted in fig. 1 - where the air process circuit 4 is a closed loop circuit, the condenser 31 is located downstream of the evaporator 32. The air exiting the drum 3 enters the conduit 1 1 and reaches the evaporator 32 which cools down and dehumidifies the process air. The dry cool process air continues to flow through the conduit 1 1 till it enters the condenser 31 , where it is warmed up by the heat pump 30 before re-entering the drum 3.

A lint filter 103 to block the lint is preferably present in the dryer 1 . The lint filter 103 is preferably located before the process air reaches the evaporator 32, e. g. when it exits the drum 3.

First and/or second heat exchanger 31 , 32 further include - according to a characteristic of the invention - one or more heat exchanger modules 10 located along the process air conduit 1 1 . In particular, as already mentioned, the first and the second heat exchangers 31 and 32, and thus module(s) 10, are located in the air duct 1 1 a. Thus the preferred location of the air duct 1 1 a within the casing 2 is within a volume of the same where enough space is available to host the modules 10. With now reference to fig. 2, the basement 24 of a dryer 1 showing a plurality of modules 10 included in the evaporator 32 and in the condenser 31 of the heat pump 30 according to the invention is depicted. In the mentioned figures, the casing 2 and the drum 3 of the dryer 1 have been removed in order to show the heat exchangers located along the process air conduit 1 1 , more specifically in air duct 1 1 a. As stated above, although in the appended drawings both evaporator 32 and condenser 31 of the dryer 1 include heat exchanger modules 10, it is to be understood that the evaporator 32 only or the condenser 31 only might include such module(s) 1 0. In addition, a single module 10 can be included in either evaporator 32 or condenser 31 . Moreover, in case both evaporator and condenser include more than one module 10 according to the invention, the evaporator can include a different number of modules from the condenser (as per the appended figure 2 where the evaporator 32 includes two modules 10 and the condenser four modules 10). Preferably, the condenser 31 includes more modules than the evaporator 31 . In case more than one module 10 is included in the dryer of the invention, the modules can be identical or different.

The structure of a single module 10 will be now be described, with reference to the different embodiments depicted in fig. 3, from 4a-4b to 6a-6b, 9a-9c, 1 1 .

With reference to fig. 3, where the depicted module is partially sectioned, a heat exchanger module 10 includes an inlet header 5 and an outlet header 6. Inlet and outlet headers 5, 6 have preferably the structure of a pipe. The headers have a longitudinal extension along an axis, which corresponds to the main direction of flow of the refrigerant within the headers. The refrigerant is flowing into the module 10 via the inlet header 5 and exiting the same via the outlet header 6. A plurality of channels, each indicated with 7, is fluidly connecting the inlet to the outlet header and vice versa, so that the refrigerant can enter and exit the module. The plurality of channels is subject to the flow of process air, i.e., channels 7 are located within the air duct 1 1 a of the dryer 1 . The channels 7, due to their configuration, allow a better heat exchange between the refrigerant and the process air than known dryers.

Channel 7 defines a longitudinal direction X along which it extends, which correspond to the longitudinal extension of the heat exchange layer 8. Preferably, the channels 7 are mounted in the module 1 0 so that their longitudinal extension X is substantially perpendicular to a process air flow direction. Preferably, their longitudinal extension is substantially parallel to the horizontal plane. In other words preferably, when mounted, the longitudinal direction X lies on a plane parallel to the (X", Y") plane defined by the dryer 1 . Preferably, the refrigerant flow within channels 7 is substantially perpendicular to the process air flow. However, depending on the direction of the process air flow, the direction of the process air stream and the direction of the refrigerant flow can alternatively form an angle therebetween. The channels 7 are grouped in heat exchange layers 8: each heat exchange layer includes a plurality of channels 7 which are preferably adjacent and parallel to each other. More preferably, each module 1 0 includes a plurality of heat exchange layers 8, more preferably all layers 8 are stacked one above the other(s) in a stacking direction Z and even more preferably parallel to each other, substantially forming a plurality of parallel rows. Preferably the stacking direction is the vertical direction, i.e., Z and Z" are parallel to each other. Alternatively, the stacking direction and the vertical direction can form an angle therebetween.

