1. Field of the invention

The invention relates to an evaporator, in particular for a motor vehicle air conditioning installation.

More specifically, it relates to evaporators having two superimposed layers each comprising a plurality of circulation conduits for a refrigerating fluid.

2. Prior art

Evaporators comprise, on the one hand, a core which is generally constituted by two layers which are formed by a plurality of parallel conduits or channels for the circulation of a refrigerating fluid and, on the other hand, distribution means for the refrigerating fluid which are arranged at the two ends of the layers in order to ensure the distribution and collection of the refrigerating fluid in the different conduits of each of the layers.

The conduits are produced either from pairs of plates which are connected and which have a plurality of walls which define channels/passages for the circulation of the refrigerating fluid, or from tubes which are connected at the two ends thereof by collection boxes which allow the passage of the refrigerating fluid from one tube to another.

In the case of plate type evaporators, the internal structure of the conduits defines different zones which each form a circulation pass of the refrigerating fluid.

In the case of tube type evaporators, they are internal walls which are provided in the collection boxes which define these passes.

The distribution means (configuration of the plates or internal partitioning of the collection boxes) are therefore configured to allow a circulation of the refrigerating fluid in a plurality of passes, with reversal of the direction of flow of the refrigerating fluid from one pass to the following pass.

Conventionally, each of the two layers of these evaporators has three or four passes.

A flow of air passes through the gaps between the fluid conduits and gives off heat to the refrigerating fluid which changes from the liquid state to the gaseous state.

The air flow which is cooled in this manner can particularly be used subsequently for air conditioning the passenger compartment of a vehicle.

Evaporators having two layers with a plurality of different fluid paths so as to define in portions of each layer, and/or from one layer to the next, a pathway of the fluid according to U-shaped circuits and/or with intersecting flows (that is to say, in opposite directions) are well-known to the person skilled in the art and are widely described in the prior art.

The operation of these evaporators is satisfactory but it is necessary to further improve the heat exchange between the refrigerating fluid and the air which is intended to be cooled.

This improvement particularly involves maximising the useful surface- area for the heat exchange between the incident air and the refrigerating fluid.

In this context, each layer of the evaporator comprises in the lower portion thereof and in the upper portion thereof distribution means for the refrigerating fluid in the layers, also referred to as distributor means.

It has been observed that the zones of the evaporator located in the region of these distribution means for the refrigerating fluid are not useful for the heat exchange because it is not possible to position at that location intermediate fins which are intended in known manner to be passed through by an air flow and to promote the heat exchange between the refrigerating fluid and the air to be cooled. This consequently limits the useful surface-area for heat exchange between the refrigerating fluid and the air to be cooled.

It is further necessary to conserve good temperature homogeneity between the different regions (right/left, upper/lower) of the evaporator, which involves control of the evaporation process, in particular from the point of view of distribution of the pressure drops within the various regions of the evaporator.

One of the objects of the invention is thus to configure an evaporator having two layers, the structure of which promotes the heat exchange between the refrigerating fluid and the air to be cooled.

Another object of the invention is to provide an evaporator having two layers, the structure of which defines for the refrigerating fluid a path which optimises the different circulation passes of the refrigerating fluid relative to each other and improves the evaporation process.

3. Statement of invention

To this end, the invention proposes an evaporator, in particular for a motor vehicle air conditioning circuit, comprising a stack of planar circulation tubes for a refrigerating fluid forming two layers which extend in parallel planes and which each comprise at least three circulation passes for the refrigerating fluid, the planar tubes delimiting between them air passages so as to cool an incident air flow which flows via the passages through the successive layers of the evaporator.

According to the invention the first layer comprises a first pass which is called an inlet pass of the refrigerating fluid in the evaporator and a last pass which is called an outlet pass of the refrigerating fluid of the evaporator, the inlet and outlet passes being adjacent and the first layer being located at the side of the incident air flow to be cooled. The outlet pass of the heat exchange fluid is located at an edge of the first layer. Still according to the invention, the planar tubes forming the lateral passes of the first layer and the second layer of the evaporator, these lateral passes being located at the edges thereof, define a U-shaped circulation path of the refrigerating fluid in a direction parallel with the air flow to be cooled and orthogonal to the stacking direction of the tubes.

