Method of manufacturing an interlayer element for a heat exchanger

Abstract

Title of the invention: Method for manufacturing an insert element for a heat exchanger Method for manufacturing an insert element for a plate and fin type heat exchanger, said method comprising the following steps: a) carrying out a surface texturing on at least part of the surface of a sheet (1), b) obtaining a corrugated structure (2) by deformation of said sheet, said corrugated structure comprising a series of fins (11) connected to each other alternately by wave tops (10) and wave bases (12), characterized in that steps a) and b) are carried out simultaneously by means of 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 of manufacturing an interlayer element for a plate and fin type heat exchanger.

[0002] The present invention finds application in particular in the field of cryogenic gas separation, in particular 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 which vaporizes a liquid flow, for example liquid oxygen, nitrogen and / or argon by heat exchange with a calorigenic gas, for example air or nitrogen.

[0003] If the heat exchanger is located in the tank of a distillation column, it can constitute a vaporizer operating as a thermosiphon for which the exchanger is immersed in a bath of liquid descending the column or a vaporizer operating in film vaporization 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 with 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 equipment.

[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 aluminum exchangers with brazed plates and fins or waves, which make it possible to obtain very compact devices offering a large exchange surface.

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

[0009] The role of the intercalary elements is to increase the contact surface between the fluids and the walls of the exchanger in order to promote heat exchange. The performance of an exchanger is linked to the heat exchange 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 fluid flow regime.

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

[0011] The increase in the exchange surface is generally linked to the density of the corrugated interlayer element used, generally expressed in terms of the number of fins per unit length. However, the possibility of increase is limited since the greater the density of fins, the greater the pressure drop generated. There is therefore a compromise allowing the exchange surface to be increased without it generating too great a pressure drop. In particular, in the case of vaporizer-condenser type exchangers, the increase in the exchange surface is limited by the maximum density of the wave that can be used in the vaporization passages. Indeed, for safety reasons linked to the vaporization of oxygen and the risks of impurity deposits and channel blockages, it is recommended to use straight waves without obstacles while respecting a minimum channel width.

[0012] Concerning the increase in the heat exchange coefficient, this can be obtained by modifying the physicochemical properties of the exchange surfaces. This makes it possible to increase the effective exchange surface and / or to modify the interactions between the fluid and the surface, by changing the properties of the surface considered as its wettability or its capacity to intensify the boiling of a fluid. We then speak of texturing the exchange 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 intermediate elements, in particular by mechanical treatments or by chemical attack.

[0014] A problem that arises with the implementation of texturized intensified surfaces in brazed aluminum exchangers concerns the actual production of the surface texturizations.

[0015] Indeed, due to their reduced dimensions, it is difficult to access the channels formed by the corrugated structures of the intermediate elements. The intermediate 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. In addition, these access difficulties make the texturing operations more complex and longer, several coating passes may be necessary, which results in additional manufacturing costs.

[0016] It then becomes difficult, or even 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 prior steps of heat treatment or deposition of an impregnation layer to ensure adhesion of the coating, it is the entire exchanger that must be treated. There are then risks of blocking the channels, of debrazing parts of the exchanger or of creating fragile metallurgical phases and damaging the brazed matrix.

[0017] As an alternative, it has been proposed to carry out surface texturing on the separating plates before brazing. But in this case, there is no interlayer brazed to the plates and it is necessary to anneal the plates. However, the interlayers also have a role as spacers. They contribute to the rigidity of the exchanger passages and their compressive strength during vacuum brazing of the exchanger. In addition, the annealed plates lose their mechanical strength. It is then necessary to arrange additional reinforcing bars in the passages and to double the thickness of the plates.

[0018] It has also been proposed to produce surface texturing on a flat sheet before it is formed into a corrugated shape. In this configuration, shaping the sheet by folding is difficult to achieve without damaging the surface texturing. Indeed, folding a flat sheet is an operation which violently compresses the flat sheet with a rectangular-shaped tool in a groove of complementary shape. In the case of texturing obtained by depositing porous material, tearing of the material can therefore occur and damage the folding mechanism itself.

[0019] Another solution is to carry out the surface texturing after brazing the exchanger, but in this case texturing by mechanical means or by projection is not possible. And if the texturing is carried out by another coating technique, a subsequent heat treatment may be necessary to ensure the adhesion of the coating. This heat treatment must then be carried out on the entire exchanger, at the risk of debrazing parts of the exchanger or creating fragile metallic phases within these parts.