According to an embodiment of the invention, heat exchange layer 8 includes a single tube, having for example an elongated cross section, including two substantially parallel flat surfaces 9a, 9b. Within the tube, separators 8a are realized in order to longitudinally divide the interior of the tube in the plurality of channels 7. Such a structure is schematically depicted in the cross section of a heat exchange layer 8 of fig. 10. The cross section of the single channel 7 can be arbitrary. Each heat exchange layer 8 has a width W which depends on the number of channels which are located one adjacent to the other (see figures 4b and 5b).

Each couple of adjacent stacked heat exchange layers 8 of a module is connected via a plurality of fins 50. Preferably the upper surface 9a of a heat exchange layer 8 is connected via the plurality of fins 50 to the lower surface 9b of the adjacent heat exchange layer 8 (see for example fig. 4a). The geometry of the fins will be better detailed below. The width W of the layer 8 defines a direction Y which, together with the longitudinal direction X of channels 7, defines in turn a heat exchange layer plane (X,Y). The heat exchange layer plane (X, Y) might be, when the module is mounted on the dryer, either parallel to the horizontal plane (X", Y") defined by the dryer 1 or tilted with respect to the same. Alternatively or in addition, the heat exchange layer plane (X, Y) can be perpendicular to the stacking direction Z or form an angle with the same. Moreover, each heat exchange layer 8 can also be not planar, but for example curved, e.g., having a concavity pointing either up or down along the stacking direction. As an example, in fig. 3 a section of a header 5, 6 is represented. The header 5, 6 includes a cylindrical envelope 107 in which a plurality of holes 7a are realized, the channels 7 forming the heat exchange layer 8 being inserted therein. However different configurations are possible. The cross section of the headers 5, 6 is circular, as shown in the appended drawings, or oblong. The cross section of the header refers to the cross section of the header along a plane perpendicular to the stacking direction Z. Preferably, the oblong cross section is such that its smallest diameter, i.e., the smallest cord passing through the geometrical center of the cross section, is smaller than the width W of the layer 8. The refrigerant entering the module 10 via the inlet header 5 can come from the outlet header 6 of another module 10, from the compressor 33 or from the capillary tube/expansion valve 34. Additionally, the refrigerant exiting the outlet header 6 may be directed towards the inlet header 5 of another module 10, towards the capillary tube/expansion valve 34 or towards the compressor 33. The connection between the compressor 33, modules 1 0 and capillary tube 34 and between modules 1 0 is made via piping 35, as it can be seen in figure 2. In the following figures, the flow of the refrigerant R will be indicated with a dotted line having a pointing arrow in the direction of the flow.

Each heat exchange layer 8 includes two opposite ends 8b, 8c. In some embodiments, one end 8b is connected to the inlet header 5 and the opposite end 8c is connected to the outlet header 6. Alternatively, an additional intermediate header can be present, as detailed below. Alternatively, the ends 8b, 8c of the layer can be connected to the ends of adjacent layer(s) and only the lowermost and/or topmost layers are connected to either the inner or the outlet header.

