Method for determining the thermal performance of a turbomachine nacelle heat exchanger

Abstract

This method for determining the thermal performance of a heat exchanger comprising channels delimited by welded inner and outer skins and through which a fluid circulates includes: - finite element discretization of the outer skin; - determination of a temperature evolution function between the channels; - determination of an average temperature of the heat exchanger between the channels by applying a discretized integral method; - determination of a temperature of the inner skin forming an inner wall of the channels; - determination of an aerodynamic skin equation for the outer skin by applying a finite difference method; - determination of the total power dissipated by the heat exchanger; - determination of the thermal performance of the heat exchanger. Figure for the abstract: Fig 3

Description

Title of the invention: Method for determining the thermal performance of a turbomachine nacelle heat exchanger. Technical field

[0001] The invention relates technically to turbomachine nacelle heat exchangers.

[0002] In particular, the invention relates to a method for determining the thermal performance of a turbomachine nacelle heat exchanger, in particular a surface type exchanger, a computer program for implementing such a method and a computer-readable data carrier on which such a computer program is recorded. Previous techniques

[0003] An aircraft turbomachine includes heat exchangers positioned Typically located at the turbomachine nacelle, for example as described in document WO 2024 / 038230, these heat exchangers are used to cool the turbomachine lubricant. Surface heat exchangers are particularly advantageous because they do not degrade the surrounding airflow (unlike matrix heat exchangers).

[0004] In view of the technological developments of turbomachinery, in particular their hybridization, heat exchangers must cool lubricants whose temperature is increasingly higher.

[0005] In addition, these heat exchangers must not disturb the airflows of the turbomachine so as not to affect the thrust of the aircraft.

[0006] To evaluate the thermal performance of such a heat exchanger, it is possible to create prototypes and carry out experimental tests on these prototypes. This method is lengthy and expensive.

[0007] Another possibility is to numerically simulate the entire heat exchanger integrated into the turbomachine using a finite difference method, for example with commercial software. This commercial software is often complex to use and requires long computation times to simulate several heat exchangers. Description of the invention

[0008] The present invention therefore aims to overcome all or part of the aforementioned drawbacks, and to provide a simpler and faster method for setting all the characteristic dimensions of the heat exchanger.

[0009] The present invention relates to a method for determining the thermal performance of a turbomachine nacelle heat exchanger, the heat exchanger comprising an inlet distributor, an outlet manifold, and a plurality of channels, each extending between the distributor and the manifold, and each delimited by inner and outer skins of the heat exchanger welded together to form weld zones of the inner and outer skins, a heat transfer fluid circulating through the channels from the distributor to the manifold, the method being implemented by computer and comprising:

[0010] - the finite element discretization of the outer skin of the heat exchanger;

[0011] - the determination of a temperature evolution function of the heat exchanger heat between each pair of successive channels as a function of a position along a direction transverse to the channels;

[0012] - the determination of an average temperature of the heat exchanger between the two successive channels of the pair considered from the evolution function determined by applying a discretized integral method;

[0013] - the determination of a temperature of the inner skin forming a wall internal temperature of each of the two successive channels of the pair considered as a function of the determined average temperature;

[0014] - the determination of an aerodynamic skin equation for the outer skin which takes into account, in the welding zones of the inner and outer skins, a flux density coming from the inner skin forming the inner wall of each channel by applying a finite difference method;

[0015] - the determination of the total power dissipated by the heat exchanger since the heat transfer fluid to the outside air at the heat exchanger; and

[0016] - the determination of the thermal performance of the heat exchanger.

[0017] The use of an integral method to determine the average temperature of the heat exchanger between each pair of successive channels significantly reduces the time required to determine the thermal performance of the heat exchanger (e.g. a few minutes of computation time for a given exchanger configuration) compared to a known prior art method in which a finite difference method is applied to the whole heat exchanger.

[0018] The use of a finite difference method to determine the aerodynamic skin equation of the outer skin ensures high accuracy of the process, as the temperature varies rapidly along the outer skin.

