Method for manufacturing a heat exchanger by brazing a temperature probe, corresponding heat exchanger and temperature probe - Patents.com

Abstract

The present invention relates to a method for manufacturing a heat exchanger, comprising a step of assembling a temperature probe (6) to an element (4) of the exchanger by brazing, the temperature probe (6) being provided with a sheath. The method further comprises a step in which, before the assembling step, a thin coating is deposited on the sheath to prevent dissolution of the sheath by the alloy used as filler metal for the brazing. The present invention also relates to a heat exchanger obtainable by the above method, and to a temperature probe (6) prepared for implementing the above method.

Description

[Technical field]

[0001] The present invention belongs to the technical field of instrumentation for aluminum equipment, such as heat exchangers for air separation and / or hydrocarbon distillation, which are assembled in a brazing operation.

[0002] More specifically, the present invention relates to an assembly method for permanently assembling a temperature probe into the core of a heat exchanger structure, for example made of aluminum. [Background technology]

[0003] The state of the art contains publications on the need to instrument devices of the above mentioned type so as to be able to deduce their damage state when subjected to thermal loads, however, very few publications address how to instrument them, especially when it comes to obtaining thermal data representative of the temperature of the sheets separating the fluids.

[0004] The use of optical fibers integrated within the structure of the equipment has been described in the literature, but their use requires modifying the structure of the device by adding a non-active layer in which the fiber is located. The measured temperatures used to estimate the device lifetime are then unreliable, since they are only an approximation of the actual temperature at which the measured device structure is located.

[0005] Also known is French patent no. 3110099 (A1), whose proposed solution consists of cutting a groove in a metal sheet, in which a temperature probe (thermocouple) is subsequently placed. The brazed or non-brazed sheet is then covered with a second sheet. The assembly is then used in a structure as a single sheet separating the fluids.

[0006] A shim may also be pre-inserted into the groove and removed after brazing to allow the temperature probe to be inserted.

[0007] In a variant described in FR 3110098 A1, the temperature probe is inserted into the groove before brazing and the structure is brazed with the temperature probe already positioned in the groove. Following manufacture of the equipment, melting of the brazing filler joins the two sheets, permanently assembling the temperature probe to the structure and filling the groove in which the probe was inserted.

[0008] Both solutions make it possible to measure the temperature of the separator plate, but they are expensive and difficult to implement, given the size of the plate in which the grooves must be made. They necessarily lead to a significant thickening of the separator plate in which the temperature probe is installed.

[0009] The manufacture of grooves on thin flat products (on the order of mm) with large dimensions (on the order of meters) poses significant machining problems. In fact, very few machining units are capable of carrying out this type of operation. Other challenges remain with regard to the attachment of temperature probes to the structure of the device. For example, it is complicated to introduce a thermocouple with a cross section of about one millimeter or less into a cavity with a slightly larger diameter (as in French patent no. 3110099 (A1)) over a distance that can reach or exceed one meter.

[0010] Furthermore, there is a risk to the integrity of the probe if the thermocouple is sandwiched between two metal sheets which are then brazed together with the rest of the structure. In fact, the sheath thickness encapsulating the high-temperature solder of the thermocouple is insufficient to avoid being completely melted by the liquid solder, typically about 10% of the diameter value. This design therefore makes it impossible to guarantee accurate temperature measurement, or even measurement acquisition, if the heat-sensitive elements of the sensor are also melted.

[0011] The present invention aims to remedy the above-mentioned drawbacks by proposing a method for manufacturing a heat exchanger instrumented to measure temperature without modifying the architecture of the structure and without changing the characteristics of the temperature probe. Summary of the Invention

[0012] To this end, the invention relates to a method for manufacturing a heat exchanger, comprising a step of assembling a temperature probe to an element of the exchanger by brazing, said temperature probe comprising a sheath, said method further comprising a step of depositing, before the assembly step, a thin protective coating on said sheath, said coating being resistant to dissolution during brazing by the alloy used as filler metal.