According to a first embodiment of the module 10 of the dryer 1 of the invention depicted in figs. 4a and 4b, the inlet and outlet headers 5, 6 are mounted vertically (i.e. their axis Z is the vertical axis Z" of the dryer 1 ) on the basement 24 of the dryer 1 , parallel one to the other, and the channels 7 connecting the two headers 5, 6 are substantially straight along the longitudinal direction X. The stacking direction Z is parallel to the vertical direction Z". Channels 7 are divided in heat exchange layers 8, each of which includes a different tube defining upper and lower surfaces 9a,9b (see fig. 1 0) within which the channels 7 are realized. A plurality of heat exchange layers 8 connects the inlet 5 to the outlet header 6, all heat exchange layers having a first end 8b and a second end 8c longitudinally opposite to each other, the first end being connected to the inlet header and the second end being connected to the outer header. Heat exchange layers are stacked one on the other along the vertical direction Z. In addition, each heat exchange layer 8 has a width direction Y perpendicular to the longitudinal extension X of the channels 7. In the present embodiment, this width direction Y is parallel to the horizontal plane (X", Y") and to the air flow direction; i.e. the layer planes (X, Y) are horizontal (parallel to the horizontal plane (X", Y")). In other words, the module 10 is mounted so that the heat exchange layers 8 form parallel horizontal planes between which the process air flows. In each header 5, 6 in correspondence of each heat exchange layer's end 8b, 8c, a plurality of apertures 7a is realized, in each aperture 7a a channel 7 being inserted. The so-formed rows of apertures 7a (visible only in fig. 3) are parallel one to the other and perpendicular to the longitudinal extension Z of the header 5, 6.

The refrigerant R enters the inlet header 5 of module 10 via an inlet aperture 5in along a flow direction parallel to the longitudinal extension Z of header 5 and branches off into the various channels 7 via apertures 7a. The heat exchange layers 8 are "parallel" to each other according to the refrigerant flow direction, which means that in all layers the refrigerant flows in the same direction. In each channel 7 forming the same layer 8, the flow of the refrigerant is substantially parallel to the flow direction of the refrigerant in the other channels and has the same direction. The refrigerant then exits the module 10 via an outlet aperture 6out of outlet header 6.

The direction of flow of refrigerant R in the headers 5, 6 is substantially perpendicular to the process air flow. In addition, the flow of the refrigerant in the inlet header 5 is parallel to the flow of the refrigerant in the outlet header 6, but with opposite directions.

In a different embodiment, not depicted, the refrigerant flow in the inlet and in the outlet header can also be parallel and have the same direction.

According to another embodiment of the module 10 of the present invention, depicted in figs. 5a and 5b, the inlet and the outlet headers 5, 6 are stacked in the stacking direction Z one on top of the other. In other words, the inlet and the outlet header 5, 6 are formed by the same pipe or tube, which includes a transversal separator 17 dividing the tube in two separated portions. The module 10 of this embodiment thus includes three parallel vertical headers connected by heat exchange layers 8, but two of the headers, the inlet and the outlet headers 5, 6, are realized as a single tube divided in two. The third header 5a is an intermediate header for the refrigerant flow. The heat exchange layers 8 are parallel one to the other defining layers' plane (X, Y) parallel to the horizontal plane (X", Y"). Each layer 8 include two opposite longitudinal ends 8b, 8c, one end being connected to either the inlet or the outlet header 5, 6 and the other end being connected to the intermediate header 5a. The flow of refrigerant entering the inlet header 5 is therefore prevented by separator 17 to go from the inlet to the outlet header. The heat exchange layers 8 are thus divided in two groups: the first group G1 connects the first portion 5 (the inlet header 5) to the intermediate header 5a and the second group G2 connects the intermediate header 5a to the second portion (outlet header 6). The refrigerant R flow which enters the inlet header 5 in a vertical Z direction is distributed via apertures 7a into the first group G1 of heat exchange layers 8 and the refrigerant flows within the parallel channels in the first group G1 towards the intermediate header 5a. Therefore, the layers within the first group G1 are parallel with respect to the refrigerant flow. The refrigerant streams exit the first group G1 of heat exchange layers 8 and enter the intermediate header 5a, where they merge. From the intermediate header 5a, the refrigerant flow then enters the second group G2 of heat exchange layers 8 reaching the outlet header 6. Thus, also the heat exchange layers within the second group G2 are parallel to each other with respect to the refrigerant flow. However, the layers of the two groups G1 , G2 are in series with respect to the refrigerant flow. Indeed, the refrigerant flows in parallel in all heat exchange layers belonging to the same group, while it has to flow through the heat exchange layers of first and the second group in a given order - the layers of the two groups being thus in series.