[0019] The discretized integral method is used since the outer skin of the heat exchanger is already discretized into finite elements for the finite difference method.

[0020] Determining the aerodynamic skin equation by taking into account, in the weld areas, the flux density from the inner skin forming the inner wall of the channels significantly improves the accuracy of the process.

[0021] Determining the thermal performance of the heat exchanger allows the dimensional parameters of the heat exchanger to be validated or invalidated.

[0022] Chapter 4 of the English book "Fundamentals of Heat and Mass Transfer" by FP Incropera and DP De Witt describes in particular the use of a finite difference method applied to thermodynamics.

[0023] Advantageously, the outer and inner skins are welded by friction-kneading.

[0024] Advantageously, the outer and inner skins are made of the same material.

[0025] Optionally, the heat exchanger includes thermal protection disposed against the inner skin.

[0026] The thermal protection arranged against the inner skin helps to limit heat exchange between the inner air and the inner skin.

[0027] Advantageously, the thermal protection is dimensioned so that a heat flux density from the air inside the inner skin to the inner skin is less than 5% of the total thermal performance of the heat exchanger.

[0028] Thus, the inner skin can be considered as adiabatic and no heat flux density from the inner air to the inner skin can be considered.

[0029] Preferably, the method includes a preliminary step of simplifying the geometry of the heat exchanger during which all the channels of the heat exchanger are considered to be identical and straight.

[0030] Advantageously, the transverse dimension of each channel is at least 5 times smaller than the distance along the transverse direction between two successive channels, preferably at least 10 times smaller.

[0031] Such a transverse dimension, or width, of the channels allows us to consider that the temperature of the heat exchanger at the edge of the channels is equal to the temperature of the inner skin forming the inner walls of the channels.

[0032] Advantageously, determining the temperature evolution function of the heat exchanger between each pair of successive channels as a function of position along the direction transverse to the channels includes an energy balance of the conduction flux densities entering a finite element located between the two successive channels considered, the conduction flux exiting the finite element considered, and the convection flux from the finite element considered to the air outside the finite element. considered, and includes the use of a first boundary condition at the edge of one of the two successive channels of the pair considered and a second boundary condition in the middle of the distance between the two channels of the pair considered.

[0033] Optionally, the first boundary condition includes the fact that the temperature at the edge of the channel considered is equal to the temperature of the inner skin forming the inner wall of the channel considered, the temperature of the channel considered being constant over the transverse dimension of the channel considered.

[0034] Optionally, the second boundary condition includes the fact that the temperature gradient along the direction transverse to the channels is zero in the middle of the distance between the two successive channels of the pair considered.

[0035] Advantageously, the determination of the temperature evolution function of the heat exchanger between each pair of successive channels as a function of position along the transverse direction and the determination of the average temperature of the heat exchanger between the two successive channels of each pair of successive channels are carried out by considering that the heat exchanger is devoid of the inner skin.

[0036] Advantageously, the finite element discretization of the outer skin is carried out by considering at most two finite elements along the vertical direction, going from the inside to the outside, preferably by considering only one finite element along the vertical direction.

[0037] Optionally, the thickness of the inner skin is at least twice as small as the thickness of the outer skin, preferably at least three times smaller.

[0038] The thickness of the inner and outer skins is considered in the vertical direction. For such thicknesses of the inner and outer skins, heat transfer by conduction is efficient, and considering one or two finite elements in the vertical direction for the finite element discretization of the outer skin does not reduce the accuracy of the determination of the thermal performance of the heat exchanger.

[0039] Optionally, at least one of the following assumptions is made:

[0040] - the regime of the heat exchanger and of the outside and inside air to the exchanger Heat is stationary. By considering a stationary regime, that is to say a permanent regime, we simplify the equations by considering the time variations as zero.

