GB2039021A - Baffle arrangement for guiding fluid flow in tubular heat exchangers - Google Patents

Abstract

In a tubular heat exchanger, fluid e.g. water is contrained to flow crosswise over the tubes (3) by means of involute-shaped baffles or partitions (10) which define a series of transversely extending flow passages (9) of substantially the same cross- section. <IMAGE>

Description

SPECIFICATION A fluid-flow arrangement for ring, polygonal and similar heat exchangers.

The present invention relates to a fluid-flow arrangement having channels of at least substantially the same cross sectional area for ring heat exchangers, polygon heat exchangers or ring parts or polygon part heat exchangers of the socalled gas tube heat exchanger type.

In the case of such heat exchangers it is advantageous if the heat exchange fluid flows in channels of equal width in order to obtain a uniform flow velocity.

There are known ring heat exchangers or ring part heat exchangers where the tubes forming the tube nest are of different cross sectional area so that wider tubes are used on the outer periphery. It has also been proposed to form radial channels so that tube bundles of rectangular cross section are provided which, while of the same size, are arranged small end up in the inner ring rows and wide side up in the outer ring rows. The flow of the heat exchange fluid in radial channels, however, has a drawback in that the existing heat transfer surface is not fully utilized so that a heat exchanger of this type invariably has to have a larger heat exchange surface than would actually be needed to transfer a given heat flux.

An object of the present invention is to provide heat transfer fluid flow so that the transfer of a given heat flux is possible with a minimum of heat transfer surface while maintaining an at least approximately constant fluid flow velocity.

The invention provides a fluid-flow arrangement for a heat exchanger and comprising a plurality of iongitudinally-extending gas tubes and fluid-flow passages of the same cross section extending transversely to the tubes, wherein the passages are bounded by walls extending in a plane transverse to the longitudinal axis of the tubes and each being formed substantially in the shape of an involute.

Manufacturing costs are reduced if the walls of the passages are formed by members having the same profile shape over their full depth and extending the full depth of the arrangement, the members being sealingly connected adjacent to each other to form the wall and having the same cross-sectional shape as the ends of the tubes.

Preferably the members are tubes, e.g. tubes which are open at their ends. This is an advantage, especially inasmuch as the weight is reduced.

Moreover, the inlet losses (compared with conventional gas tube heat exchangers with tube ends expanded typically to form a hexagon) are not increased.

Embodiments of the invention will now be described with reference to the accompanying drawing, in which Fig. 1 is a plan view of a heat exchanger element with heat exchange fluid pipes on its outside, Fig. 2 is a section taken along the line Il-Il of Fig, 1, Fig. 3 is a plan view of another heat exchanger element with heat exchange fluid admission and discharge on its outside, Fig. 4 is a plan view of a heat exchanger element with heat exchange fluid admission and discharge inside, Fig. 5 is a plan view of another heat exchanger element with heat exchange fluid admission and discharge inside and Fig. 6 is a detail shown by perspective representation.

In Figs. 1 and 2, a heat exchanger has a pressure-tight shell 1 having connections 2 for an inlet 2a and a discharge 2b of the heat exchange fluid, e.g. water. Arranged inside the shell 1 is a tube bank having an outer contour in the shape of a regular dodecagon. The tube bank is formed by vertical, straight, parallel, non-finned gas-carrying tubes 3, which are only partly shown in Fig. 1. By "non-finned" is to be understood that the pipes have no ribs increasing the heat-transferring surface but possibly are provided with circumferential beads or similar devices to induce turbulence. The tubes 3 are preferably round tubes which have only their two ends expanded radially, preferably to form a hexagon, and in the region of the adjoining hexagon faces are bonded together so as to provide a tight seal for the heat transfer fluid.The shell 1, viewed in cross section, i.e. in a direction perpendicular to the air flow 4 and to the longitudinal axis of the tubes 3, is circular. The heat exchanger has a transverse partition 5 substantially midway between its ends and extending across the longitudinal axis of the tubes 3. The partition 5 does not quite completely cover the cross-sectional area of the shell so that a twopass type flow pattern is achieved within the heat exchanger, i.e. the heat exchange fluid is admitted through the inlets 2a to flow through the upper half 6a of the heat exchanger whereupon it is deflected through 1800, flows then through the lower half 6b of the heat exchanger to leave the heat exchanger through the outlets 2b.