The use of such U-shaped planar tubes allows the refrigerant to be returned to the lower portion or the upper portion of the evaporator in accordance with the orientation of these tubes.

The U-shaped path extends in a plane parallel with the air flow to be cooled.

This allows arrangement of the intermediate fins for the heat exchange between the air and the evaporator as far as a location at the bottom or top thereof.

Thus, it is possible to reduce the non-useful surface-area portion, which is also referred to as a zone, for the heat exchange between the refrigerating fluid and the air to be cooled, and therefore to improve this heat exchange.

The use of such U-shaped planar tubes further allows a reduction of the pressure drop at the incident air flow because a portion of fin replaces a portion which beforehand did not allow the flow of the air.

The use of U-shaped planar tubes at each of the lateral passes further allows conservation of a central symmetry in the arrangement of the evaporator.

The air flows at the right and left outlets of the evaporator can thus be constantly balanced.

An evaporator according to the invention further has the advantage that the warmest passes are arranged at the side of the incident air flow and the coldest passes are arranged at the side of the outlet of the air flow of the evaporator. The passes which are passed through last by the refrigerating fluid, that is to say, the coldest passes, are therefore arranged on the second layer. This specific embodiment of the inlet and outlet passes of the evaporator allows optimisation of the homogeneity of the temperature of the cooled air at the outlet of the evaporator.

Such a configuration further allows an improvement of the heat exchanges between the evaporator and the air which passes through it because the temperature differential between the air flow passing through the evaporator and the temperature of the refrigerating fluid is maximised.

Furthermore, the fact of arranging the fluid outlet pass at an end of the first layer allows implementation of a conventional overheating phase of the refrigerating fluid so that the fluid evaporates completely before injection into the compressor of an air conditioning circuit, for example.

According to a particular aspect of the invention, the tubes of the stack are stacked alternately with fins, which are also referred to as intermediate members, which are passed through by the incident air flow to be cooled.

According to a particular aspect of the invention, each layer is constituted by a plurality of parallel conduits which are passed through by the refrigerating fluid, at least one lateral pass comprising more conduits than at least one central pass.

Unlike a lateral pass, a "central pass" is not positioned at the edge of a layer. The relative increase of the number of conduits of a lateral pass, in comparison with a central pass, allows an increase in the useful surface-area of heat exchange of the lateral pass while limiting the surface-area portions which are dedicated to the circulation of the refrigerant between the different passes.

According to a particular aspect of the invention, the fins which are arranged between the tubes of the lateral passes are longer than the fins which are arranged between the tubes of at least one central pass which is located between the lateral passes.

The relative increase of the length of the fins of a lateral pass in comparison with a central pass also allows an increase of the useful surface-area for heat exchange of the lateral pass while limiting the surface-area portions which are dedicated to the circulation of the refrigerant between the different passes.

According to a particular aspect of the invention, the evaporator comprises six circulation passes of the refrigerating fluid, the first and second layers each comprise three circulation passes of the refrigerating fluid.

According to a particular aspect of the invention, the first layer successively comprises the last outlet pass, the first pass and a second circulation pass of the refrigerating fluid.

According to a particular aspect of the invention, the second layer successively comprises a fifth circulation pass, a fourth circulation pass and a third circulation pass of the refrigerating fluid, which are arranged opposite the last outlet pass, the first pass and the second pass of the first layer, respectively.

According to a particular aspect of the invention, the U-shaped tubes of the lateral passes of a first edge of the evaporator are positioned counter to the U-shaped tubes of the lateral passes of a second edge of the evaporator.

According to a particular aspect of the invention, each layer is constituted by a plurality of parallel conduits through which the refrigerating fluid passes and which are defined by the tubes, the last pass and the fifth pass comprising between 20% and 40% of the conduits.