According to an additional embodiment of the module 10 of the dryer 1 of the invention, depicted in figs. 6a and 6b, the module 10 includes only two headers 5, 6, the inlet and the outlet header. In this case, the headers are lying on the horizontal plane (X", Y") and more preferably are disposed along the air flow direction Y". In addition, not all layers are connected to both inlet and outlet headers 5, 6, on the contrary only the topmost and the lowermost layers are connected to the inlet and the outlet layer, respectively. All other layers 8 have their ends 8b, 8c connected to their adjacent layers, e.g. one end to their lower and one end to their upper layer. Thus, the various layers 8 are substantially formed by a single channels' tube bending on itself several times in order to form the stacked layers. Being the inlet and the outlet headers 5, 6 disposed within the basement 24 substantially parallel to the process air flow direction Y", also the resulting refrigerant flow within the headers is parallel to horizontal plane (X", Y"). However, the inlet and outlet headers 5,6 are located within the basement 24 at different height along the vertical direction Z", so the plurality of layers 8 all formed by the single tube are stacked one above the other in a stacking direction Z which still corresponds to the vertical direction Z". Channels layers 8 are parallel to each other and their longitudinal extension X is perpendicular to the process air flow direction Y". The single tube within which the various channels 7 are realized has a first rectilinear portion 8e defining the first channels layer connected to the inlet header 5 via one of its ends 8b, it then includes a U-shaped bend 8f and it extends for a second rectilinear portion 8g parallel to the first rectilinear portion 8e defining the second channels layer, and so on, till the last rectilinear portion 8z forming the last layer, which is connected by one of its ends 8c to the outlet header 6. In this way, a single row of apertures 7a is formed in each header 5, 6 and the flow of refrigerant in the various layers 8 can be considered in series with respect to the refrigerant flow. The flows of refrigerant within the various channels 7 forming the channels layers are parallel to each other. Additionally, the channels layer planes (X, Y) are parallel to the horizontal plane (X", Y").

The flows of the refrigerant R in the inlet and outlet headers 5, 6 are preferably parallel to each other. The two flows can have the same direction, or opposite directions.

In the depicted examples of figures 4a-4b till 6a-6b, fins 50 between the layers are not completely shown, because the focus was on the geometrical structure of the module 1 0. Fins 50 will be better described in the following.

Referring to figs. 7a and 7b, a first and a second module 10, 10' are connected to each other. The two modules 10, 10' are both according to the invention, for example according to any of the embodiments depicted in figures 4a-4b to 6a-6b. In mentioned embodiments all such modules have been indicated with the reference numeral 10 only, however in this embodiment including two modules two different reference numbers 10, 10' will be used, in particular the prime symbol is used to differentiate between one module and the other. Therefore, in the following, all elements of the first module 10 are indicated with numerals according to the examples shown in figures 4a-4b to 6a-6b, while the corresponding elements of the second module are indicated with the same reference numerals followed by a prime symbol. The first and second heat exchanger modules 10, 1 0' can for example both belong to the condenser 31 , or both to the evaporator 32, or one to the evaporator and the other one to the condenser. The two modules 10, 10' depicted in figs. 7a and 7b are both realized according to the embodiment of figs. 4a, 4b, however they can be realized according to any embodiment of the invention. In addition, the first and second modules can also be different from each other, i.e. the first and second modules can belong to two different embodiments of the invention.

Both modules 10, 10' have heat exchange layers 8, 8' which are parallel to the horizontal plane. The stacking direction Z, Z' corresponds to the vertical direction Z" and the process air flow is substantially perpendicular to the longitudinal extension X, X' of the layers 8, 8'. The refrigerant R flow enters the inlet header 5 of the first module 10, it divides itself among the plurality of channels 7, and the various streams merges, after passing through channels 7, in the outlet header 6. The refrigerant R exits the first module 10 via the outlet header 6, thus entering the inlet header 5' of the second module 10'. In the second module 10', again the refrigerant travels through the plurality of channels 7' and exits the second module via the outlet header 6'. In this case, therefore, the modules 1 0, 10' are in series with respect to the process air flow (first the process air flow traverses the first module 1 0 and then the second module 1 0') and in series with respect to the refrigerant flow (first the refrigerant traverses the first module 10 and then the second module 1 0'). Fins are not shown in the embodiment of figure 7a and 7b.