The admission and discharge of the heat exchange fluid to and from the tube bank is effected at three sides of the regular dodecagon, i.e. at sides 7a, 7e and 7i (Fig. 2). The heat exchange fluid which envelopes the circular tubes 3 on their outside is made to flow in three sections 8a, 8b, 8c in passages 9 of identical cross section across the longitudinal axis of the tubes 3 through the heat exchanger. The boundaries of the passages 9 (seen in a section across the longitudinal axis of the tubes 3) have a shape approximating to that of an involute.

The partition 10, substantially in the form of an involute, forms part of the boundary of the passages 9 between the sections 8a, 8c and is formed from four straight adjoining wall parts 1 Oa to 1 Od, which extend the full depth of the heat exchanger and start from the edge c of the regular dodecagon centre of the heat exchanger.

Similarly, the partitions 11, 12 each approximating to an involute and each comprising a wall formed by four planar sections, start at the edges g and k respectively of the dodecagon and similarly terminate at the centre of the heat exchanger so that the partitions 10, 11 and 12 all meet at the centre of the heat exchanger.

Extending between the partitions 10 to 12, there are additional channel walls 13, 14 and 15 each approximating to the shape of an involute.

The channel walls 13 to 1 5 are formed by the planar wall sections extending the depth of the heat exchanger ( 1 13b, 13c; 14a, 14b, 14c; 15a,15b,15c). The channel wall 13 starts at the edge a and extends inwards between the partitions 10 and 1 2 to terminate at a distance from the wall 1 Od of the partition 10 corresponding to the channel width so that two flow channels of equal cross section are formed in the corresponding flow section 8c.The heat exchange fluid is admitted in the upper region of the heat exchanger through the inlet 2a at the side 7a to flow through the channel of constant cross section formed by the partitions 10, 13, from the outside towards the inside, where it is deflected to flow through the channel of constant cross section formed by the partitions 12 and 13 from the inside towards the outside. The fluid then flows at the periphery from the upper half 6a through an angle of 1800 into the lower half 6b of the heat exchanger, flowing through the channel formed by the partitions 12, 1 3 from the outside towards the inside, is deflected inside and flows through the channel formed by the partitions 10, 13 towards the outside to leave the exchanger through the lower outlet 2b.

Similarly, the channels walls 14 and 1 5 extend between the partitions 10, 11 and 11, 12 respectively starting at the edges e and itowards the inside to end a distance corresponding to the channel width from the planar wall sections 11 d, 1 2d of the partitions 11 and 12. The channel walls 14 and 1 5 are also arranged so that a continuous channel of equal cross section is formed in each sector and in each heat exchanger half.

The channels 9 need not be bounded over their full length by wall sections. For instance, the radially-innermost wall sections 10d, 1 1 d, 12dof the channel walls 10 to 12 may be omitted if the design is such that a uniform pressure exists at the centre of the heat exchanger. In this case, a connecting chamber is formed as it were in the interior of the heat exchanger (Fig. 3).

In the embodiment of Fig. 4, the heat exchanger (seen in transverse section perpendicular to the longitudinal axis of the tubes 3) is formed with a tube bank outer contour in the shape of a regular hexagon. In the inside of the heat exchanger, there is a space where there are no air-carrying tubes 3 so that a fluid chamber 16 is formed extending the full depth of the heat exchanger for the admission and discharge of the heat transfer fluid. The chamber 1 6 is bounded by tubes arranged so that planar inner surfaces of a hexagon result. A straight dividing line (inner plane) can be obtained if the circular tubes there are expanded at their ends to give them a pentagonal shape.

The heat exchanger is also formed with a corresponding partition at its centre which extends through the chamber 16 in the region outside the perpendicular pipes so that a heat exchanger having upper and lower fluid-carrying halves is obtained. Heat exchange fluid is admitted to the upper half of the heat exchanger through the chamber 1 6. The heat exchange fluid leaves the heat exchanger through its lower half.

The heat exchange fluid flows through channels 9 of equal cross section in the upper half front the inside outwards and, after 1 800 deflection, it flows from the outside towards the inside in the lower half through corresponding channels of equal cross section. The boundaries of the channels, seen transversely to the longitudinal axis of the tubes 3, are of involute shape, with the involute 10' each starting at the edge of the inner hexagon and terminating at the outer edges of the outer hexagon.