According to another aspect of the invention, the last pass and fifth pass comprise approximately 40% of the conduits.

The first, second, third and fourth passes therefore comprise approximately 60% of the conduits of the evaporator, that is to say, approximately 30% each.

Such a distribution of the conduits in the passes of the evaporator allows an optimum performance of the evaporator to be prioritised in terms of temperature difference between the incident air and the air being discharged from the evaporator. According to another aspect of the invention, the last and fifth passes comprise approximately 30% of the conduits.

The first, second, third and fourth passes therefore comprise approximately 70% of the conduits of the evaporator, that is to say, approximately 35% each.

Such a distribution of the conduits in the passes of the evaporator allows an optimum homogeneity of the temperature of the air being discharged from the evaporator to be prioritised.

According to an aspect of the invention, the evaporator comprises eight passes, the first and second layers each comprising four circulation passes of the refrigerating fluid.

According to an aspect of the invention, each pass of the evaporator comprises between thirty and fifty conduits, in which the refrigerant circulates.

The invention also relates to an automotive air conditioning circuit comprising at least one evaporator as described above.

4. List of Figures

Other features and advantages of such evaporators according to the invention will be appreciated more clearly from a reading of the following detailed description of two specific embodiments of the invention, which are given by way of non-limiting illustrative and simple examples, and the appended drawings, in which:

Figure 1 is a schematic top view of the configuration of the circulation passes of the refrigerating fluid in an evaporator according to a first embodiment of the invention;

Figure 2 is a perspective view of the evaporator of Figure 1 showing the direction of flow of the fluid in the passes;

Figure 3 is a schematic side view of a U-shaped plate used in an evaporator according to the invention; Figure 4 is a schematic front view of an evaporator having two layers and two passes of the prior art comprising a stack of U-shaped plates;

Figure 5 is a schematic front view of the so-called "useful" and "non-useful" front surface-areas of the evaporator according to the first embodiment of the invention;

Figure 6 is a schematic top view of the configuration of the circulation passes of the refrigerating fluid in an evaporator according to a second embodiment of the invention;

Figure 7 is a perspective view of the evaporator of Figure 3 showing the direction of flow of the fluid in the passes; and

Figure 8 illustrates the pressure and temperature variation lines of the refrigerating fluid which flows in an evaporator.

5. Detailed description of the invention

In the different Figures, unless otherwise indicated, identical elements have the same reference numerals and have the same technical features and operating modes.

The different embodiments according to the present invention are configured very particularly to optimise the pressure drops suffered by the refrigerating fluid during the different circulation passes in the evaporator, thereby leading to better control of the evaporation process and a better homogeneity of the temperature of the cooled air at the outlet of the evaporator in particular.

These different embodiments of the present invention are intended to further maximise the useful front surface-area of the evaporator for the heat exchange between the incident air and the refrigerating fluid.

The embodiments described below relate to an evaporator of the plate type which is used in a refrigerating fluid circuit for air conditioning the passenger compartment of a motor vehicle. 5.1 Description of a first embodiment

Figures 1 and 2 illustrate an evaporator 1 according to a first embodiment comprising an evaporator core 10 which is constituted by two adjacent layers 11, 12 which extend in parallel planes.

The first layer 11 of the evaporator 1 is located at the side of the inlet of the incident air flow or warm air flow 9A to be cooled while the second layer 12 is located behind the first layer 11, that is to say, at the side of the outlet of the air flow referred to as the cooled air flow 9B of the evaporator 1.

Each layer 11, 12 is formed by a plurality of parallel conduits 13 through which a refrigerating fluid passes so as to cool the air flow 9A which successively passes through the first layer 11 and second layer 12.

An inlet port 131 and an outlet port 132 for refrigerating fluid are arranged on a lateral face of the evaporator 1.

The evaporator 1 is constructed from a stack of planar tubes, each planar tube being formed by two sheet metal plates which are in contact with each other at the peripheral edges thereof so as to define with the internal walls thereof circulation conduits 13 of the refrigerating fluid.