[0041] - the convection flux densities between the heat transfer fluid and the heat exchanger The heat fluxes are equal to the conduction flux densities within the heat exchanger and the convection flux densities between the heat exchanger and the outside and inside air. Therefore, no energy storage is considered, meaning there is no heating of the inner surfaces. and external over time, their temperature therefore being locally constant over time.

[0042] - the flux densities entering the heat exchanger are equal to the densities of outgoing flow from the heat exchanger. Thus, it is assumed that there is no energy storage, energy transformation, or energy creation.

[0043] - the thicknesses of the inner and outer skins of the heat exchanger are less than two millimeters, and in particular less than one millimeter. Thus, only evolutions along the direction transverse to the channels are considered. For such skin thicknesses, considering one or two finite elements along the vertical direction for the finite element discretization of the outer skin does not reduce the accuracy of determining the thermal performance of the heat exchanger.

[0044] - the heat exchanger is considered to be devoid of the inner skin for the determination of the temperature evolution function of the heat exchanger between each pair of successive channels as a function of position along the transverse direction to the channels; and - the physical properties of each material of the heat exchanger, and / or of the heat transfer fluid, in particular density, heat capacity and viscosity, are solely a function of temperature.

[0045] Optionally, one can consider a regime of the heat exchanger and of the outside and inside air to the heat exchanger which is unsteady.

[0046] The present invention also relates to a method for determining the thermal performance of a heat exchanger and for manufacturing said heat exchanger, comprising the implementation of a method for determining the thermal performance of a heat exchanger as defined above, and a manufacturing step for said heat exchanger following a step for validating the thermal performance of said heat exchanger.

[0047] The present invention also relates to a computer program comprising code instructions which, when the program is executed by a computer, lead the latter to implement a method for determining the thermal performance of a heat exchanger as defined above.

[0048] This computer program makes it possible to determine very quickly the thermal performance of a nacelle heat exchanger. Combining integral calculus with finite difference calculus, the approach is not limited by the dimensions of the channels, nor by changes in the shape of the distributor or the collector.

[0049] The present invention also relates to a computer-readable data carrier on which a computer program as defined above is recorded. Brief description of the drawings

[0050] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0051] [Fig-1] schematically illustrates a heat exchanger from below according to an example embodiment;

[0052] [Fig.2] schematically illustrates a cross-section of a semi-circular channel of the heat exchanger of [Fig.1];

[0053] [Fig.3] schematically illustrates a method for determining the thermal performance of the heat exchanger according to an embodiment of the invention;

[0054] [Fig.4] is a simplified schematic representation of the heat exchanger of [Fig.1];

[0055] [Fig.5] illustrates an energy balance of a finite element of the heat exchanger of [Fig.1] which is located between two successive channels;

[0056] [Fig. 6] illustrates an energy balance of a finite element located in the heat exchanger of [Fig. 1] which is situated at the weld between the inner and outer skins of the exchanger; and

[0057] [Fig.7] schematically illustrates a computer-readable data carrier according to an example of an embodiment of the invention. Detailed description

[0058] Fig. 1 represents a turbomachine nacelle heat exchanger 2 comprising a distributor 4, a manifold 6, and a plurality of channels 8 which each extend between the distributor 4 and the manifold 6. A heat transfer fluid, for example oil, flows in each of the channels 8 from the distributor 4 to the manifold 6.

[0059] As more visibly represented in [Fig.2], the heat exchanger 2 comprises inner skins 10 and outer skins 12, for example respectively hydrodynamic and aerodynamic skins, which are welded together, in particular by friction mixing.

[0060] The inner and outer skins 10, 12 delimit between each other the channels 8 of the heat exchanger 2.

[0061] The heat exchanger 2 further includes a thermal protection (not shown) disposed against the inner skin 10 so as to consider this inner skin 10 as adiabatic.

[0062] The longitudinal direction L is that of elongation of the channels 8. The vertical direction V is directed from the inner skin 10 to the outer skin 12. The direction transverse T is orthogonal and forms a frame of reference orthogonal with the longitudinal L and vertical V directions.