[0013] The manufacturing method according to the invention includes a step consisting of protecting the sheath of the temperature probe (which may be a thermocouple) by depositing a protective coating before the brazing step.

[0014] The surface treatment with a thin protective layer limits the interaction between the liquid solder and the probe sheath, which may be, for example, a chemical reaction between the material forming the sheath and the filler alloy.

[0015] In this way, the method according to the invention allows the temperature probe to be permanently assembled into a heat exchanger (for example made of aluminum) without modifying its architecture or changing the operation of the sensor.

[0016] For example, unlike the known methods mentioned above, there is no need to create grooves for positioning the probes.

[0017] In this way, it is possible to preserve the integrity of the temperature probe during brazing of the structure without causing a significant thickening of the separator sheet to embed the temperature probe.

[0018] The proposed solution is therefore cheap, easy to implement and minimally intrusive whilst ensuring good long-term in-situ measurement quality.

[0019] According to an example embodiment, the heat exchanger is a brazed plate exchanger, with the temperature probe being joined to the fluid separator plate by brazing.

[0020] Advantageously, the coating may be formed by PVD, CVD or electroplating methods.

[0021] An advantage of these thin film manufacturing methods is that they are easy to implement on an industrial scale.

[0022] Advantageously, the thin coating may have a thickness of between 5 μm and 50 μm, which is sufficient to protect the sheath without interfering with the brazing.

[0023] Advantageously, the thin coating may comprise a metallic material that does not react with the alloy used as the braze filler metal, reducing or preventing reactivity with the filler alloy and ensuring sheath protection.

[0024] In one embodiment, the coating may include a superposition of two layers of different materials.

[0025] The coating material can be, for example, titanium and / or silver. It can be deposited as a single layer or as two separate layers, for example comprising a first coating of silver, for example 3-15 μm thick, and a second coating of titanium, for example having a thickness of 10-35 μm.

[0026] According to a second aspect, the invention relates to a heat exchanger obtained by the method according to the above description.

[0027] The present invention also relates to a temperature probe suitable for use in a heat exchanger manufacturing method as described above, the probe including a thin coating formed on a sheath to prevent dissolution of the sheath by the alloy used as the braze filler metal. [Brief description of the drawings]

[0028] Further features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. [Figure 1] 1 shows an embodiment of a stacked heat exchanger matrix. [Diagram 2] 1 shows a cross-sectional view of a matrix containing a temperature probe. [Diagram 3] FIG. 11 is a schematic cross-sectional view showing how the probe is brazed in place. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the following description, an example is described in which the resulting heat exchanger is a brazed plate wave exchanger, however, the invention is also applicable to other types of heat exchangers that can be instrumented by adding one or more braze temperature probes.

[0030] 1 shows a perspective exploded view of a matrix 2 of a brazed plate heat exchanger 1. The matrix 2 is shown stacked. It is made, for example, of aluminium, but according to variants it could also be made of other metals, such as steel.

[0031] As is known, the matrix 2 comprises a stack of components including in particular waves 3 , fluid separator plates (also called sheets) 4 and aluminium bars 5 which surround the waves 3 .

[0032] The heat exchanger 1 can be instrumented by adding one or more temperature probes to monitor temperature variations therein.

[0033] Figure 2 shows an embodiment of the invention in which a temperature probe 6 is attached to a separator plate 4. In the embodiment shown, the probe is positioned between two corrugated plates 3. In addition, the bar is cut into two portions 5' to allow the probe to pass through.

[0034] The probe 6 is used to measure the temperature of the separator plate 4 .

[0035] In other, not shown, embodiments, the bar need not be cut.

[0036] According to an embodiment, one or more probes (e.g., thermocouples) having a diameter of 0.25 to 1 mm can be used. The probes can be placed directly on the surface of the separator plate without disturbing the flow of fluid and can be assembled to the surface when the device is brazed.

[0037] Figure 3 shows an embodiment of a temperature probe 6 before (i) and after (ii) assembly by brazing with a separator plate 4. The separator plate 4 comprises a core 40, on which a braze filler 41 (comprising a braze filler alloy, for example an aluminium based braze filler alloy) is deposited.