Thus, the conduits 13 are constructed from the individual plates which are connected to each other so as to define a predetermined circulation of the refrigerating fluid.

There is left between each planar tube a space for the passage of an air flow to be cooled.

In known manner, the plates are configured so as to define fluid distributor means to at least one of the two ends (upper and/or lower end) of the layers.

These distributor means ensure the distribution and the collection of the refrigerating fluid in the different conduits 13 of the layers 11, 12, defining a circulation of the fluid between the distributor means in a given direction for each conduit 13. In the embodiment of Figure 2, the plates of the evaporator 1 have openings at the upper end, the openings being bordered by collars so as to form an inlet collection space which is connected to the inlet port 131 and an outlet collection space which is connected to the outlet port 132 when the plates are stacked.

As Figure 1 shows, the evaporator core 10 is divided into six zones or passes which are uniformly distributed here between the two layers 11, 12.

The term "circulation pass" is intended to be understood to mean the path of the refrigerating fluid in one or more conduits 13 of a layer.

In other words, the first layer 11 and the second layer 12 each comprise three passes.

Thus, the first layer 11 is divided into three zones in the direction of the length of the evaporator 1, defining from one edge to the other three circulation passes of the refrigerating fluid.

According to the invention, the first pass, referred to as the inlet pass of the refrigerating fluid, and the sixth pass 106, referred to as the outlet pass of the refrigerating fluid or last pass, of the evaporator 1 are arranged in the first layer 11 of the evaporator 1.

More specifically, an object of the invention is to provide this inlet pass 101 and outlet pass 106 in an adjacent manner and to position the outlet pass 106 of the fluid at an edge of the first layer 11 (on the left in Figure 1) and therefore near a lateral face of the evaporator.

A second pass 102 is arranged in an adjacent manner to the inlet pass 101 of the fluid, at the other edge of the first layer 11 (on the right in Figure 1).

The inlet pass 101 is therefore arranged at the centre of the first layer 11, between the outlet pass 106 and a second pass 102.

The second layer 12 is also divided into three zones in the direction of the length of the evaporator 1, defining three circulation passes of the refrigerating fluid. This second layer successively has (from right to left in Figure 1) a third pass 103, a fourth pass 104 and a fifth pass 105. The third pass 103 is located at an edge of the second layer 12 (on the right in Figure 1) and is opposite the second pass 102 of the first layer 11. The fifth pass 105 is located at the other edge of the second layer 12 (on the left in Figure 1) and is opposite the outlet pass 106 of the fluid of the first layer 11. The fourth pass 104, which is located opposite the inlet pass 101 of the fluid, is arranged at the centre of the second layer 12, between the fifth pass 105 and the third pass 103.

Therefore, the evaporator 1 comprises six successive passes 101, 102, 103, 104, 105, 106 which define a circulation circuit for the refrigerating fluid between the inlet 131 and the outlet 132 of the fluid of the evaporator 1, with a reversal of the direction of flow of the fluid in each successive pass, as illustrated in Figure 2.

More specifically, the direction of flow of the passes (the passes 103 and 105, for example) adjacent to a given pass (the pass 104) is reversed in relation to the direction of flow of the fluid of this pass (the pass 104).

For example, for the first pass 101, the circulation of the fluid is carried out downwards while for all the passes (the passes 106, 102 and 104) adjacent to this first pass 101, the circulation of the fluid is carried out upwards.

This characteristic may be applied to all the passes of the evaporator 1. This specific configuration of the passes of the evaporator 1 is found to be optimum both for maximising the temperature difference between the incident air flow 9A and the cooled air flow 9B after passing through the evaporator 1 and for conserving good temperature homogeneity between the different regions (right/left, upper/lower) of the evaporator 1.