[0063] Fig. 3 represents the different stages of a computer-implemented process for determining the thermal performance of the heat exchanger 2.

[0064] Thermal performance, in the context of this description, means the capacity of the heat exchanger to dissipate thermal energy, relative to an expected capacity, corresponding to thermal design criteria of the exchanger.

[0065] Preferably, a preliminary step S0 is carried out to simplify the geometry of the heat exchanger 2 by considering that all the channels 8 of the heat exchanger 2 are identical and straight.

[0066] For example, all channels 8 are considered to be rectangular. Alternatively, all channels 8 could be considered to be semi-circular.

[0067] The heat exchanger 2 therefore comprises, with reference to Figure 4, inter-channel zones 16, or fins, located between two successive channels 8, channel zones 18 located outside the channels 8, and weld zones 20 of the inner and outer skins 10, 12. The inter-channel zones 16 are in particular located between two successive weld zones 20. Sections 22 of the outer skin 12 form outer parts of the channels 8. Sections 24 of the inner skin 10 form inner parts of the channels 8. The weld zones 20 form lateral, or transverse, parts 26 of the channels 8. The transverse dimension, or width, of the channels 8 is here at least 5 times smaller than the inter-channel distance dic taken along the transverse direction, and more precisely at least 10 times smaller.

[0068] Next, a discretization SI step of the outer skin 12 of the heat exchanger 2 is carried out using finite elements.

[0069] We then carry out a step S2 of determining a function of evolution of the temperature of the heat exchanger 2 between each pair of successive channels 8, i.e. in the inter-channel zones 16, as a function of a position along the transverse direction T to the channels 8.

[0070] For example, with reference to [Fig.5], an energy balance is carried out on the incoming and outgoing flux densities in a finite element located between two successive channels 8, the dimension along the longitudinal direction L of the finite element considered i being dl, the dimension along the transverse direction T of the finite element considered i being dx, the thickness of the finite element considered i being e.

[0071] The heat exchanger 2 can be considered to be without the inner skin 10. In this case, the thickness e can be considered to be equal to the thickness of the outer skin 12. Alternatively, the thickness e could be considered to include the thickness of the inner skin 10 and the thickness of the outer skin 12.

[0072] This classic energy balance is:

[0073] q'j^.e.dl=q'^x + dx) e dl + ha - (T(x) - Ta) dx dl

[0074] With '< ( v \ _ a 2L22 the conduction flux entering the considered finite element qx\X)--K- dx i, 2 the thermal conductivity of the material of the inner and outer skins 10, 12, 0 the partial derivative operator, T(x) the temperature of the finite element considered i at a position x along the transverse direction T corresponding to the entrance edge of the finite element considered i, q'^x + dx) the conduction flux out of the finite element considered i, dx the infinitesimal dimension along the transverse direction T of the finite element considered i, ha the convective heat transfer coefficient between the heat exchanger 2 and the air, and Ta the temperature of the air outside the finite elements at a distance much greater than the boundary layer of the finite element considered i.

[0075] And by setting t(x) — T(x) — Ta and m2 — we obtain: m fe 100761

[0077] This allows us to obtain the temperature evolution function of the heat exchanger 2 between each pair of successive channels 8 of the following form:

[0078] T (x) = Ta + • emx+A2 • e^x

[0079] A first boundary condition is then used at the edge of one of the two successive channels 8 of the pair considered and a second boundary condition at the midpoint of the distance between the two channels 8 of the pair considered in order to determine the coefficients A, and A2.

[0080] In particular, the first limit condition is that the temperature at the edge of the channel 8 considered, i.e. at the point M of temperature Tpm which is located at the lateral edge 26 of the channel 8 considered and to which the origin of the axis of the transverse direction T is placed, is equal to the temperature of the inner skin 10 forming the inner wall of the channel 8 considered Tpc*, i.e. at the sections 24, the temperature of the channel 8 considered being constant over the transverse dimension, or width, of the channel 8 considered.

