GB2117503A - Heat exchanger tube support plate - Google Patents

Abstract

A tube support system is provided which utilizes a generally flat plate with a plurality of holes formed therethrough and tubular sleeve members disposed in the holes and metallurgically bonded to the plate. Each tubular member is shaped to receive a heat exchanger tube in sliding relation. The tubular sleeve members are made of an appropriate material such as a nickel- based alloy which reduces wear and galling of its associated heat exchanger tube when the tube is made of chromium- molybdenum steel. <IMAGE>

Description

SPECIFICATION Heat exchanger tube support plate The present invention relates generally to heat exchangers and, more specifically, to tube support plates which provide lateral support for heat exchan- ger tubes.

In heat exchangers which use a plurality of tubes, a heated fluid is passed through the central bore of the tubes and is cooled by the transfer of heat through the walls of the tubes to another fluid which flows around the outer surface of the tubes. Heat exchangers of this type operate with a primary loop of heated fluid and a secondary loop of a separate and distinct fluid which is to be heated by the above-described thermal transfer. The fluids in the primary and secondary loops do not come into contact with each other, but are in thermal communication with each other through the walls of the above-mentioned plurality of tubes. When the heat exchangers of this type utilize tubes of a significant length, lateral support must be provided to prevent the tubes from either sagging or buckling due to thermal stresses.

This lateral support is generally provided by a plurality of tu be support plates spaced a preselected distance apart within the heat exchanger and along the length of the tubes. These tube support systems generally consist of one or more generally flat plates disposed in a plane which is perpendiculartothe tubes. Each plate has a plurality of holes therethrough which are shaped to receive the tubes in sliding relation and the function of these support plates is to prevent significant lateral movement of the tubes while allowing them to linearly expand and contract as their temperatures change.Therefore, it is necessary for the tube support plates to be designed in such a way as to permit the tubes to slide axially through their holes while preventing the tubes from moving in a lateral direction perpendiculay to the respective center lines and parallel to the plane of the support plates.

In heat exchangers where tube support plates are used, damage to the tube can occur when relative motion between the tubes and their support plates occurs or where corrosion causes a penetration of the walls of the tubes. Also, if the tubes become seized within the support plate, the tubes can experience buckling loads caused by thermal expansion and contraction because of the reduced linear freedom of movement. To prevent these problems when steel tubes are used, it is recommended that the portion of the tube support plate with which the steel tubes are in contact be made from a nickel based alloy, such as Inconel 718. This combination of materials provides wear resistance which is required when side loads are excessive on the tubes.

To further prevent galling of the tubes within the support plate, the nickel based alloy can also be aluminized.

In heat exchangers where the tube support plates are of significant size, the cost of the use of a nickel based alloy for their manufacture can be prohibitive.

It is therefore the principal object of the present invention to provide a tube support system for use in heat exchangers which prevents damage to the tubes while minimizing the cost of its manufacture.

With this object in view, the present invention resides in a heat exchanger comprising: a plurality of tubes supported by at least one tube support plate (10) having a plurality of holes extending therethrough, each receiving a preselected one of said plurality of tubes (20), characterized by a plurality of tubular sleeves (12), each being disposed in a preselected one of said plurality of holes, each of said plurality of sleeves (12) being rigidly connected to said tube support plate (10), and being shaped to fittingly receive a preselected one of said plurality of tubes (20) in sliding relation. The length of each of these tubular sleeve members is such that it extends entirely through the thickness of the tube support plate and may extend beyond the surfaces thereof.

The tubular sleeve members are made of a material which has the above-described wear characteristics, such as a nickel-based alloy.

In order to provide a rigid connection between each of the tubular sleeve members and the tube support plate, the tubular members are diffusion bonded to the plate. After the tubular members are disposed within the holes of the tube support plate, the entire assembly is raised to a temperature in excess of 760"C for a preselected period of time to induce diffusion bonding. It has been found that the diffusion bonding operation is facilitated by an interference fit between the tubular sleeve members and their associated holes in the tube support plate.

