Method for producing heat exchanger by brazing temperature probe, corresponding heat exchanger and temperature probe

Abstract

The 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) comprising a sheath. The method further includes a step prior to the assembly step in which a thin coating is deposited on the sheath so as to prevent the sheath from being corroded by the alloy used as the filler metal of the braze. The invention also relates to the heat exchanger obtainable by the method and to the temperature probe (6) produced for implementing the above-mentioned method.

Description

Technical Field

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

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

[0003] Prior art includes publications on the need to instrument a device of the type described above in order to be able to deduce the damage state of the device when subjected to thermal loads. However, few publications deal with how to instrument the device, particularly when it comes to obtaining thermal data representative of the temperature of a sheet separating a fluid.

[0004] The use of optical fibers integrated inside the structure of the device is mentioned in the literature, but the use of optical fibers requires modifying the structure of the device by adding an inactive layer in which the optical fiber is placed. Therefore, the measured temperatures used to estimate the lifetime of the device are unreliable, as they are only an approximation of the actual temperature at which the device structure is measured.

[0005] Also known is FR3110099A1, which proposes a solution consisting in cutting a groove in a metal sheet, in which a temperature probe (thermocouple) is subsequently placed. The brazed or unbrazed sheet is then covered by a second sheet. The assembly then acts in this structure as a single sheet for separating fluids.

[0006] The shims are also pre-inserted into the grooves and are removed after brazing to allow the temperature probe to be inserted.

[0007] In a variant described in FR3110098A1, the temperature probe is inserted into the groove before brazing, and the structure is brazed together with the temperature probe already positioned in the groove. After manufacturing the device, 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 has been inserted.

[0008] Although both solutions enable the temperature of the partition plate to be measured, they are expensive and difficult to implement, given the size of the plate in which the grooves must be made. They inevitably lead to a significant thickening of the partition plate where the temperature probe is mounted.

[0009] The production of grooves on thin flat products (about one millimeter) with large dimensions (about one meter) presents serious machining problems. In fact, very few machining units can perform this type of operation. There are also other difficulties with the structure of attaching the temperature probe to 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 FR3110099A1) over a distance that can reach or exceed one meter.

[0010] Furthermore, there is a risk regarding the integrity of the probe if the thermocouple is sandwiched between two metal sheets that are then brazed to the rest of the structure. In fact, the thickness of the sheath of the hot solder encapsulating the thermocouple is not sufficient to avoid complete corrosion by the liquid solder, which thickness is usually about 10% of the diameter. Therefore, this design makes it impossible to guarantee accurate temperature measurements, or even measurement acquisition, if the thermal element of the sensor is also corroded.

[0011] The present invention aims to remedy the above-mentioned drawbacks by proposing a method of 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 comprising a sheath to an element of the exchanger by brazing. The method further comprises a step before the assembling step in which a thin protective coating is deposited on the sheath, said coating being resistant to corrosion by the alloy used as filler metal during brazing.

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

[0014] The surface treatment with a thin protective layer limits the interaction between the liquid solder and the probe sheath. The interaction 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 enables a temperature probe to be permanently assembled in a heat exchanger (for example made of aluminium) without modifying its architecture or changing the operation of the sensor.

[0016] For example, unlike the known method described above, it is not necessary to produce a groove for positioning the probe.

[0017] In this way, the integrity of the temperature probe can be maintained during brazing of the structure without causing a significant thickening of the separator sheet due to the implantation of the temperature probe.

[0018] Therefore, the proposed solution is cheap and easy to implement, minimally invasive, while guaranteeing good long-term in situ measurement quality.

[0019] According to an embodiment example, the heat exchanger is a brazed plate exchanger, wherein the temperature probe is bonded to the fluid separation plate by brazing.

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

[0021] The advantage of these thin film fabrication methods is that they are easily implemented on an industrial scale.

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

[0023] Advantageously, the thin coating may comprise a metallic material that is non-reactive with the alloy used as the brazing filler metal. This reduces or prevents reactivity with the filler alloy and ensures sheath protection.

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

[0025] The coating material may be, for example, titanium and / or silver. It may be deposited as a single layer or in two different layers, including, for example, a first silver coating (eg from 3 μm to 15 μm) and a second titanium coating (eg having a thickness between 10 μm and 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 the heat exchanger manufacturing method as described above, the probe comprising a thin coating formed on a sheath to prevent the sheath from being eroded by an alloy used as a brazing filler metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Additional features and advantages of the present invention will become apparent from the following detailed description, which can be understood with reference to the accompanying drawings, in which:

[0029] [ Figure 1 ][ Figure 1 ] shows an example of a stacked heat exchanger matrix.

[0030] [ Figure 2 ][ Figure 2 ] shows a cross section of a substrate containing a temperature probe.

[0031] [ Figure 3 ][ Figure 3 ] is a schematic vertical cross-section showing how the probe is brazed in place. DETAILED DESCRIPTION

[0032] In the following description we describe examples where the resulting heat exchanger is a brazed plate wave exchanger. However, the invention is also applicable to other types of heat exchangers which can be instrumented by adding one or more temperature probes brazed thereon.

