GB2065861A - Countercurrent heat exchanger with a dimpled membrane - Google Patents

Abstract

A heat exchanger comprises a housing 12, a chamber 14 mounted within the housing and a membrane 16 of dimpled construction connected to either or both the housing and the chamber. The membrane surrounds the chamber and forms a fluid-tight barrier between a first annular zone 18 that extends between the membrane and the chamber and a second annular zone 20 that extends between the membrane and the housing. Inlets and outlets 22i, 22o, 24i and 24o are provided for introducing a first fluid into the first zone and a second fluid into the second zone, and a pressurised plug 28 is mounted within the chamber 14 which has slots 32i, 32i at its ends communicating with the first zone 18. <IMAGE>

Description

SPECIFICATION Heat exchangers with dimpled membrane This invention relates to heat exchangers and, more particularly, to a novel and highly-effective heat exchanger characterised by an improved heat-transfer coefficient, simplicity of construction and ease of cleaning.

Many forms of heat exchangers are known, including heat exchangers employing membranelike metal sheets characterised by various deformations. In the prior art, however, they require heavy hydrostatic support surfaces (plate heat exchangers), cannot readily be disassembled for cleaning, must be operated at low pressure because of lack of support, or require path defining elements. Representative prior patents are United States Patents Nos. 3 705 618, 3 823 458 and 3 854 530.

An object of the invention is to remedy the problems outlined above and, in particular, to provide a heat exchanger including a membrane of special configuration and so constructed that it can be easily disassembled for cleaning, requires no path-defining elements of the type employed in the prior art, and can be operated at high pressure even though the membrane itself is of very light construction.

The foregoing and other objects are attained in accordance with the invention by providing a heat exchanger comprising a housing, a chamber mounted within the housing, and a membrane of dimpled construction connected to at least one of the housing and chamber. The membrane surrounds the chamber and forms a fluid-tight barrier or seal between a first annular zone that extends between the membrane and the chamber and a second annular zone that extends between the membrane and the housing. Means is provided for causing a first fluid to flow through the first zone and for causing a second fluid to flow through the second zone. The two fluids are at different temperatures, whereby heat is exchanged across the membrane.

The invention is preferably characterised by a number of additional features that contribute to its efficient operation. Thus the annular zones have small hydraulic radii that result in an increased Reynolds number. Means is provided for removing at least one of the housing and chamber for cleaning either side of the membrane.

The means for causing the flows of the fluids preferably comprises first inlet and outlet means connected to the chamber, second inlet and outlet means connected to the housing, and plug means mounted within the chamber between the ends thereof. Slot means is formed in the chamber beyond opposite ends of the plug means in order to provide a flow path around the plug means and through the first of the two annular zones mentioned above.

The flow of fluids in the two zones is usually respectively substantially in opposite directions, although other types of flow may be provided for.

Preferably the membrane is formed with a multiplicity of protuberances directed respectively towards the housing and the chamber. The height of the protuberances defines the radial dimensions of the annular zones. The protuberances increase fluid turbulence and thus enhance the heattransfer coefficient. The protuberances are moreover arranged to support the membrane against operating pressures and thus maintain the flow annuli.

A better understanding of the invention may be gained from a consideration of the following detailed description of the preferred embodiment thereof, taken in conjunction with the figures of the accompanying drawings, wherein: Figure 1 is an axial sectional view of the heat exchanger; Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1 and looking in the direction of the arrows; and Figure 3 is a developed view of a membrane that is made from a flat, rectangular sheet and then rolled into the shape of a cylinder or tube of relatively large diameter in order to form a portion of the apparatus of Figures 1 and 2.

The heat exchanger 10 comprises a pressuretight outer tube or housing 12, a hollow inner tube or chamber 14 mounted within the housing 12, and a membrane 1 6 of dimpled construction and made of a material having good thermal and mechanical properties. The housing 12, chamber 14 and membrane 16 are all generally cylindrical and concentric with one another. The membrane in this particular embodiment is located by welds 54 (described below) which connect it to the chamber 14.