This is because, as illustrated in Figure 8, the inventors have observed that the temperature of the refrigerating fluid decreased while it flowed in the evaporator because of the reduction in pressure (connected with the pressure drops) of the fluid between the inlet and the outlet of the fluid in the evaporator. The fluid circulation passes which are coldest are therefore those which are located last in the circulation circuit.

Furthermore, it is known to overheat the outlet pass of the refrigerating fluid (as illustrated on the right of the second line of Figure 8) so that the fluid, at the outlet of the evaporator, is only in the gaseous phase and therefore at a higher temperature, before injection into the compressor of the air conditioning circuit, for example.

Starting from these findings, the inventors have chosen to arrange the fluid outlet pass 106 which has to be overheated on the first layer 11 of the evaporator 1, this first layer 11 being in contact with the incident air flow 9A (warm air).

The first pass 101 and second pass 102 which are also the hottest ones since they are located at the start of the circulation circuit of the fluid are also arranged on the first layer 11.

The fifth pass 105 which is the coldest pass since it is located at the end of the circulation circuit of the fluid is arranged counter to the hottest pass, in this instance the last outlet pass 106, on the second layer 12 of the evaporator 1.

The third pass 103 and fourth pass 104 of the second layer 12 which are also considered to be cold passes for the same reasons as the fifth pass 105 are also arranged on the second layer 12 counter to (or opposite) the second pass 102 and first pass 101 of the first layer 11.

Therefore, the invention proposes a configuration in which the warmest passes (that is to say, the passes 101, 102 and 106) are arranged on the first layer 11 and the coldest passes (that is to say, the passes 103, 104 and 105) are arranged on the second layer 12 of the evaporator 1 so as to maximise the temperature difference between the incident air flow 9A and the cooled air flow 9B after passing through the evaporator 1.

Furthermore, this configuration of the passes in the evaporator 1 allows balancing of the temperature of the passes which are arranged opposite each other (the pass 106 with respect to the pass 105, the pass 101 with respect to the pass 104, the pass 102 with respect to the pass 103) in order to conserve good temperature homogeneity between the different regions of the evaporator 1.

The reversal of the direction of flow of the fluid between two adjacent passes (of the same layer and of two different layers) also allows homogenisation of the temperature within the evaporator 1.

Still according to the invention, the passes 102 and 103 and the passes 105 and 106 which are positioned at the edges of the evaporator 1 are formed from a plurality of planar tubes of a first type, referred to as U-shaped tubes.

The plates which form a U-shaped tube define a U-shaped circulation path of the refrigerating fluid within the tube.

Figure 3 is a front view of such a plate 2.

Such a U-shaped plate 2 is constituted by two longitudinal channels 2a and 2b which comprise at the upper end thereof an intake opening 21 and an outlet opening 23 of the refrigerating fluid, respectively, and, in the region of the lower end thereof, a return passage 22 which allows the refrigerating fluid to flow between the channels 2a and 2b of the U-shaped plate 2, in which it flows in opposite directions.

Naturally, the orientation of the U-shaped plate 2 in Figure 3 is selected in a purely illustrative manner, such a U-shaped plate 2 being able to be positioned in one direction or the other, or in other words with the return passage 22 thereof orientated downwards or upwards.

A U-shaped tube is formed here by two U-shaped plates 2 which are arranged one counter to the other, the channels 2a, 2b of the two opposing plates forming conduits 13 which each belong to a pass.

Figure 5 is a schematic front view, at the side of the second layer 12, of the evaporator 1 according to the first embodiment of the invention. As described above, the evaporator 1 comprises at each of the edges thereof a pair of passes 102 and 103 and 105 and 106 which are constituted by a plurality of parallel U-shaped tubes which connect the two layers 11 and 12 to each other.

The U-shaped tubes of these passes 102, 103, 105, 106 are obtained by assembling U-shaped plates identical to the one illustrated in Figure 3.

In the region of a first edge, the U-shaped tubes which constitute the passes 102 and 103 are arranged so that the intake and outlet openings 21, 23 thereof for the refrigerant are positioned in the lower portion of the passes and the return passage 22 thereof is positioned in the upper portion.