Higher pressures between these components reduces the required temperature and time for bonding to be achieved. This interference fit can be accommodated by heat shrinking each of the tubular sleeve members into its associated hole in the tube support plate. Each of the above-described tubular sleeve members is shaped to receive one of the heat exchanger tubes in sliding relation.

The relative diametrical sizes of the tubular sleeve members and their associated heat exchanger tubes are chosen to provide adequate lateral support to prevent movement of the tubes within the piane of the tube support plate but also to permit linear sliding which allows for axial expansion and contraction of the tubes to prevent their buckling under thermal loads.

It should be apparent that the present invention incorporates a tube support system for heat exchangers which provides both lateral support and axial freedom of movement for the tubes while minimizing the cost of its manufacture. It should also be apparent that the tube support system of the present invention minimizes galling and wearing of the tubes within their tube support plates by providing a contact surface of a nickel-based alloy without the need for manufacturing the entire tube support plate of this more expensive material.

The invention will become more readily apparent from the foilowing description of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings, wherein: Figure 7 illustrates an exemplary section view of a hole through the tube support plate of the present invention with a tubular member disposed therein; and Figure 2 depicts a tube support system made in accordance with the present invention showing a plurality of heat exchanger tubes disposed therethrough.

The present invention relates generally to heat exchangers which utilize a plurality of tubes and, more specifically, to a tube support system which provides lateral support for the tubes while allowing them to slide axially through the tube support system.

As illustrated in Figures 1A and 1B the tube support plate 10 of the present invention has tubular sleeve members 12 disposed in holes extending through the plate 10. The inner cylindrial surface 14 of the hole and the outer cylindrial surface 16 of the tubular sleeve member 12 are diffusion bonded together. After assembly of the tubular sleeve members 12 into the tube support plate 10, the diffusion bonding operation can be performed by raising the assembly to a temperature in excess of 760 C. Prior to the diffusion bonding operation, the assembly of each tubular sleeve member 12 within the plate 10 can be provided with an interference fit between the inner surface of 14 of the hole and the outer surface 16 of the tubular sleeve member 12. This interference fit provides a positive contact between these associated members.This positive contact facilitates the diffusion bonding operation and maintains the position of the tubular sleeve member 12 within the tube support plate 10 prior to and during the diffusion bonding procedure. It should be understood that the pressure between these components is inversely related to the required bonding temperature. Therefore, a higher pressure caused by a significant interference fit reduces the required bonding temperature and the time during which this temperature must be maintained. The inner cylindrical surface 18 of the tubular sleeve member 12 is shaped to receive a tube of the heat exchanger in sliding relation.

In Figure 1A, the tubular sleeve member 12 is shown protruding beyond one planar surface of the tube support plate 10 whereas in Figure 1 B the axial ends of the tubular sleeve member 12 are shown flush to be flush with both planar surfaces of the tube support plate 10. It should be understood that both these variations, along with the alternative of having the tubular sleeve members 12 protruding beyond both planar surfaces of the tube support plate 10, are within the scope of the present invention. These variations of the preferred embodiment of the present invention merely represent design alternatives which can vary as a function of performance and manufacturing considerations.

Figure 2 shows a more detailed view of the tube support plate 10 of the present invention with a plurality of tubular sleeve members 12 disposed in holes which extend through it. Also shown in Figure 2 are a plurality of flow holes 13 through which a fluid can pass. These flow holes 13 can vary in number, size and location depending on the specific design considerations of the heat exchanger of which the present invention is a component. It should be understood that these flow holes 13 allow a fluid to pass through the tube support plate 10 and flow to the various regions of the heat exchanger which are divided by the tube support plates 10 of the present invention. Each of the tubular sleeve members 12 is shown in Figure 2 with a heat exchanger tube 20 extending through it in concentric and coaxial relation.The inner cylindrical surface of each tubular sleeve member 12 is shaped to receive one of the tubes 20 in sliding relation. Each association of a tube 20 within a tubular sleeve member 12 is provided with a clearance 22 which permits the tubes 20 to slide within the tubular sleeve member 12 in the axial direction shown by arrow A. However, it should be apparent that the minimal clearance 22 must be limited so that it does not permit a significant lateral movement in the direction shown by arrow L.

