Method for manufacturing an interlayer element for a heat exchanger

Abstract

Title of the invention: Method for manufacturing an interlayer element for a heat exchanger. Method for manufacturing an interlayer element for a plate and fin type heat exchanger, said method comprising the following steps: a) applying a surface texture to at least a portion of the surface of a sheet (1), b) obtaining a corrugated structure (2) by deforming said sheet, said corrugated structure comprising a series of fins (11) connected to each other alternately by wave crests (10) and wave bases (12), characterized in that steps a) and b) are carried out simultaneously using the same forming tool (3, 4). Abstract figure: Fig. 2

Description

Title of the invention: Method for manufacturing an interlayer element for a heat exchanger

[0001] The present invention relates to a method for manufacturing an intercalated element for a plate and fin type heat exchanger.

[0002] The present invention finds particular application in the field of cryogenic gas separation, especially cryogenic air separation (known by the English acronym "ASU" for air separation unit) used for the production of pressurized gaseous oxygen. In particular, the present invention can be applied to a heat exchanger that vaporizes a liquid flow, for example liquid oxygen, nitrogen, and / or argon, by exchanging heat with a heat-generating gas, for example air or nitrogen.

[0003] If the heat exchanger is located in the tank of a distillation column, it can constitute a thermosiphon vaporizer in which the exchanger is immersed in a bath of liquid descending the column or a film vaporizer fed directly by the liquid falling from the column and / or by a recirculation pump.

[0004] The present invention can also be applied to a heat exchanger which vaporizes at least one flow of liquid-gas mixture, in particular a flow of mixture of several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one other fluid, for example natural gas.

[0005] The present invention can also be applied to a heat exchanger contained in a cryogenic carbon monoxide purification unit.

[0006] The present invention can also be applied to a heat exchanger used for the liquefaction of hydrogen.

[0007] The technology commonly used for an exchanger is that of brazed plate and fin or wave aluminium exchangers, which make it possible to obtain very compact devices offering a large exchange surface.

[0008] These exchangers include separating plates between which are inserted heat exchange structures, generally intercalated elements of corrugated shapes also called waves, formed of a succession of fins or wave legs, thus constituting a stack of passages for the different fluids to be put into heat exchange relationship.

[0009] The role of the intercalated elements is to increase the contact surface area between the fluids and the walls of the heat exchanger in order to promote heat exchange. The performance of a heat exchanger is linked to the heat transfer coefficient of the Heat exchange structures in contact with fluids. The heat exchange coefficient of a structure depends in particular on the geometry of the structure, the nature of the material constituting it, the porosity of this material, its roughness and the flow regime of the fluids.

[0010] The improvement of the thermal performance of a heat exchanger with constant volume and temperature difference can be achieved in particular by increasing the exchange surface area and / or by increasing the heat transfer coefficient.

[0011] The increase in the heat exchange surface area is generally related to the density of the corrugated interlayer element used, usually expressed in terms of the number of fins per unit length. However, the possibility of increasing the surface area is limited since the higher the fin density, the greater the resulting pressure drop. Therefore, a compromise exists that allows the heat exchange surface area to be increased without generating an excessive pressure drop. In particular, in the case of vaporizer-condenser type heat exchangers, the increase in the heat exchange surface area is limited by the maximum wave density that can be used in the vaporization passages. Indeed, for safety reasons related to oxygen vaporization and the risks of impurity deposits and channel clogging, it is recommended to use straight, unobstructed waves while respecting a minimum channel width.

[0012] Regarding the increase in the heat transfer coefficient, this can be achieved by modifying the physicochemical properties of the heat transfer surfaces. This makes it possible to increase the effective heat transfer surface area and / or modify the interactions between the fluid and the surface, by changing properties of the surface in question, such as its wettability or its ability to intensify the boiling of a fluid. This is referred to as texturizing the heat transfer surfaces or intensified surfaces.

[0013] For example, surface texturing can be achieved by depositing porous coatings or by forming reliefs on the surface of the intercalated elements, in particular by mechanical treatments or by chemical attack.

[0014] A problem that arises with the implementation of textured surfaces in brazed aluminium heat exchangers concerns the realization of the surface textures themselves.

[0015] Indeed, due to their small size, it is difficult to access the channels formed by the undulating structures of the intercalated elements. The intercalated elements are generally straight waves and have vertical and horizontal surfaces on which it is difficult to achieve homogeneous surface texturing in terms of thickness and porosity and / or reproducibility of reliefs. Moreover, these access difficulties make the texturing operations more complex and longer, several coating passes may be required, which leads to an additional manufacturing cost.