Alternatively, many other different connections between the modules 10, 10' can be realized.

With now reference to figs. 8a and 8b, two modules 10_ηι , 10'_n.i. of either the first and/or the second heat exchanger 31 ,32 of a laundry dryer not realized according to the present invention are depicted. The two modules 10_n.i., 10'_n.i. are located adjacent one to the other, and a spacing, or gap, is present between them, the spacing or gap g_n.i. being a distance present between layers of different modules. As shown, each module 10_n.i., 10'_n.i. includes, between each couple of adjacent heat exchange layers, i.e. between each couple of layers facing one the other in the same module, a plurality of fins 50_n.i., 50'_n.i. Fins are used to increase the total heat exchange surface between the refrigerant flowing in the modules and the process air flowing in the air duct 1 1 a. As shown particularly in fig. 8b, considering for each module 10_{n i.}, 10'_{n i.} a single couple of adjacent heat exchange layers, it can be seen that the different pluralities of fins 50_n.i., 50'n.i. interposed between couples of adjacent layers belonging to the same module are distinct and separated one from the other. The gap g_n.i. present between the heat exchange layers of the first module and the heat exchange layers of the second module is substantially identical to a gap present between the two different pluralities of fins 50_n.i., 50'n.i. mounted in the two different modules. In fig. 8a, the topmost layer of both modules 1 0n ,., 10'n.i. has been removed in order to better show the separated pluralities of fins 50_n.i., 50'n.i. , one plurality for each couple of two adjacent layers belonging to the same module. With now reference to figs. 9a-9c, two modules 10, 1 0', called respectively first and second modules, connected according to the inventions are depicted. The modules 10, 10' are located in the air conduit 1 1 , and more precisely in the air duct 1 1 a, and they are hit by the process air in order to exchange heat with the same. The heat is exchanged in particular with reference to the external surfaces of the heat exchange layers 9a,9b (such as those depicted in fig. 10) and to the fins connecting the adjacent layers of the modules. The process air flowing in the air conduit and hitting the modules 1 '0, 10' is preferably blown by the fan 12, which can be located within the air circuit 1 1 .

Modules 1 0, 1 0' can belong either to the first or to the second heat exchanger 32, 31 or to both of them (one module per heat exchanger). The modules 10, 10' are located in the air conduit 1 1 in such a way that they are hit by the process air in series, e.g. process air passes through first the module 1 0 and then the module 1 0'. Modules 10, 10' are both mounted on the air conduit, e.g. in the basement 24, and are located one adjacent to the other along the air conduit 1 1 and a gap g separates the layers of the two. Although in the depicted drawings the modules 10, 10' have parallel stacking directions (the stacking direction Z of module 10 is parallel to the stacking direction Z' of module 10'), in an alternative embodiment, not shown, the two stacking directions can form an angle therebetween. In the depicted embodiment, additionally, preferably the common stacking direction Z, Z' is the vertical direction Z".

Moreover, preferably, the layers' plane (X, Y) of the first module 1 0 and the layers' plane (Χ', Υ') of the second module 10' are parallel one to the other. More preferably, the layers' plane of the first module and the layers' plane of the second module are horizontal, i.e. they are parallel to the (X", Y") plane. Even more preferably, the modules are located within the air duct 1 1 a so that the air process flow hits the modules 10, 10' substantially perpendicularly to the stacking direction Z, Z'.

The two adjacent modules 10, 10' are separated by a first gap g. The first gap is present in particular between a first heat exchange layer 8 of the first module 10 and a second heat exchange layer 8' of the second module 10'. Headers 5,6, 5', 6' of the first and second module 10,10' can be in contact to each other or they can also be separated by a second gap g2, different, for example smaller, than the first gap g.