The membrane 1 6 substantially surrounds the chamber 14 and forms a fluid-tight barrier or seal between a first annular zone 1 8 that extends between the membrane 1 6 and the chamber 14 and a second annular zone 20 that extends between the membrane 1 6 and the housing 12.

Means 22i, 220, 24i and 240 is provided for introducing a first fluid into the zone 1 8 and a second fluid into the zone 20. The two fluids may be any liquid or gas and may both be water, for example. They are at different temperatures, whereby heat is exchanged across the membrane 1 6, which is formed of stainless steel or.another good conductor of heat. It is within the scope of the invention to make the fluid in the first zone hotter than that in the second, or vice versa.

The annular zones 1 8 and 20 have nearly the same diameter, which means that the annular flow cross-sectional area is small. As a result, these zones have small hydraulic radii, i.e. the cross-sectional area of the flowing fluid divided by the wetted perimeter, which may be only a fraction of an inch or centimetre if the fluids are water. Such small hydraulic radii result in a large Reynolds number that may easily be eight or more times larger than the Reynolds number for a pipe of equivalent circular cross-sectional area.

Means including nuts and bolts 26 is provided for removing end caps 28 of the housing 12, whereby the conduits 22i and 22c and, by virtue of its basically cylindrical shape, the membrane 1 6 may likewise be removed. Alternatively, the housing 12 may be removed, exposing the membrane 16. This permits easy cleaning of the membrane 1 6. Such cleaning is periodically necessary, especially where one of the fluids is, for example, used laundry water, or where high temperatures or corrosion presents a problem.

The means for causing the flows of fluids preferably comprises first inlet and outlet means 22i and 220 connected to the chamber 14, second inlet and outlet means 24i and 240 connected to the housing 12, and plug means 28 mounted within the chamber 14 between the ends 30 thereof.

Slot means 32wand 320 are formed in the chamber 14 on opposite sides of the plug means 28. A flow path is thus established through the conduit 22i as indicated by arrows 34, through the slots 32wand into the first annular zone as indicated by arrows 36, from the first annular zone through the slots 320 as indicated by arrows 38, and through the conduit 220 as indicated by arrows 40.

A flow path is also established through the conduit 24i as indicated by an arrow 42, into the second annular zone as indicated by arrows 44, and from the second annular zone 20 into the conduit 240, as indicated by arrows 46 and 48.

The flows of fluids in the two annular zones 18 and 20 are respectively substantially in opposite directions. The heat exchanger is thus of counterflow type, so that the high-temperature regions of the fluids are at the same end of the heat exchanger 10, and the low-temperature regions of the fluids are at the other end of the heat exchanger. However, it is also within the scope of the invention to establish cross flow and other relative flow directions. For example, the plug 28 and slots 32i, 320 might be replaced by slots distributed circumferentially around the chamber 14, and means for directing flow from inlet 22!two certain of such slots, and for directing flow from the remainder of said slots into outlet 220.

As each of the Figures shows, the membrane 1 6 is formed with a multiplicity of protuberances 50 extending in one direction and 52 extending in the opposite direction. For example, in the assembled heat exchanger, the protuberances 50 may extend in a radially inward direction and the protuberances 52 in a radially outward direction.

Thus the protuberances 50 extend in a direction towards the chamber 14 and the protuberances 52 in a direction towards the housing 1 6.

The height of the protuberances 50, 52 defines the radial dimensions of the annular zones 1 8, 20.

The protuberances 50, 52 may take the form of hemispheres having a radius about equal to the thickness of the sheet metal of which the membrane 1 6 is formed and spaced apart from other hemispheres on the same side of the membranes 16 by 0.5 inch (1.3 cm) and from other hemispheres on the opposite side of the membrane 16 by 0.25 inch (0.65 cm).

The hemispherical protuberances 50, 52 in the membrane 18 may be formed with the aid of a die while the membrane 1 8 is in the form of a flat sheet, as indicated in Figure 3. The sheet is then rolled into cylindrical form and sealed with pressure-tight welds as indicated at 54.