[0038] The temperature probe 6 is placed on the plate 4 before brazing. This temperature probe is known per se and comprises an insulating material 60 surrounding a heat sensitive element 61, the whole assembly being covered by a protective sheath 62. It also comprises a connector 63 as shown in FIG.

[0039] To assemble the probe 6 on the plate 4, the plate 4 is placed in a brazing furnace after removal of the connector 63, which is only fitted in place after brazing.

[0040] Optionally, the cold joint end of the sheath can be sealed by laser welding prior to brazing. Alternatively, if the probe is too long, the portion remaining on the outside of the plate can be rolled up and mechanically attached to the instrument prior to brazing.

[0041] The furnace is heated to the brazing temperature, melting the brazing alloy 41 ′, which then partially or completely surrounds the probe and secures it to the plate 4 .

[0042] It is well known to those skilled in the art that temperature probes (thermocouples) are generally made from materials that are difficult to join by brazing, if the brazing material used is, for example, a low melting point aluminum alloy used in the manufacture of aluminum heat exchangers.

[0043] Aluminum is highly reactive with iron, nickel, and chromium, and when it comes into contact with them in the liquid state, it causes an exothermic reaction. This reactivity is sufficient to alter the sheath of a thermocouple, which is typically made of Inconel (a Ni-Cr-Fe alloy), affecting the measurement if the amount of liquid supplied when the solder melts is sufficient to melt the entire probe.

[0044] In order to protect the sheath during brazing, the method according to the invention includes a probe surface treatment step prior to the brazing step.

[0045] The surface treatment involves depositing a thin coating on the sheath to prevent the sheath from being dissolved by the alloy used as the braze filler metal. The thin coating limits the interaction between the liquid solder and the probe sheath without preventing the probe from being attached to the plate.

[0046] The coating can be formed by one of the following methods: PVD, CVD or electroplating, or any other means allowing a thin deposition of a metal layer capable of limiting the dissolution of the sheath while maintaining the ability to be assembled using a filler alloy.

[0047] The thin coating may include a metallic material that does not react with the alloy used as the braze filler metal.

[0048] Advantageously, the thin coating 64 may have a thickness of 5 μm to 50 μm. The coating material may be, for example, titanium and / or silver. It may be deposited as a single layer or as two separate layers, for example comprising a first coating of silver, for example of 3 to 15 μm, and a second coating of titanium, for example having a thickness of 10 to 35 μm.

Claims

1. 1. A method for manufacturing a heat exchanger (1), comprising the step of assembling a temperature probe (6) to an element (4) of the exchanger by brazing, the temperature probe (6) comprising a sheath (62), the method further comprising the step of depositing a thin coating (64) on the sheath (62) before the assembling step, the coating being resistant to dissolution during brazing by an alloy used as a filler metal for the brazing.

2. 2. The method for manufacturing a heat exchanger according to claim 1, wherein the heat exchanger (1) is a brazed plate exchanger and the temperature probe (6) is brazed to a fluid separator plate (4).

3. 2. The method for manufacturing a heat exchanger of claim 1, wherein the thin coating (64) is formed by a PVD method, a CVD method, or an electroplating method.

4. The method of claim 1, wherein the thin coating (64) has a thickness of between 5 μm and 50 μm.

5. The method of claim 1, wherein the thin coating (64) comprises a metallic material that does not react with the alloy used as a braze filler metal.

6. The method of claim 5 , wherein the thin coating comprises titanium and / or silver.

7. The method of claim 1 , wherein the thin coating (64) comprises a superposition of two layers of different materials.

8. The method of claim 7 , wherein the coating comprises a silver layer and a titanium layer.

9. A heat exchanger (1) obtainable by the method according to any one of claims 1 to 8.

10. 9. A temperature probe (6) suitable for use in a method for manufacturing a heat exchanger (1) according to any one of claims 1 to 8, characterized in that the probe (6) comprises a thin coating (64) formed on the sheath (62) to prevent dissolution of the sheath (62) by an alloy used as a brazing filler metal.

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