Each tubular sleeve member 12 is made of a material which will minimize galling and wear of its associated tube 20. When the tubes 20 are made of a chromium-molybdenum steel, a tubular sleeve member 12 made of a nickel-based alloy, such as Inconel 718, satisfies this criterion. Since the tubes 20 do not come into direct contact with the tube support plate 10, the plate 10 can be made of a much less expensive material such as a chromiummolybedeum steel.

Each tubular sleeve member 12 is diffusion bonded to the tube support plate 10 by raising these components to a temperature in excess of 760"C. To facilitate the diffusion bonding, the outer cylindrical surface 16 of the tubular sleeve member 12 and the inner cylindrical suface 14 of the hole are shaped to be associated in an interference fit. This interference fit provides positive contact between these two members which not only aids in the diffusion bonding procedure but also retains the tubular sleeve member 12 within its associated hole prior to and during the diffusion bonding operation. The assembly of the tubular sleeve member 12 into its associated hole can then be accomplished by either raising thetemperture of the plate 10 or lowering the temperature of the tubular sleeve member 12.This temporary differential in temperature will eliminate the diametrial interference during assembly until the temperatures of the tubular sleeve member 12 and the plate 10 equalize.

It should be apparent that the present invention provides a tube support system, for use in heat exchangers, which supports the tubes laterally while allowing axial movement therethrough. It should also be apparent that the present invention allows relatively inexpensive materials to be used for the construction of the tube support plate while utilizing more wear resistant materials for construction of the contact surfaces between the tube support system and the heat exchanger tubes.

It should be understood that although the present invention has been described in particular detail, it should not be construed to be so limited. Specifically, the choices of materials described above are a function ofthe particular application ofthetube support system and the material with which the heat exchanger tubes are made. In other applications, where the heat exchanger tubes are made of alternate materials, the tube support system of the present invention could also be made of alternate materials. Although the present invention has been described above utilizing chromium-molybednum steel for its support plate and a nickel-based alloy for its tubular members, other choices of suitable materials should be considered as being within its scope.

The United States Government has rights in this invention pursuant to Contract No. DE-AC-02-77-ET37201 awarded by the Department of Energy.

Claims (6)

1. A heat exchanger comprising: a plurality of tubes supported by at least one tube support plate (10) having a plurality of holes extending therethrough, each receiving a preselected one of said plurality of tubes (20), characterized by a pluraity of tubular sleeves (12), each being disposed in a preselected one of said plurality of holes, each of said plurality of sleeves (12) being rigidly connected to said tube support plate (10), and being shaped to fittingly receive a preselected one of said plurality of tubes (20) in sliding relation.

2. A heat exchanger as claimed in claim 1, characterized in that each of said plurality of tubular sleeves (12) is metallurgically bonded to said tube support plate (10) by diffusion bonding.

3. A heat exchanger as claimed in claim 2, characterized in that said diffusion bonding is achieved by heating said tube support plate and said plurality of tubes to a temperature in excess of 760"C.

4. A heat exchanger as claimed in claim 1,2 or 3, characterized in that said tube support plate (10) consists of steel and each of said plurality of tubular sleeves (12) consists of a nickel alloy.

5. A system as claimed in claim 1, characterized in that each of the plurality of tubes (20) is shrinkfitted into a preselected one of said plurality of holes.

6. The system of claim 1, characterised in that said sleeves (12) are expanded against the inner surface of said holes.