According to this configuration and as indicated by the direction arrows of Figure 5, the refrigerant is returned to the upper portion of the passes 102 and 103, which is included in the useful zone 3a of heat exchange between the refrigerant and the air which passes through the evaporator 1.

In the region of the opposite edge of the evaporator 1, the U-shaped tubes which constitute the passes 105 and 106 are arranged in opposite directions in relation to the passes 102 and 103 at the other edge.

Thus, the U-shaped tubes of the passes 105 and 106 are arranged so that the intake and outlet openings 21, 23 thereof for the refrigerant are positioned in the upper portion of the passes and the return passage 22 thereof is positioned in the lower portion.

According to this configuration and as indicated by the direction arrows of Figure 5, the refrigerant is returned to the lower portion of the passes 105 and 106, which is included in the useful zone 3a of heat exchange between the refrigerant and the air which passes through the evaporator 1.

Unlike the useful zones 3a of heat exchange, the surface-area portions of the evaporator 1 which are located in the region of the distribution means and collection means of the refrigerant in the passes do not allow a satisfactory heat exchange and therefore form non-useful zones 3b of heat exchange. Such a configuration of the evaporator 1 allows permanent balancing of the air flows in the region of the right and left outlets of the air conditioning circuit because of the central symmetry observed in the arrangement of the evaporator 1.

In the central passes 101, 104, the tubes are not U-shaped unlike the lateral passes and have at the upper and lower ends thereof inlet and outlet openings for the refrigerating fluid.

As illustrated in Figure 5, the non-useful zones 3b of heat exchange extend for these central passes 101, 104 at the upper and lower ends of the bundle.

Figure 4 is a schematic view of an evaporator which has two layers and two passes (that is to say, one pass per layer, the passes being in opposite directions) of the prior art and which is constituted by a stack of U-shaped plates which are identical to the one illustrated in Figure 3.

In the embodiment illustrated, the U-shaped tubes which are formed from these plates allow the refrigerant to be returned to the lower portion of the passes.

A "non-useful" surface-area portion 3b is located at the upper end of the passes in the region of the distribution and collection means of the refrigerating fluid. This surface-area portion 3b of the front surface-area of the evaporator is used for the circulation of the refrigerating fluid and is therefore not useful for the heat exchange between the air and the refrigerant, which reduces the thermal power level of the evaporator.

By way of example, the front surface-area dedicated to the circulation of refrigerating fluid is 15%.

Fins or intermediate members which extend as far as the bottom of the passes can be arranged between the U-shaped tubes in order to promote the heat exchange between the air and the refrigerant. However, these fins cannot extend into the upper portion of the passes. The surface-area portion which is covered by these fins is therefore described as a "useful surface-area portion" 3a for heat exchange between the air passing through the fins and the refrigerating fluid.

Compared with this evaporator of the prior art, the extent of the useful surface-area portion of the evaporator 1 of the first embodiment is increased by 5%.

In other words, the heat exchange surface-area between the air and the refrigerating fluid which flows in the evaporator is increased and the front surface-area which is dedicated to the circulation of the refrigerating fluid between the different passes is reduced.

In the case of a bundle having a height of 200 mm, this useful surface- area portion is increased by 6%.

The evaporator 1 has a central symmetry so that the air flows passing through the right and left portions of the evaporator are balanced.

Furthermore, the pressure drop in the region of the air flow is reduced since a portion of fin replaces a portion which did not allow the air to flow.

More generally, the front surface-area of heat exchange between the air and the refrigerant which flows in the evaporator 1 is increased in comparison with the known evaporators having two layers which allows the heat exchange to be improved.

In Figures 1 and 2, the first layer 11 and second layer 12 have identical dimensions.

The six zones which define the six passes of the evaporator 1 have such dimensions that the sixth pass 106 and fifth pass 105 together comprise between 20% and 40% of the total conduits of the evaporator 1.

