GB2197449A

GB2197449A - Heat exchange tube

Info

Publication number: GB2197449A
Application number: GB08626585A
Authority: GB
Inventors: Eric Smith
Original assignee: PENTAGON RADIATOR
Current assignee: PENTAGON RADIATOR
Priority date: 1986-11-06
Filing date: 1986-11-06
Publication date: 1988-05-18
Anticipated expiration: 2006-11-06
Also published as: GB2197449B; GB8626585D0

Abstract

A heat exchange tube shown in end elevation in Fig. 1 has a series of parallel bores. A strip-like insert 10 is positioned in each bore, and the opposite parallel walls of the tube are dimpled at intervals along the length to provide inward projections which offer increased surface for heat conduction and also serve to grip the strip for heat transfer between the strip and the tube. The strip may serve as a turbulator. <IMAGE>

Description

SPECIFICATION Heat exchange tube This invention relates to heat exchange tubes.

GB 2090651B proposes an extruded light alloy tube having passages of substantially square cross section, with the passage walls dimpled alternately along the length of the passage so that inwardly extending dimples form a passage of sinuous shape and of substantially constant cross section along the length of the passage.

GB 2159265A proposes a generally similar tube but with the dimples oppositely aligned instead of being alternate. Hence instead of the passage being of substantially constant cross section but sinuous along its length, each passage consists of a series of chambers located between successive dimples, the chambers being linked by reduced diameter portions between the oppositely aligned dimples.

The constructions described in both of the mentioned patent applications have been found satisfactory for heat exchange purposes.

However, the present invention is based on an improvement applicable to either version, which is found to give substantially higher heat exchange rates with no apparent disadvantages.

According to the present invention, a heat exchange tube comprises at least one bore extending between generally parallel opposite walls of the tube, said walls being dimpled inwardly, and the bore containing one or more longitudinally extending insert which is contacted by said dimples.

Hence, the surface area available for heat exchange is greatly increased: it can be almost doubled by a single strip-like insert, or multiplied by using more than one insert or even by using a single insert of complex cross-section. The dimples can provide good contact between the insert and the tube wall for heat conduction to the tube exterior and heat exchange with a second fluid of the heat exchange pair.

Preferably the invention is utilised with the oppositely dimpled (aligned) version, and the strip is then contacted and gripped at each pair of dimples: in that case, the insert need not be otherwise secured. But if the alternate dimpled version is employed it is preferred to use a brazed, soldered or other fixing construction to ensure good heat conduction.

The inserted strip may be plain, that is to say a simple rectangular cross section foil, preferably of a metal similar to or the same as that used for the heat exchange tube per se, and the transverse dimension may be generally similar to the transverse dimension of the tube bore.

Alternatively, the strip can have apertures, tags struck out of it, notched edges, or be of corrugated shape along its length, or any combination of these features, particularly for the purpose of providing a degree of turbulence or to minmise film effects which can reduce heat exchange efficiency. Further, the strip could be an extrustion of complex crosssection, or a tube: or more than one of these.

The invention is more particularly described with reference to the accompanying drawings in which: Figure 1 is an end elevation of a typical multi-bore tube according to the invention; Figure 2 is a longitudinal section of a portion of a tube according to the invention; and Figure 3 is a view on the line 3-3 of Fig. 2; and Figs. 4 to 9 are fragmentary perspective views showing different insert strips which might be used.

Turning first to Fig. 1, the extruded multibore tube shown therein has ten square bores, but any desired number can be provided and the bores can be of any required cross sectional shape. Each bore is threaded by a strip 10 as further discussed hereinafter.

The strips may be a loose fit in the bores prior to the dimpling operation.

Figure 2 is a sectional elevation taken at the side of one of the passageways, for example on the line 2-2 of Fig. 1. The dimples, in this instance, are aligned opposite one another so that the strip is firmly gripped between each pair of dimples, to provide good heat conduction between the strip and the tube.

The strip illustrated in Figs. 1 to 3 is a plain rectangular cross section metal foil as shown in Fig. 4. Alternative possibilities for strip are as shown in Figs. 5-9 in which Figs. 5 and 9 have the edges of the strip notched which facilitates interflow of fluid from one side of the strip to the other, particularly in cases where the strip is substantially the same in width as the transverse dimension of the bore in which it is inserted. In addition, the edges provide localised turbulence and contribute to what are known in the art as "edge effects" which minimise the disadvantages of film effects.

The strip shown in Fig. 6 is perforated which is thought likely to produce similar results to Figs. 5 and 9.

The strip shown in Fig. 7 has tags struck out of its edges and deflected in different directions, and these are likely to have a greater effect on the turbulence but possibly also cause pressure drop in the fluid flow in the bore.

The strip shown in Fig. 8 may be particularly suitable where the walls of the tube are alternately dimpled, in enabling good heat conduction to be achieved with less work done upon the tube by way of dimples formed in it.

A particularly efficient and cost-effective construction, not shown, will have rectangular bores, several inserts per bore, and possibly also several dimples aligned transversely across each bore. Such an arrangement can give large surface area for heat transfer, effective contact between the strips and tube wall for heat conduction, and low manufacturing costs.

Claims

1. A heat exchange tube comprising at least one bore extending between generally parallel opposite walls of the tube, said walls being dimpled inwardly, and the bore containing one or more longitudinally extending inserts which is contacted by said dimples.

2. A tube as claimed in Claim 1 wherein the insert is a single strip-like insert.

3. A tube as claimed in Claim 1 wherein the bore contains more than one insert.

4. A tube as claimed in Claim 2 wherein the insert is of complex cross-section.

5. A tube as claimed in any preceding claim wherein the tube dimples are oppositely located so that the strip is gripped between each pair of dimples.

6. A tube as claimed in Claim 4 wherein the strip has apertures, tags struck out of it, notched edges, corrugated shape along its length, or any combination of these features.

7. A heat exchange tube substantially as described with reference to Figs. 1-3 and any of Figs. 4-9 of the accompanying drawings.