[0081] T(x = 0) - Tpm = Tp^f

[0082] In particular, the second boundary condition is that the temperature gradient along the transverse direction T is zero in the middle of the inter-channel distance dic between the two successive channels 8 of the pair considered. 100831 Bl <=<'

[0084] Which allows us to obtain Ai = t • A > et , _ TPm Ta. " A1 ~ Mb

[0085] With a = and =

[0086] A determination step S3 of the average temperature Tn *IC of the heat exchanger 2 between the two successive channels 8 of the pair considered is then carried out by applying a discretized integral method on the n finite elements constituting the heat exchanger 2 between the two successive channels 8 considered: [00871 r^=Æ",r( âx ( )=^+(¾.^) 4E" [A

[0088] Axf is the dimension along the transverse direction T of the finite element considered i, dx being the infinitesimal dimension along the transverse direction T of this finite element considered i. This calculation allows access to the local flux density coming from the inner skin 10.

[0089] Which gives:

[0090] ^=7^...(¾¾)

[0091] With kic an integral coefficient of the fin, i.e. of the heat exchanger heat 2 between the two successive channels 8 of the pair considered.

[0092] Next, a step S4 is performed to determine the temperature Tpc* of the inner skin 10 forming the inner wall of each of the two successive channels 8 of the pair considered. For this, a macro-energy balance of the channel 8 considered is performed:

[0093] hf (Tf- T ) • Sc« -ha- (Tpm - T■ SM + (Pailette

[0094] With hf the convective heat transfer coefficient between the heat transfer fluid and the heat exchanger 2, Tf the temperature of the heat transfer fluid, μ the heat exchange surface area between the inner skin 10 and the channel 8 considered, SM the heat exchange surface area between the inner and outer skins 10, 12 welded and the channel 8 considered, and ms the heat flux density 7 fin \ ric u / le exchanged between the heat exchange surface between the two successive channels 8 of the pair considered and the air outside the outer skin 12, being the heat exchange surface between the two successive channels 8 of the pair considered and the air outside the outer skin 12.

[0095] Which ultimately allows us to obtain:

[0096] T * _ PC~ UK^

[0097] With + . kPd ~ ha{SM+k^

[0098] We then carry out a step S5 of determining an aerodynamic skin equation of the outer skin 12.

[0099] For this, a flux density balance applied to a finite element is considered between the successive channels 8 of the heat exchanger 2.

[0100] The conduction flux density entering the considered finite element i is:

[0101] W)

[0102] With €i the thickness of the finite element considered i. We can consider that the heat exchanger 2 is devoid of the inner skin 10. In this case, we can consider that the thickness ei is equal to the thickness of the outer skin 12. Alternatively, we could consider that the thickness ei includes the thickness of the inner skin 10 and the thickness of the outer skin 12.

[0103] The conduction flux density exiting the considered finite element i is:

[0104] atT^x+clx^ 'A' ei

[0105] With dxL the dimension along the transverse direction T of the finite element considered i, the dimension dx{ being able to be different from one finite element considered to another.

[0106] The convection flux density exiting the considered finite element i towards the air outside the considered finite element i is:

[0107] hui-(TrTai)-dXi

[0108] With h(d the convective heat transfer coefficient from the outside air to the finite element considered i, T; the temperature of the outer skin 12 at the center of the finite element considered i, Tai the local temperature of the outside air to the finite element considered i.

[0109] After setting up the one-dimensional differential equation, along the transverse direction T, for heat transfer, we finally obtain the following for the outer skin 12 between the successive channels 8:

[0110] -lei + h^dxi] -ei]-Ti+l = h^-dxi-Tai

[0111] With TiA the temperature of the outer skin 12 at the center of the finite element preceding the finite element considered i and TM the temperature of the outer skin 12 at the center of the finite element following the finite element considered i.