[0020] When one wishes to improve the thermal efficiency of an exchanger, one must therefore not only consider the operating performance of the exchanger but also its manufacturing method.

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

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

[0023] a) carrying out a surface texturing on at least one surface of a sheet,

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

[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 thanks to the description which follows, given solely by way of non-limiting example and made with reference to the attached diagram:

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

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

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

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

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

[0032] As seen in [Fig.l], within an exchanger passage 20, corrugated structures 11 may be superimposed. Said corrugated structures 11 comprise wave tops and wave bases 10, 12 of two different types, textured planes, in particular grooved, or non-planar.

[0033] In the context of the invention, the surface texturing may result from a surface coating deposited on the element or from a modification of the surface state of said element.

[0034] In particular, the surface texturing may result from a surface coating deposited on the interlayer 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 spraying, in particular by flame or by 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, etc.

[0036] According to a preferred embodiment, the surface texturing is in the form of a porous material. The porous material may for example be formed from a deposit of slightly sintered aluminum particles, entangled aluminum filaments, semi-molten aluminum particles stuck to each other, such as the aluminum particles which are obtained after projection which is obtained by thermal projection by flame or by plasma.

[0037] Preferably, the surface texturing has an open porosity of between 15 and 60%, preferably between 20 and 45%, more preferably an open porosity of between 25 and 35% (% by volume). Note that the 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 intermediate element in question is located, and the total volume of the porous structure.

[0038] Alternatively, the surface texturing may be in the form of reliefs, or patterns, printed or produced 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 or various sizes or morphologies, such as grooves, discrete or uninterrupted, striations, protuberances, etc., may be formed or deposited on the surface of the element in question. In particular, the reliefs forming the surface texturing may be produced by laser or mechanical and / or chemical machining.

[0039] The intercalary element manufactured according to the invention may have a height, measured orthogonally to the wave peaks or bases, of between 3 and 10 mm. The peaks, the wave bases, the fins may have a thickness of between 0.1 and 0.6 mm. The peaks, the 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 method according to the invention is a straight wave having a single series of fins with flat surfaces, each fin forming a strip which extends across the entire width or length of the passage. The use of straight waves simplifies the manufacture of the interlayer element and is advantageous in particular in exchanger passages provided for the flow and vaporization of oxygen because their geometry limits the risks of deposits of impurities and channel plugging. The wave peaks and bases are planar in shape and extend parallel to each other and perpendicular to the fins. The channels formed between two successive fins and a peak or base arranged between said successive fins thus have cross-sections of a generally square or rectangular shape.

[0042] As seen in Figures 2 to 5, a sheet 1 is introduced along 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 outlet of the forming tool. Said corrugated structure comprises a series of fins 11 connected to each other alternately by wave tops 10 and wave bases 12.

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

[0044] The thickness of the sheet metal may increase after texturing. The spacing between the jaws of the forming tool may be adjusted relative to a sheet metal without texturing. In addition, it is possible to maintain the texturing on the bases and peaks of the wave by also adjusting the spacing between the jaws and the spacers at the end of the tool stroke. Said spacing may be between 0.02 mm and 0.1 mm. Conversely, it is possible to reduce or eliminate the texturing on the bases and peaks of the wave for a spacing between 0 and 0.05 mm.

[0045] Preferably, the ratio between the height and the width of the wave peaks or bases is between 1 and 2. In the case of a texturing 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 interest in producing a textured wave is twofold. A textured wave makes it possible to increase the exchange surface of the wave and therefore the performance of the exchanger. A textured wave also makes it possible, thanks to the geometry of the texturing, to improve the local exchange coefficient due to the impact of the thickness of the liquid film in the case of vaporization or condensation, or due to the local turbulence generated.

[0047] Preferably, geometric dimensions for improving condensation or vaporization of fluids will be applied to the grooves. Said geometric dimensions are ridge heights of between 0.05 mm and 0.4 mm, groove pitches of between 0.3 mm and 1 mm and ridge thicknesses of 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] Claims A method of manufacturing an interlayer element for a plate-fin heat exchanger, said method comprising the following steps: - a) carrying out surface texturing on at least part of the surface of a sheet metal (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 tops (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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