The protuberances 50, 52 increase fluid turbulence and thus enhance the heat-transfer coefficient. The protuberances are moreover arranged to support the membrane 1 6 against operating pressures and thus maintain the flow annuli. They accomplish this by giving the membrane 1 6 additional structural strength because of their curvature, by being in contact with the pressurised fluid on opposite sides thereof, and by bearing against the housing 12 or chamber 14 in case the membrane 1 6 is deformed by unequal pressures on opposite sides thereof.

The membrane 16 is of good thermal properties and maximises heat exchange while minimising the material requirements for a given operating pressure. The membrane 1 6 forms a tube of relatively large diameter, for example 4 inches (10 cm). Since the total hydrostatic load is concentrated at the protuberances 50 52 which are in turn supported by the housing 12 and chamber 14, the membrane can be much thinner than an unsupported tube of equivalent diameter would have to be. Since the housing 12 and chamber 14 are not involved in the heat transfer, they can be made of a variety of materials suitable for resisting hydrostatic loads. In fact, the housing 12, chamber 14 and membrane 1 6 can be made respectively of three different materials.The membrane 16, which is subject to pressure on both sides, and the plug 28, which is hollow and can be permanently pressurised with a gas such as air on the inside, can be made especially light and inexpensive.

The linear tubular construction and counterflow design illustrated preclude the need for pathdefining elements.

Thus there is provided in accordance with the invention a novel and highly-effective heat exchanger characterised by an improved heattransfer coefficient, simplicity of construction and ease of cleaning. Many modifications of the preferred embodiment of the invention disclosed herein will readily occur to those skilled in the art upon a consideration of this disclosure.

Accordingly, the invention is not limited to the specific embodiment disclosed herein but extends to all embodiments thereof that are included within the scope of the appended claims, and to equivalents thereof.

For example, the membrane might be connected to the housing rather than to the chamber, and the connection in any case might be of a releasable kind, enabling the membrane to be removed, and cleaned on both sides.

Claims (12)

1. A heat exchanger comprising a housing, a chamber mounted within the housing, and a membrane of dimpled construction connected to at least one of said housing and chamber, the membrane surrounding the chamber and forming a fluid-tight barrier between a first annular zone that extends between the membrane and the chamber and a second annular zone that extends between the membrane and the housing, and means for causing a first fluid to flow through the first zone and for causing a second fluid to flow through the second zone.

2. A heat exchanger acdording to claim 1, wherein the annular zones have small hydraulic radii that result in an increased Reynolds number as compared with a pipe of equivalent cross sectional area.

3. A heat exchanger according to claim 1 or claim 2, comprising means for removing at least one of said housing and chamber for cleaning at least one side of the membrane.

4. A heat exchanger according to any of claims 1 to 3, wherein the means for causing the flows of the fluids comprises first inlet and outlet means connected to the chamber, second inlet and outlet means connected to the housing, plug means mounted within the chamber between the ends thereof, and slot means formed in the chamber beyond opposite ends of the plug means.

5. A heat exchanger according to claim 4, wherein the plug means is hollow and permanently pressurised on the inside.

6. A heat exchanger according to any of claims 1 to 5, wherein the flow of fluids in said two zones is respectively substantially in opposite directions.

7. A heat exchanger according to any of claims 1 to 6, wherein the housing, chamber and membrane are respectively made of different materials.

8. A heat exchanger according to any of claims 1 to 7, wherein the membrane is formed with a multiplicity of protuberances directed respectively towards the housing and the chamber.

9. A heat exchanger according to claim 8, wherein the height of the protuberances defines the radial dimensions of the annular zones.

10. A heat exchanger according to claim 8 or claim 9, wherein the protuberances increase fluid +urbulence and thus enhance the heat-transfer coefficient.

11. A heat exchanger according to any of claims 8 to 10, wherein the protuberances are arranged to support the membrane against operating pressures and thus maintain the flow annuli.

12. A heat exchanger according to claim 1, substantially as described with reference to the accompanying drawings.