[0112] Of course, before the first channel 8 of the heat exchanger 2, no flux density entering the finite element concerned is considered. Similarly, after the last channel 8 of the heat exchanger 2, no flux density leaving the finite element concerned is considered.

[0113] Regarding the skin equation of the outer skin 12 forming an outer wall of each of the channels 8, i.e. the sections 22, the flux density from the heat transfer fluid is also taken into account:

[0114] hfrdxL

[0115] With Tfj the temperature of the heat transfer fluid at the level of the finite element considered i and with hf, the heat transfer coefficient by convection between the heat transfer fluid and the finite element considered i. It can be assumed, in particular in the regime

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127] permanent, than TTf. Similarly, we can assume that hff — hf in each channel 8. After setting up the one-dimensional differential equation for heat transfer, we finally obtain the following for the outer skin 12 forming the channels 8: -Ti-t+[lh-^+(^ + ^:) dxi] T,+ [-^ ■ei]-TM = {hf.-Tfi + hui-T^-dxi Concerning the skin equation of the outer skin 12 in the weld zones 20 of the inner and outer skins 10, 12, with reference to figure 6, we also take into account a flux density 28 which comes from the inner skin 10 forming the inner wall of each channel 8 and which is directly related to the temperature of the inner skin 10 forming the inner wall of the channel 8 considered Tpc*. After setting up the one-dimensional differential equation for heat transfer along the transverse direction T, we finally obtain the following for the outer skin 12 welded to the inner skin 10: [ - À • «] • -4' 1+e / / di33) + V • Af+ri] • • « / ] • 7« = *.< ' dxi2 ■ 7'„- + hf. ht ■ T f + phi With , Tpc , j. , the 'argcur of a finite element of the skin phi ““ J^r ' eh dxj outer 12 outside the weld zones 20, d^ the width of a finite element of a section 22 of the outer skin 12 forming an outer part of a channel 8, dxi3 the width of a finite element of the outer skin in a weld zone 20, and dxj the width of a finite element of the inner skin 10. We can consider that d^ — dxi2 = dxi3 ~ dxj- We consider here that e is the thickness of the outer skin 12, that eh is the thickness of the inner skin 10, that phi is an elementary flux coming from the sections 24 of the inner skin 10 forming inner parts of the channels 8, and that ri is a coefficient induced by the numerical decomposition. Next, we carry out step S6 to determine the total power dissipated by the heat exchanger 2. For this, we consider the total exchanged flow: = T ' EX ' ' dxi ï Finally, we carry out step S7 to determine the thermal performance of heat exchanger 2. Following an S8 step of validation of the thermal performance of the heat exchanger 2, in particular when the thermal performance meets thermal design criteria, a final manufacturing step of the heat exchanger 2 is carried out. Figure 7 schematically represents a computer-readable data storage medium 30 on which is recorded a computer program 32 comprising code instructions which, when the computer program 32 is executed by a computer, lead it to implement the process of determining the thermal performance of a heat exchanger 2 described previously.

Claims

Demands

1. Method for determining the thermal performance of a turbomachine nacelle heat exchanger (2), the heat exchanger (2) comprising an inlet distributor (4), an outlet manifold (6), and a plurality of channels (8) each extending between the distributor (4) and the manifold (6), and each delimited by inner and outer skins (10, 12) of the heat exchanger (2) welded together so as to form weld zones (20) of the inner and outer skins (10, 12), a heat transfer fluid circulating through the channels (8) from the distributor (4) to the manifold (6), the method being implemented by computer and being characterized in that it comprises: - the finite element discretization of the outer skin (12) of the heat exchanger (2);- the determination of a temperature evolution function of the heat exchanger (2) between each pair of successive channels (8) as a function of a position along a direction transverse (T) to the channels (8); - the determination of an average temperature of the heat exchanger (2) between the two successive channels (8) of the pair considered from the evolution function determined by applying a discretized integral method; - the determination of a temperature of the inner skin (10) forming an inner wall of each of the two successive channels (8) of the pair considered as a function of the determined average temperature; - the determination of an aerodynamic skin equation of the outer skin (12) which takes into account, in the weld zones (20) of the inner and outer skins (10, 12), a flux density coming from the inner skin (10) forming the inner wall of each channel (8) by applying a finite difference method;- the determination of the total power dissipated by the heat exchanger (2) from the heat transfer fluid to the outside air of the heat exchanger (2); and - the determination of the thermal performance of the heat exchanger (2).