[0016] It then becomes difficult, if not impossible, to use mechanical texturing techniques or thermal spray coating deposition. Other surface treatment techniques exist but are difficult to implement. For example, for techniques involving preliminary heat treatment steps or the application of an impregnating layer to ensure coating adhesion, the entire heat exchanger must be treated. This carries risks of clogging channels, debonding parts of the heat exchanger, creating brittle metallurgical phases, and damaging the brazed matrix.

[0017] As an alternative, it has been proposed to apply surface textures to the separator plates before brazing. However, in this case, there is no brazed interlayer to the plates, and annealing of the plates is necessary. The interlayers also act as spacers. They contribute to the rigidity of the heat exchanger passages and their compressive strength during vacuum brazing. Furthermore, the annealed plates lose some of their mechanical strength. It is therefore necessary to add extra reinforcing bars to the passages and double the plate thickness.

[0018] It has also been proposed to apply surface textures to a flat sheet before it is formed into corrugations. In this configuration, forming the sheet by bending the material is difficult to achieve without damaging the surface texture. Indeed, bending a flat sheet is an operation that violently compresses the flat sheet with a rectangular tool in a groove of complementary shape. In the case of a texture obtained by depositing porous material, material detachment can therefore occur and damage the bending mechanism itself.

[0019] Another solution is to perform surface texturing after brazing the heat exchanger, but in this case, mechanical or spray-applied texturing is not possible. And if the texturing is performed using another coating technique, subsequent heat treatment may be necessary to ensure coating adhesion. This heat treatment must then be carried out on the entire heat exchanger, at the risk of debonding parts of the exchanger or creating brittle metallic phases within these parts.

[0020] When it is desired to improve the thermal efficiency of an exchanger, it is therefore necessary to consider not only the performance in operation of the exchanger but also its method of manufacture.

[0021] The present invention aims to solve, in whole or in part, the problems mentioned above, in particular by proposing a simpler manufacturing process of an interlayer element for a plate and fin type heat exchanger with surface texture.

[0022] The solution according to the invention is then a method for manufacturing an intercalated element for a plate and fin type heat exchanger, said method comprising the following steps:

[0023] a) applying a surface texture to at least one surface of a sheet metal,

[0024] b) obtaining a corrugated structure by deformation of said sheet metal, said structure undulating, comprising a series of fins connected to each other alternately by wave bases and wave crests,

[0025] characterized in that steps a) and b) are carried out simultaneously using the same forming tool.

[0026] The present invention will now be better understood from the following description, given solely by way of non-limiting example and with reference to the attached diagram:

[0027] [Fig-1] The [Fig. 1] is a partial view of an exchanger passage comprising intercalated elements manufactured by a process according to the invention.

[0028] [Fig.2] The [Fig.2] is a cross-sectional view of a corrugated structure obtained according to an embodiment of the invention.

[0029] [Fig.3] The [Fig.3] is another cross-sectional view of a corrugated structure obtained according to an embodiment of the invention.

[0030] [Fig.4] The [Fig.4] is another cross-sectional view of a corrugated structure obtained according to an embodiment of the invention.

[0031] [Fig.5] The [Fig.5] is another cross-sectional view of a corrugated structure obtained according to an embodiment of the invention.

[0032] As can be seen in [Fig. 1], within a passage of the interchange 20, corrugated structures 11 can be superimposed. These corrugated structures 11 comprise wave crests and wave bases 10, 12 of two different types: planar and textured, in particular grooved, or non-planar.

[0033] Within the framework of the invention, surface texturing can result from a surface coating deposited on the element or from a modification of the surface condition of said element.

[0034] In particular, surface texturing can result from a surface coating deposited on the intercalated element, in particular a coating deposited by liquid means, in particular by dipping, spraying or by electrolytic means, by dry means, in particular by chemical vapor deposition (CVD) or physical vapor deposition (CVD), or by thermal projection, in particular by flame or plasma.

[0035] The modification of the surface condition of said parts may be obtained by chemical treatment or by mechanical treatment, for example by sandblasting, grooving....

[0036] According to a preferred embodiment, the surface texture is in the form of a porous material. The porous material can, for example, be formed from a deposit of slightly sintered aluminum particles, entangled aluminum filaments, or semi-molten aluminum particles bonded to one another, such as the aluminum particles obtained after projection by thermal spraying with a flame or plasma.