More specifically, in Figure 1, the zones which define the different passes of the evaporator 1 have dimensions such that the sixth pass 106 and the fifth pass 105 together comprise approximately 40% of the total conduits of the evaporator 1, that is to say, approximately 20% each. Approximately 60% of the remaining conduits are included in the first pass 101, second pass 102, third pass 103 and fourth pass 104, that is to say, approximately 15% of the total conduits of the evaporator 1 per pass.

This distribution of the conduits 13 of the evaporator 1 in the different passes thereof allows the production of an optimum thermal performance level of the evaporator 1.

In other words, with this distribution, priority is given to the optimisation of the difference between the temperature of the incident air 9A and the temperature of the cooled air 9B which is discharged from the evaporator 1.

In a variant (not illustrated), the zones which define the different passes of the evaporator have such dimensions that the sixth and fifth passes 106, 105 together comprise approximately 30% of the total conduits of the evaporator 1, that is to say, approximately 15% each.

The first pass 101, second pass 102, third pass 103 and fourth pass 104 therefore comprise approximately 70% of the remaining conduits, that is to say, approximately 17.5% each of the total conduits of the evaporator 1.

This distribution of the conduits 13 of the evaporator 1 in the different passes thereof allows the production of an optimum compromise between the thermal performance level and the homogeneity of the temperature of the cooled air 9B being discharged from the evaporator.

It should be noted that, in this first embodiment, each pass of the evaporator 1 comprises between thirty and fifty conduits 13.

According to a particular aspect of the invention, at least one lateral pass comprises more parallel conduits than at least one central pass.

The relative increase of the number of conduits of a lateral pass in comparison with a central pass allows an increase of the useful surface-area for heat exchange of the lateral pass while limiting the surface-area portions which are dedicated to the circulation of the refrigerant between the different passes. According to another particular aspect of the invention which can be implemented alternatively or in combination, the fins of at least one lateral pass are longer than the fins of at least one central pass.

The relative increase of the length of the fins of a lateral pass, in comparison with a central pass, also allows an increase of the useful surface-area for heat exchange of the lateral pass while limiting the surface-area portions which are dedicated to the circulation of the refrigerant between the different passes.

According to a particular aspect of the invention which is not illustrated, the non-useful zones 3b for the heat exchange are covered with an anti- corrosion coating.

5.2 Description of a second embodiment

Figures 6 and 7 illustrate an evaporator 100 according to a second embodiment of the invention.

In a manner similar to the embodiment described above, the evaporator 100 comprises an evaporator core 10 which is constituted by two adjacent layers 11, 12 which extend in parallel planes.

The first layer 11 of the evaporator 1 is located at the side of the inlet of the incident air flow 9A which is intended to be cooled while the second layer 12 is located behind the first layer 11, that is to say, at the side of the outlet of the cooled air flow 9B of the evaporator 1.

Each layer 11, 12 is formed by a plurality of parallel conduits 13 through which a refrigerating fluid passes so as to cool the incident air flow 9A which successively passes through the first layer 11 and second layer 12.

As Figure 6 shows, the evaporator core 10 is divided into eight zones, or passes, which are distributed uniformly here over the two layers 11, 12. In other words, the first layer 11 and the second layer 12 each comprise four passes. The configuration of the eight passes of the evaporator 100 is substantially similar to that of the evaporator 1 described above.

This is because the evaporator 100 comprises eight successive passes 111, 112, 113, 114, 115, 116, 117, 118 which define a circulation circuit of the refrigerating fluid between the inlet 131 and the outlet 132 of the fluid of the evaporator 100 with reversal of the direction of flow of the fluid for each successive pass, as illustrated in Figure 4.

According to the invention, the inlet 131 and the outlet 132 of the refrigerating fluid are arranged in the first layer 11 of the evaporator 100.

The first layer 11 therefore comprises the first pass 111, referred to as the inlet pass of the fluid, and the eighth pass 118, referred to as the last pass or outlet pass of the fluid, of the evaporator 1.