2. A method according to claim 1, comprising a preliminary step of simplifying the geometry of the heat exchanger (2) during which all the channels (8) of the heat exchanger (2) are considered to be identical and straight.

3. A method according to claim 1 or 2, wherein the transverse dimension of each channel (8) is at least 5 times smaller than the distance along the transverse direction between two successive channels (8), preferably at least 10 times smaller.

4. A method according to any one of claims 1 to 3, wherein the determination of the temperature evolution function of the heat exchanger (2) between each pair of successive channels (8) as a function of position along the transverse direction (T) to the channels (8) comprises an energy balance of the conduction flux densities entering a finite element located between the two successive channels (8) considered, of conduction flux exiting the finite element considered, and of convection flux from the finite element considered to the air outside the finite element considered, and comprises the use of a first boundary condition at the edge of one of the two successive channels (8) of the pair considered and a second boundary condition at the midpoint of the distance between the two channels (8) of the pair considered.

5. A method according to claim 4, wherein the first boundary condition comprises the fact that the temperature at the edge of the channel (8) considered is equal to the temperature of the inner skin (10) forming the inner wall of the channel (8) considered, the temperature of the channel (8) considered being constant over the transverse dimension of the channel (8) considered, and / or wherein the second boundary condition comprises the fact that the temperature gradient along the transverse direction (T) to the channels (8) is zero at the midpoint of the distance between the two successive channels (8) of the pair considered.

6. A method according to any one of claims 1 to 5, wherein the determination of the temperature evolution function of the heat exchanger (2) between each pair of successive channels (8) as a function of position along the transverse direction (T) and the determination of the average temperature of the heat exchanger (2) between the two successive channels (8) of each pair of successive channels (8) are carried out considering that the heat exchanger (2) is devoid of the inner skin (10).

7. A method according to any one of claims 1 to 6, wherein at least one of the following assumptions is made: - the regime of the heat exchanger (2) and of the air outside and inside the heat exchanger is steady; - the convection flux densities between the heat transfer fluid and the heat exchanger (2) are equal to the conduction flux densities within the heat exchanger (2) and to the convection flux densities between the heat exchanger (2) and the air outside the heat exchanger (2); - the flux densities entering the heat exchanger (2) are equal to the flux densities leaving the heat exchanger (2); - the thicknesses of the inner and outer skins (10, 12) of the heat exchanger (2) are considered to be less than two millimeters, in particular less than one millimeter;- it is assumed that the heat exchanger (2) is without the inner skin (10) for the determination of the temperature evolution function of the heat exchanger (2) between each pair of successive channels (8) as a function of position along the transverse direction (T) to the channels (8); and - the physical properties of each material of the heat exchanger (2), and / or of the heat transfer fluid, in particular density, heat capacity and viscosity, are solely a function of temperature.

8. Method for determining the thermal performance of a heat exchanger (2) and for manufacturing said heat exchanger (2), comprising implementing a method for determining the thermal performance of a heat exchanger (2) according to any one of claims 1 to 7, and a step of manufacturing said heat exchanger (2) following a step of validating the thermal performance of said heat exchanger (2).

9. Computer program (32) comprising code instructions which, when the program is executed by a computer, cause the computer to implement a method for determining the thermal performance of a heat exchanger (2) according to any one of claims 1 to 7.

10. Computer-readable data carrier (30) on which a computer program (32) according to claim 9 is recorded.

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