The walls of involute shape or of a shape approximating thereto are formed in a straightforward manner by sectional members 23 (Fig. 6) which extend the full depth of the heat exchanger element and have the same cross-sectional shape over their full length, i.e. the cross-sectional shape which is used for the expanded ends of the circular tubes 3. If the circular tubes 3 are expanded at their ends to form a hexagon, then the sectional members 23 also are of hexagonal shape. The adjacent hexagonal sections are in contact with each other so that they form a relatively tight seal for the channels 9.

The sectional members 23 may be hollow or solid (this configuration of the channel boundaries applies to all embodiments illustrated).

The shape of the shell 1 (seen in section perpendicular to the longitudinal axis of the tubes 3) may be either round, e.g. circular, or n-angular, with n to be chosen greater than 4. The crosssectional shape of the tubes 3 is optional. This, too, applies to all embodiments illustrated.

In the embodiment of Fig. 5, a heat exchanger element 1 7 has an outer contour 18 (seen in section perpendicular to the longitudinal axis of the circular tubes 3) of a regular hexagon. The centre of the heat exchanger element is free from any circular tubes 3 and the chamber 19 so formed, which extends the full depth of the heat exchanger element, also has a boundary formed by the circular tubes 3 which, similarly seen in section transverse to the longitudinal axis of the circular tubes, is of hexagonal shape. The chamber 1 9 serves to admit and discharge the heat exchange fluid. The circular tubes 3 are formed exactly as in the previous embodiments described.

The heat exchanger element also has one or several partitions in planes perpendicular to the longitudinal axis of the circular tubes in order to form a "multi-pass" heat exchanger element.

The heat exchange fluid admitted through the chamber 19 flows through channels 20 of equal cross section in the upper heat exchanger half from the inside towards the outside where it is deflected (assuming there is only one partition) into the lower heat exchanger half reversed through 180 to flow through the channels 20 from the outside towards the inside. The boundaries of the channels 20 (seen in a plane perpendicular to the longitudinal axis of the circular tubes 3) are formed with the approximate shape of an involute.The channel boundaries are each formed by five plane wall sections 21 a to 21 e extending the full depth of the element. the channel boundaries start at the edges of the inner hexagon and extend in the shape of involutes towards the outside with the last wall sections 21e forming the greater part of the outer contour 18 of the heat exchanger element. The outer contour 1 8, at the point where the passages end (at 22) have no partition but only the usual circular tubes. At the outside of the hexagon, there are further identical heat exchanger elements (not shown. Adjoining the heat exchanger elements in the region of the expanded ends of the tubes are connected at 22 through intermediate members permitting expansion and/or contraction (not shown).

The physical construction of the wall sections 21 is exactly the same as previously described in conjunction with the first embodiment (Figs. 1 and 2).

The fluid flowing longitudinally through the circular tubes 3 may be air or any other gas.

The tubes 3, irrespective of their distance from the centre of the heat exchanger (apart from filling pipes that may be provided at the periphery) are formed with the same cross-sectional shape and the same cross-sectional area.

The term heat exchanger element (heat exchanger part) is intended to include an element which in turn consists of elements, which, for instance, may be formed as shown in Fig. 5. The individual elements would then have no pressuretight boundaries but only the outer boundary of the complete heat exchanger element would be surrounded by a pressure-tight shell.

Claims (8)

1. A fluid-flow arrangement for a heat exchanger and comprising a plurality of longitudinally-extending gas tubes and fluid-flow passages of the same cross section extending transversely to the tubes, wherein the passages are bounded by walls extending in a plane transverse to the longitudinal axis of the tubes and each being formed substantially in the shape of an involute.

2. A fluid-flow arrangement as claimed in claim 1 , wherein the substantially involute shaped walls of the passages are formed from planar wall sections.

3. A fluid-flow arrangement as claimed in claim 1, wherein the passage walls are formed by the surfaces of members extending over the full depth of the arrangement and having the same surface shape over their full depth, the members being tightly connected adjacent to each other and having the same cross-sectional shape as the ends of the tubes.

4. A fluid-flow arrangement as claimed in claim 3, wherein the cross-sectional shape of the tubes and the wall members is hexagonal.

5. A fluid-flow arrangement as claimed in claim 3, or 4, wherein the wall members are tubes.

6. A fluid-flow arrangement as claimed in claim 5, wherein the wall member tubes are open ended.

7. A fluid-flow arrangement substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.

8. A heat exchange having at least one fluidflow arrangement as claimed in any one of the preceding claims.