[0037] Preferably, the surface texture has an open porosity of between 15 and 60%, preferably between 20 and 45%, and preferably again between 25 and 35% (by volume). It should be noted that open porosity is defined as the ratio between the volume of the open pores, i.e., the pores communicating fluidly with the external environment in which the intercalated element is located, and the total volume of the porous structure.

[0038] Alternatively, the surface texture may take the form of reliefs or patterns imprinted or created in or on the material constituting the substrate of an interlayer element. Preferably, these reliefs define, in cross-section, cavities open on the surface of the element. For example, micro-reliefs of various sizes or morphologies, such as discrete or continuous grooves, striations, protrusions, etc., may be formed or deposited on the surface of the element in question. In particular, the reliefs forming the surface texture may be created by laser or mechanical and / or chemical machining.

[0039] The interlayer element manufactured according to the invention may have a height, measured orthogonally to the wave crests or bases, of between 3 and 10 mm. The crests, wave bases, and fins may have a thickness of between 0.1 and 0.6 mm. The crests and wave bases may have a width of between 2 and 10 mm.

[0040] Preferably, the interlayer element manufactured according to the invention has a wave density, defined as the number of fins per unit length measured along the direction of undulation, of between 5 and 35 fins per 2.54 centimeters (unit equivalent to the designation "fins per inch" in English or "FPI").

[0041] Preferably, the interlayer element manufactured by the process according to the invention is a straight wave having a single series of flat-surfaced fins, each fin forming a band extending across the entire width or length of the passage. The use of straight waves simplifies the manufacture of the interlayer element and is particularly advantageous in heat exchanger passages designed for the flow and vaporization of oxygen because their geometry limits the risk of impurity deposits. and channel blockage. The wave crests and bases are planar and extend parallel to each other and perpendicular to the fins. The channels formed between two successive fins and a crest or base arranged between said successive fins thus have cross-sections that are generally square or rectangular in shape.

[0042] As shown in Figures 2 to 5, a sheet 1 is fed in the direction DI into a forming tool comprising an upper jaw 3 and a lower jaw 4, said jaws having complementary shapes. A corrugated structure 2 is obtained at the exit of the forming tool. Said corrugated structure comprises a series of fins 11 connected to each other alternately by wave crests 10 and wave bases 12.

[0043] The texturing of the sheet metal can be achieved by mechanical action of the forming tool, for example by stamping, grooving, embossing, deep drawing or rolling or deposition of material.

[0044] The sheet thickness can be increased after texturing. The spacing between the jaws of the forming tool can be adjusted relative to a sheet without texturing. Furthermore, it is possible to maintain the texturing on the wave crests and ridges by also adjusting the spacing between the jaws and the spacers at the end of the tool's stroke. This spacing can be between 0.02 mm and 0.1 mm. Conversely, it is possible to reduce or eliminate the texturing on the wave crests and ridges for a spacing between 0 and 0.05 mm.

[0045] Preferably, the ratio between the height and width of the wave vertices or bases is between 1 and 2. In the case of a texture comprising grooves, the ratio between the pitch of the grooves and the thickness of each groove is preferably between 1 and 4. The pitch is the distance between each groove while said thickness of the groove itself.

[0046] The advantage of creating a textured wave is twofold. A textured wave increases the wave's exchange surface area and therefore the performance of the heat exchanger. A textured wave also improves the local heat transfer coefficient due to the impact of the liquid film thickness in the case of vaporization or condensation, or due to the local turbulence generated.

[0047] Preferably, geometric dimensions that improve the condensation or vaporization of fluids will be applied to the grooves. These geometric dimensions are crest heights between 0.05 mm and 0.4 mm, groove pitches between 0.3 mm and 1 mm, and crest thicknesses between 0.1 and 0.4 mm.

[0048] The proposed solutions of textured corrugated structures can be integrated into exchange passages where the configuration is of a single corrugated structure per passage or into exchange passages where the configuration is of several superimposed corrugated structures.

Claims

[Claim 1] Demands A method for manufacturing an interlayer element for a plate and fin type heat exchanger, said method comprising the following steps: - a) application of a surface texture on at least part of the surface of a sheet (1), - b) obtaining a corrugated structure (2) by deformation of said sheet (1), said corrugated structure (2) comprising a series of fins (11) connected to each other alternately by wave crests (10) and wave bases (12), characterized in that steps a) and b) are carried out simultaneously using the same forming tool (3, 4).

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