The gap g is defined as the distance in space or spacing between the first heat exchange layer 8 of the first module 1 0 and the second heat exchange layer 8' of the second module 10', more precisely the gap g is the distance present from a boundary rim 8r of the first heat exchange layer 8 of the first module 10 to a boundary rim 8r' of the second heat exchange layer 8' of the second module 1 0'. This is shown in fig. 1 1 .

The gap g can have a constant length or a different, variable, length depending on the two points in the first and second rim 8r, 8r' which are considered. As mentioned, the two modules 1 0, 10' can be parallel or not, and in this latter case the rims 8r, 8r' are also not parallel one to the other, having thus a variable distance among them. Preferably, the gap g has a constant length. In case of parallel rims 8r, 8r', as depicted in fig. 1 1 , the gap g has always a constant length. Preferably, the gap direction is parallel to the air process flow direction Y", which in turn means that it is preferably parallel to the layers' planes (X, Y) and (Χ', Υ') themselves.

According to a characteristic of the invention, the first and second modules 10, 10' share a plurality of fins 50. The plurality of fins 50 is located on the first layer 8 of the first module 10 and on the second layer 8' of the second module 10', extending through the gap g. In other words, contrary to what is depicted in figs. 8a and 8b, a single plurality of fins 50 forms a bridge between the first and the second layers 8, 8' of the first and the second modules 10, 1 0', respectively.

More preferably, in each module 10, 10' the plurality of fins 50 is in contact with two adjacent layers in the stacking direction Z, Z'. Preferably, in each module 10, 10' there is at least a couple of adjacent heat exchange layers 8couple, 8couple' (see figure 12), which is defined as two layers which are the nearest neighbors along the stacking direction Z, Z' in the same module 1 0, 10'. Between the two adjacent layers of each couple, the plurality of fins 50 is interposed and more preferably it is in contact with the facing surfaces of both layers of each couple.

The plurality of fins 50 is not only disposed on the first and second layer of the first and second module, respectively, but also it occupies the space between the first and second layers, i.e. it extends through the gap g. Thus keeping the size of the two modules 10, 10' constant, for example identical to the situation depicted in figures 8a, 8b, the modules 10, 10' of figures 9a-9c of the invention have an increased heat exchange surface.

As visible in both figures 1 1 and 12, the plurality of fins 50 have a length which is equal to the sum of the total lengths of the gap, and of the first and second layers, in other words it is equal to W + W + length of g.

The height of the plurality of fins h is preferably equal to the spacing D1 , D2 present between the two adjacent layers of the first and/or the second couple 8couple, 8couple'. More preferably, the spacing D1 between the layers of the first couple is substantially identical to the spacing D2 between the layers of the second couple, which in turn is equal to the height h of the plurality of the fins 50.

In this way, the fins 50, occupying most of the available width and height in the modules 10, 10', maximize the surface for heat exchange. As visible in figure 1 2a, which is an enlargement of fig. 12 showing the first and the second couples 8couple, 8couple' of heat exchange layers, the fins 50 include each a wall 50w which extends from the first and the second layers 8, 8' (and preferably also from the corresponding layer forming the couple with the first and the second layer). Each wall 50w defines a heat exchange surface 50s which is the surface in which heat exchange takes place (of course other surfaces in which heat exchange takes place are present in the modules). Given the available space between two adjacent layers of different modules and the total volume of the modules which remains preferably unchanged, the surface 50s is - using the above described fins' geometry - substantially the widest possible, without adding too much complexity in the fabrication of the modules, e.g. without taking into consideration very complex surfaces. Moreover, as better visible in figures 9a, 9b, fins' walls 50w defines "tunnels" t for the process air. The tunnels t substantially extend along the direction Y" of flow of the process air. In this way, the walls 50w of fins 50 channel the process air through the modules 10, 10' reducing possible vortices and turbulence. The interruption of the tunnels after a relatively short width, as in the example of figures 8a and 8b, does not allow such an efficient result. These tunnels t therefore, realized by the fins' walls 50w, improve the heat exchange between the refrigerant R and the process air reducing the turbulence of the process air.

