GB2049150A - Making a heat exchanger - Google Patents

Abstract

Assembling a finned tube sealingly into a partition (15) is difficult and therefore expensive. According to the invention an inner tube (16a) is threaded through the partition (15) and pre-finned sleeve lengths (17a, and 17c) introduced thereover and the tube (16a) is substantially expanded into sealing engagement with the partition and tight engagement with the finned sleeving. The tube may be simultaneously assembled to tube plates (11). The invention is particularly useful in the assembly of heat pipe heat exchangers. The tube (16a) may be of copper and the sleeve lengths (17) may be of aluminium. The fins may be helical. <IMAGE>

Description

SPECIFICATION Improved heat exchanger This invention relates to heat exchangers in which finned tubes extend through partitions.

One such heat exchanger, to which the invention is particularly but not solely applicable is a heat exchanger incorporating so called heat pipes. A heat pipe is exposed to two, or more, external fluid streams at different temperatures, separated by a partition through which the heat pipes extend. The or each heat pipe itself is a sealed tube or pipe containing a small amount of a liquid which is arranged to evaporate and condense at different zones of the heat pipe so as to tend to maintain an even temperature at the surface thereof, thereby transferring heat from a zone of the heat pipe in a high temperature stream to a zone thereof in a lower temperature stream.In order to obtain a good heat transfer between the fluid streams, which are normally gaseous, and the heat pipes, it is desirable for the heat pipes to be finned, but it will be appreciated that passing a finned tube through a partition and obtaining a good seal is a difficult and therefore expensive operation.

According to the invention, there is provided a method of making an assembly of a finned tube passing through a preformed aperture in one or more partitions, in which an inner tube is introduced through the preformed aperture and through at least one prefinned sleeve and is subsequently relatively expanded into tight engagement with the aperture and pre-finned sleeve.

In this way, the inner tube can be secured to the partition and sleeve or sleeves in one operation, and can be secured to casing parts in the same expansion operation.

As an alternative, the partition and sleeve or sleeves may be contracted, e.g. thermally, into tight engagement.

The invention further includes assembling a plurality of finned tubes into one or more partitions by introducing successive inner tubes through performed apertures in the partitions and through pre-finned sleeves and subsequently relatively expanding the inner tubes into engagement with the apertures and pre-finned sleeved.

The or each pre-finned tube is preferably helically finned.

The invention further includes a heat ex changer including an assembly of one or more finned tubes and a partition when assembled by a method as set forth above.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is an elevation of a form of gas/ gas heat exchanger incorporating finned heat pipes; Figure 2 is a transverse section on the line A-A of Fig. 1; and Figure 3 is a longitudinal section, to an enlarged scale, showing parts prior to the completion of assembly.

The heat exchanger illustrated in Figs. 1 and 2 includes two tube plates 11 having flanges 12, and also top and bottom plates 13 having flanges 14. A partition 15 divides the volume enclosed by the plates 11 and 13 into two flow spaces for gaseous fluids to be in heat exchange with one another. The basic heat exchange mechanism is by heat pipes 16 which have helical fins, as shown at 17, in the flow spaces for the gaseous fluids. A small quantity of a suitable liquid is sealed within each heat pipe 16 and evaporates within the hotter flow space and condenses in the cooler one to transfer heat from the hotter one to the cooler.

In order to ensure that the heat pipes 16 are sealed to preformed apertures in the tube plates 11 and the partition 15, and also properly finned within the flow zones, assembly is carried out by a method to be described in greater detail with reference to Fig. 3. An inner tube 1 6a, e.g. of one inch (2.54 cm) outside diameter in 16 swig copper, of each heat pipe is threaded through an aperture in one tube plate 11 and at the same time introduced into one or more lengths 17 of pre-finned sleeving of a length to fit, with minimum clearance, between the tube plate 11 and the partition 15. For example, the prefinned sleeving may be of aluminium of 2.1/4 inches (5.12 cm) outside diameter, with ten fins per inch, (2.54 cm), with an internal diameter slightly greater than one inch (2.54 cm).The clearance between the inner tube 1 6a and the inner diameter 1 7b of the finned sleeve 1 7a is shown somewhat exaggerated in Fig. 3 for clarity of illustration.

The tube 1 6a is then introduced through the aperture in the partition 15 and into one or more further lengths 1 7c of a similar finned sleeving. Continued introduction of the inner tube 1 6a results in it passing through the aperture in the opposite tube plate 11 (not shown in Fig. 3). When the tube is in position, it is expanded by an appropriate metal expansion technique, normally mechanical in nature but it could be hydraulic, to ensure that the inner tube fits tightly in the apertures in the tube plates 11 and partition 15 and is also tightly bonded to the sleeve lengths 1 7a and 17c.

Each heat pipe is individually assembled in this manner from an inner tube and two, in the case illustrated, but it could be more, lengths of finned sleeving.

It will be appreciated that in appropriate cases there may be more than one partition between the tube plates 11, and the method may also be applied to such arrangement.

Various modifications may be made within the scope of the invention. For instance, the tube plates, pre-finned sleeve length and partition may be hot while the inner tube is assembled through them and then allowed to contract into sealing engagement therewith. A mechanical expansion of the inner tube may be used in conjunction with this method of assembly.

It will be appreciated that by use of prefinned sleeves fitting over the inner tubes, the problems of finning in the confined space between the tube plates and partition are avoided, and also the inner tube itself may be substantially completely covered by the finned sleeve. These lead to reduction in manufacturing costs and improved operating efficiency.

The pre-finned sleeving may be an integral extruded fin sleeve or it may be in the form of an inner tube having a fin formed thereon by extrusion of an outer sleeve or it may be a tube to which any type of finning has been applied.

Claims (11)

1. A method of making an assembly of a finned tube passing through a preformed aperture in one or more partitions, in which an inner tube is introduced through the preformed aperture and through at least one prefinned sleeve and is subsequently relatively expanded into tight engagement with the aperture and pre-finned sleeve.

2. A method of making an assembly of a plurality of finned tubes passing through one or more partitions by introducing successive inner tubes through preformed apertures in the partitions and through pre-finned sleeves and subsequently relatively expanding the inner tubes into engagement with the apertures and pre-finned sleeves.

3. A method as claimed in claim 1 or 2, in which the inner tube is secured to casing parts in the same relative expansion operation.

4. A method as claimed in claim 1, 2 or 3, in which the inner tube is mechanically expanded.

5. A method as claimed in claim 1, 2, 3 or 4, in which the partition and/or sleeve or sleeves is or are thermally contracted onto the inner tube.

6. A method as claimed in any of the preceding claims, in which the or each prefinned tube is helically finned.

7. A method as claimed in claim 6, in which the or each preformed tube is formed with an integral extruded fin.

8. A method of making an assembly of one or more finned tubes and one or more partitions substantially as hereinbefore described with reference to the accompanying drawings.

9. An assembly of one or more finned tubes and one or more partitions when made by a method as claimed in any of the preceding claims.

10. A heat exchanger including an assembly of one or more finned tubes and one or more partitions as claimed in claim 9.

11. A heat pipe heat exchanger having finned heat pipes assembled by a method as claimed in any of claims 1 to 8.