[0033] [ Figure 1 ] shows an exploded perspective view of a base body 2 of a brazed plate heat exchanger 1. The base body 2 is shown as laminated. It is made of aluminum, for example, but can also be made of other metals (such as steel) according to variants.

[0034] In a known manner, the base body 2 comprises a stack of components, in particular a corrugation 3 , a fluid separation plate (also called sheet) 4 and an aluminium strip 5 surrounding the corrugation 3 .

[0035] The heat exchanger 1 may be instrumented by adding one or more temperature probes to monitor internal temperature changes.

[0036] [ Figure 2 ] shows an example of the invention in which a temperature probe 6 is attached to a separator plate 4. In the example shown, the probe is positioned between two corrugated plates 3. In addition, the strip is cut into two parts 5' to allow the probe to pass through.

[0037] The probe 6 is used to measure the temperature of the partition plate 4 .

[0038] In other examples not shown, the strips need not be cut.

[0039] According to an embodiment, one or more probes (eg thermocouples) having a diameter between 0.25 mm and 1 mm may be used. The probes may be placed directly on the surface of the separator plate without disturbing the flow of the fluid and assembled on the surface when the device is brazed.

[0040] [ Figure 3 ] shows an example of a temperature probe before (i) and after (ii) assembling the temperature probe 6 with a separator plate 4 by brazing. The separator plate 4 comprises a core 40 on which a brazing filler 41 (comprising a brazing filler alloy, such as an aluminum-based brazing filler alloy) is deposited.

[0041] Before brazing, a temperature probe 6 is placed on the plate 4. Such a temperature probe is known and comprises an insulating material 60 surrounding a thermal element 61, and the whole assembly is covered by a protective sheath 62. It also comprises a protective cover 62 as shown in [ Figure 2 ]Connector 63 shown in ].

[0042] To assemble the probe 6 on the board 4 , the board is placed in a brazing furnace after removing the connector 63 , which will be put in place only after brazing.

[0043] Optionally, the cold junction end of the sheath may be sealed by laser welding before brazing. Alternatively, before brazing, if the probe is too long, the portion remaining outside the plate may be rolled up and mechanically attached to the device.

[0044] The furnace is heated to the brazing temperature and melts the brazing alloy 41 ′. This alloy then partially or completely surrounds the probe and fixes it to the plate 4 .

[0045] It is known to the person skilled in the art that temperature probes (thermocouples) are often made of materials that are difficult to join by brazing if the brazing flux used is a low melting point aluminum alloy, such as is used in the manufacture of aluminum heat exchangers.

[0046] Aluminum is highly reactive with iron, nickel, and chromium, causing an exothermic reaction when aluminum in its liquid state comes into contact with them. This reactivity is sufficient to alter the sheath of thermocouples, which are typically made of Inconel (a Ni-Cr-Fe based alloy), and affect measurements if the amount of liquid supplied is sufficient to dissolve the entire probe when the solder melts.

[0047] In order to protect the sheath during brazing, the method according to the invention comprises a probe surface treatment step prior to the brazing step.

[0048] Surface treatment involves depositing a thin coating on the sheath to protect it from dissolution by the alloy used as brazing 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 board.

[0049] The coating may be formed by one of the following methods: PVD, CVD or electroplating, or by any other means capable of depositing a thin layer of metal that is capable of limiting erosion of the sheath while maintaining the ability to be assembled using a filler alloy.

[0050] The thin coating may include a metallic material that is non-reactive with the alloy used as the brazing filler metal.

[0051] Advantageously, the thin coating 64 may have a thickness between 5 μm and 50 μm. The coating material may be, for example, titanium and / or silver. It may be deposited as a single layer or in two different layers, including, for example, a first silver coating (e.g. from 3 μm to 15 μm) and a second titanium coating (e.g. having a thickness between 10 μm and 35 μm).

Claims

1. A method for manufacturing a heat exchanger (1), said method comprising a step of assembling a temperature probe (6) to an element (4) of said exchanger by brazing, said temperature probe (6) comprising a sheath (62), said method being characterized in that said method further comprises a step before the assembling step, in which a thin coating (64) is deposited on said sheath (62), said coating being resistant to corrosion during brazing by an alloy used as a filler metal for said brazing.

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

3. Method for producing a heat exchanger according to one of the preceding claims, wherein the thin coating (64) is formed by a PVD, CVD or electroplating method.

4. Method according to one of the preceding claims, wherein the thin coating (64) has a thickness between 5 μm and 50 μm.

5. The method according to one of the preceding claims, wherein the thin coating (64) comprises a metallic material which does not react with the alloy used as brazing filler metal.

6. Method according to the preceding claim, wherein the thin coating comprises titanium and / or silver.

7. Method according to one of the preceding claims, wherein the thin coating (64) comprises a superposition of two layers of different materials.

8. Method according to the preceding claim, wherein the coating comprises a layer of silver and a layer of titanium.

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

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

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