Although in the depicted embodiments of figs. 9a-9c, 1 1 and 12 each couple of adjacent layers in the modules 10, 10' includes a plurality of fins, it is to be understood that only some of the couple(s) might include fins between the two layers forming the couple. Some couple(s) of layers in a module could be fin-free. Additionally, not all plurality of fins might extend through both modules, in some cases the fins could be confined to a single couple of adjacent layers of a single module.

Although in the drawings 3, 4a-4b, 5a-5b, 6a-6b, 7a-7b, 9a-9c, the distance among layers in the same module and the pitch of the plurality of fins appear to be constant, this is only for drawings' clarity and simplification, in any of the mentioned embodiments modules 10, 10' can be realized having a variable pitch of the plurality of fins and/or a variable distance among adjacent heat exchange layers in the same module.

In case more than two modules 10, 1 0' connected according to the invention are present within the air conduit 1 1 , as depicted for example in fig. 2, the process air flowing in the air conduit 1 1 hits the various modules one after the other. Therefore, the distribution in the space of the process air downstream the first hit module is different than the distribution of process air upstream the same module, due to the fact that the module itself, and in particular the "turbulence minimizing effect" on the process air caused by the fins has modified the process air flow. For this reason, the geometry of the module(s) downstream another module can be different than the geometry of the first hit modules. This reasoning is applicable to all modules present in a laundry dryer 1 .

Claims

1 . A laundry dryer (1 ) comprising:

a. a casing (2) supporting a drying chamber (3) for receiving a load to be dried; b. A process air conduit (1 1 ) in communication with the drying chamber (3) where a process air stream is apt to flow;

c. A heat pump (30) having a heat pump circuit in which a refrigerant (R) can flow, said heat pump circuit including a first heat exchanger (31 ) where the refrigerant is cooled off and the process air stream is heated up, and a second heat exchanger (32) where the refrigerant is heated up and the process air is cooled off; said first and/or second heat exchanger being thermally coupled to the process air conduit (1 1 ) to perform heat exchange between said refrigerant flowing in said heat pump circuit and said process air stream; said first and/or second heat exchanger (31 ;32) further comprising a first (10) and a second heat exchanger module (10'), each module (10; 10') including

^■ An inlet header (5; 5') to direct a flow of said refrigerant (R) into said module (10, 10');

^■ an outlet header (6; 6') to discharge said refrigerant (R) from said module (10, 10'); and

^■ a plurality of heat exchange layers (8; 8') fluidly connecting said inlet (5; 5') to said outlet header (6; 6') to enable said refrigerant (R) to flow from said inlet to said outlet header and/or vice versa; said layers (8; 8') being stacked one above the others in a predetermined stacking direction (Z; Z') and each layer (8; 8') including a plurality of channels (7; 7'); characterized in that said first and said second heat exchanger modules (1 0, 10') are mounted adjacent one to the other and a first heat exchange layer (8) of the first module (10) and a second heat exchange layer (8') of the second module (10) are separated by a gap (g) in a direction incident to said stacking direction (Z, Z'), said first and said second heat exchanger modules (10, 10') including a plurality of fins (50) arranged on both said first and said second heat exchange layers (8, 8') and extending through said gap (g).

2. The laundry dryer (1 ) according to claim 1 , wherein said first module (1 0) includes a third heat exchange layer (8) forming together with said first heat exchange layer a first couple (8couple) of adjacent heat exchange layers in said stacking direction and said second module (10') includes a fourth heat exchange layer (8') forming together with said second heat exchange layer a second couple of heat exchange layers (8couple') in said stacking direction, said plurality of fins (50) being arranged between the first and third layers and between the second and fourth layers of said first and of said second couple (8couple, 8couple'), respectively.