More specifically, the invention proposes the provision of these passes 111, 118 in an adjacent manner and the placement of the last pass 118 at an edge of the first layer 11 (on the left in Figure 3).

This specific configuration of the passes of the evaporator is found to be optimum both for maximising the temperature difference between the incident air flow 9A and the cooled air flow 9B after passing through the evaporator 100 and for conserving good temperature homogeneity between the different regions (right/left, upper/lower) of the evaporator 100.

This is because the last pass 118 which has to be overheated is arranged on the first layer 11 of the evaporator 100, this layer 11 being orientated at the side of the incident air flow 9A (warm air).

The first pass 111, second pass 112 and third pass 113 which are also the warmest because they are located at the start of the circulation circuit of the fluid are also arranged on the first layer 11.

The seventh pass 117 which is the coldest pass because it is located at the end of the circulation circuit of the fluid is arranged counter to the warmest pass, that is to say, the eighth and last pass 118, on the second layer 12 of the evaporator 100.

The fourth pass 114, fifth pass 115 and sixth pass 116 which are also considered to be cold passes for the same reasons as the seventh pass 117 are also arranged on the second layer 12 counter to the third pass 113, second pass 112 and first pass 111, respectively.

Therefore, the invention proposes a configuration in which the warmest passes (the passes 111, 112, 113 and 118 in this instance) are arranged on the first layer 11 and the coldest passes (the passes 114, 115, 116 and 117 in this instance) are arranged on the second layer 12 of the evaporator 100 so as to maximise the temperature difference between the incident air flow 9A and the cooled air flow 9B after passing through the evaporator 100.

Furthermore, this configuration of the passes in the evaporator 100 allows balancing of the temperature of the passes which are arranged opposite each other (the pass 117 with respect to the pass 118, the pass 116 with respect to the pass 111, the pass 115 with respect to the pass 112 and the pass 114 with respect to the pass 113) in order to conserve good temperature homogeneity between the different regions of the evaporator 100.

In this second embodiment, the direction of flow of the passes adjacent to a given pass is also reversed in relation to the flow direction of the fluid of this pass.

For example, for the first pass 111, the circulation of the fluid is carried out downwards while for all the passes (the passes 118, 112 and 116) adjacent to this first pass 111, the circulation of the fluid is carried out upwards.

This feature can be applied to all the other passes of the evaporator 100.

The reversal of the direction of flow of the fluid between two adjacent passes also allows homogenisation of the temperature within the evaporator 100. Still according to the invention, the passes 113 and 114 and the passes 117 and 118 which are positioned at the edges of the evaporator 1 are constituted by a plurality of parallel U-shaped tubes which connect the two layers 11 and 12 to each other.

These edge or lateral passes have the same technical advantages as those set out in the context of an evaporator 10 according to the first embodiment, as described above.

The U-shaped tubes of these passes 113, 114, 117, 118 are obtained by assembling U-shaped plates which are identical to the one illustrated in Figure 3.

In the region of a first edge, the U-shaped tubes which constitute the passes 117 and 118 are arranged so that the intake and outlet openings 21, 23 thereof for the refrigerant are positioned in the upper portion of the passes and the return passage 22 is positioned in the lower portion.

In the region of a second edge, the U-shaped tubes which constitute the passes 113 and 114 are arranged so that the intake and outlet openings 21, 23 thereof for the refrigerant are positioned in the upper portion of the passes and the return passage 22 is positioned in the lower portion.

5.3 Other aspects and variants

The two embodiments described above relate to evaporators having two layers with three and four circulation passes per layer, respectively.

Naturally, it will be understood that the invention is also applied to evaporators having five, six or a greater number of passes per layer, without for all that departing from the principle of the invention.

The evaporator according to the invention may be implemented in HVAC housings (Heating, Ventilation and/or Air Conditioning) of motor vehicles.

By way of non-limiting example, the evaporator can be fixed in the container by means of a connection of the slide type, in which the upper and lower portions of the evaporator slide in corresponding grooves which are arranged in the container.