3. The laundry dryer (1 ) according to claim 2, wherein a distance (D1 ) between the first and third adjacent heat exchange layers of the first couple (8couple) and a distance (D2) between the second and fourth adjacent heat exchange layers of said second couple (8couple') are substantially identical.

4. The laundry dryer (1 ) according to claim 3, wherein said plurality of fins (50) defines a height (h) in said stacking direction, said height (h) being substantially equal to the distance (D1 ) present between the first and third heat exchange layers or to the distance (D2) present between the second and forth heat exchange layers of said first or said second couple (8couple, 8couple'), respectively.

5. The laundry dryer (1 ) according to any of the preceding claims, wherein said gap (g) is present in a direction substantially perpendicular to said stacking direction (Z, Z').

6. The laundry dryer (1 ) according to any of the preceding claims, wherein the length of said gap (g) is preferably comprised between 5 mm and 50 mm.

7. The laundry dryer (1 ) according to any of the preceding claims, wherein said first and second heat exchange layers (8, 8') have a first and a second width (W, W), respectively, a width of said plurality of fins (50) being substantially equal to the sum of said first width (W), of said second width (W) and of a length of said gap (g).

8. The laundry dryer (1 ) according to any of the preceding claims, wherein said first and said second heat exchanger modules (10, 10') are located in an air duct (1 1 a) of said air conduit (1 1 ), and said plurality of fins (50) includes a plurality of walls (50w), each defining a heat exchange wall surface (50s), extending from said first and/or second heat exchange layer (8, 8'), said plurality of walls (50w) being arranged so that a direction of flow (Y, Y') of said process air flowing in said air duct (1 1 a) is substantially parallel to said heat exchange wall surfaces (50s).

9. The laundry dryer (1 ) according to any of the preceding claims, wherein said first and second heat exchanger modules (10, 10') are located in an air duct (1 1 a) of said air conduit (1 1 ), said first and second heat exchanger modules (10, 10') and said air duct (1 1 a) being reciprocally arranged so that a direction of flow (Y, Y') of said process air flowing in said air duct (1 1 a) is substantially perpendicular to said stacking direction (Z, Z').

10. The laundry dryer (1 ) according to any of the preceding claims, wherein said first and second heat exchanger modules (10, 10') are located in an air duct (1 1 a) of said air conduit (1 1 ), said air duct (1 1 a) and said first and second heat exchanger modules (10,1 0') being reciprocally arranged so that a direction of flow (Υ,Υ') of said process air entering in said air duct (1 1 a) is substantially parallel to said heat exchange layers (8,8') of said first and second modules (10, 1 0').

1 1 . The laundry dryer (1 ) according to any of the preceding claims, wherein said first and second heat exchanger modules (10, 10') are located in an air duct (1 1 a) of said air conduit (1 1 ), said air duct (1 1 a) and said first and second heat exchanger modules (1 0,10') being reciprocally arranged so that that a direction of flow (Υ,Υ') of said process air entering in said air duct (1 1 a) is substantially parallel to said direction of said gap (g).

12. The laundry dryer (1 ) according to any of the preceding claims, including a fan (12) to circulate said process air within said air conduit (1 1 ).

13. The laundry dryer (1 ) according to any of the preceding claims, wherein in said first and second heat exchanger modules (10, 10') a first longitudinal direction (X) of the heat exchange layers (8) of said first module (10) and a second longitudinal direction (Χ') of the heat exchange layers (8') of said second module (10') are defined, and said first and second longitudinal directions (X, X') are substantially parallel to each other.

14. The laundry dryer (1 ) according to claim 1 3, wherein said first and/or second heat exchanger modules (10, 1 0') are arranged so that said first and/or second longitudinal direction (X, X') of said heat exchange layers (8, 8') is substantially perpendicular to a direction of flow (Y, Y') of said process air inside said air duct (1 1 a).

15. The laundry dryer (1 ) according to any of the preceding claims, wherein said inlet (5, 5') and outlet header (6, 6') of said first and/or second heat exchanger module (10, 10') are located one on top of the other along said stacking direction (Z, Z').