GB2113375A - Improvements in heat exchangers - Google Patents

Abstract

A heat exchanger comprising a waisted, elongate, sealed jacket (10) having elongate upper and lower bulbous portions (12, 14) above and below the waist (16) and through which upper and lower pipes, respectively 10, 18, extend with clearance. The sealed jacket (10) contains a refrigerant or similar vapourising fluid (22), the liquid phase of which is vapourised by contact with the lower pipe when a heated fluid is passed through, thence to condense on the upper pipe through which a cooler fluid is passed, thereby transferring heat to said cooler fluid, the condensed fluid dropping back to the bottom of the jacket for revapourisation. <IMAGE>

Description

SPECIFICATION Improvements in heat exchangers This invention relates to a heat exchanger, more especially a heat exchanger of the kind used for transferring heat from a first fluid flow to a second fluid flow. In one conventional type of heat exchanger of the kind referred to, the first fluid flow is constrained to pass through an enclosure, and the second fluid flow is confined within a heat-conductive pipe which passes into the exclosure at an externally sealed inlet and exits from the enclosure at an externally sealed outlet. Within the enclosure, the pipe carrying the second fluid flow may be shaped into a tortuous path and/or may carry fins, thereby to increase the surface area available for heat radiation or heat absorption.

Disadvantageously, in this type of heat exchanger, the pipe carrying the second fluid lies in the path of flow of the first fluid and tends to obstruct such flow. This can be especially disadvantageous if the first fluid contains solids, since these are likely to clog and build up around bends in the pipe or around fins thereon.

Other conventional types of heat exchanger are differently arranged, but invariably entail the same disadvantage, which is emphasised in the case of a fluid carrying solids, namely that obstructions extend into the flow passage of at least one if not both of the fluids.

It is an object of this invention to provide a heat exchanger, of the kind referred to, which will operate continuously and efficiently, without deterioration, even if either one or both of the first and second fluids contains clogging solids.

According to the invention, there is provided a heat exchanger which comprises a heat insulated jacket having a sealed internal space for containing fluid, a first pipe for passage of a higher temperature fluid extending through said space in hermetically sealed relationship thereto, a second pipe for passage of a lower temperature fluid extending through said space in hermetically sealed relationship thereto, the second pipe being located at a higher level in said space than the first pipe, and a vapourising fluid contained in said space through which the first and second pipes extend.

In practice the two pipes will extend in parallel relationship, one above the other, and the jacket will be an elongate enclosure surrounding the two pipes along the lengths thereof. Each pipe will enter the jacket through an externally sealed inlet and leave through an externally sealed outlet, thereby to ensure that the jacket is sealed against loss of the vapourising fluid. In practice, the jacket will be evaluated through a suitable valve, which will then be used to enter into the jacket a sufficient quantity of vapourising fluid, in liquid phase, at least partly to cover the lower pipe. Alternatively, a smaller amount of vapourising fluid may be employed, and the lower pipe may have a metal gauze wick depending therefrom, dipping into the liquid phase of the vapourising field. Having entered the vapourising field, the valve may be permanently sealed, if desired.

In use, vapourising fluid evaporates in the region of the lower pipe containing. or passing heated fluid and condenses on the upper pipe containing or passing cooler fluid, whereafter to trickle or drop back to the bottom of the jacket where the higher temperature pipe is located, thence to be re-vapourised. The latent heat taken into the vapourising fluid on evaporation at the heated, lower pipe is transferred to the cooler, upper pipe on condensation, and heat is thus efficiently transferred from the higher temperature fluid to the lower temperature fluid. The jacket is heat insulated to prevent condensation of vapourising fluid on the internal wall surface thereof.

Suitable vapourising fluids are refrigerants such as Freon, alcohols such as methanol, acetones, fluoro-carbons such as carbon tetrafluoride and ammonia. However, any fluid boiling without dissociation in the appropriate temperature range can be employed, provided also that it does not attack or degrade the materials of which the jacket and pipes are made.

A principal advantage of the invention is that the two pipes through which the fluids pass can both be internally formed entirely free of obstructions. The heat exchanger of the invention thus has particular applicability to heat exchange wherein at least one of the two fluids, which will often be the heated fluid, contains solids. Examples of such an application are in the extraction of heat from sewage, domestic effluent, industrial effluent, laundry waste and like waste fluids, whether the latter are primarily liquids, gases or a mixture thereof. However, the heat exchanger of the invention may also be used in other fields such as space heating. In any application, and regardless of whether or not the heated fluid contains solids, the cooler fluid may be a liquid, a gas or mixture thereof which may or may not contain solids.The cooler fluid will preferably be passed in the opposite direction to the heated fluid.

In a preferred embodiment, the jacket has a waisted section at an intermediate level between the levels of the lower and upper pipes.

Especially if it is desirable for the jacket to contain sufficient vapourising liquid fully to cover the lower pipe at all times, as may be necessary if this pipe is passing a very hot fluid, the waisted section enables a lesser quantity of vapourising fluid to be used than would otherwise be the case. Above and be low the waisted section, the jacket will prefer ably be shaped with bulbous tube-like portions through which the respective pipes extend, each with an appropriate clearance all round.

A practical example of heat exchanger in accordance with the invention is shown diagrammatically in the accompanying drawing, in which: the single figure is a perspective view of one possible embodiment.

In the drawing, the reference 10 denotes an elongated heat insulated jacket having tubelike lower and upper sections 1 2 and 1 4 connected by a waisted section 1 6.

A pipe 1 8 containing or passing hot fluid extends through the tube-like bottom section 1 2 of the jacket 10 and a pipe 20 containing or passing cooler fluid in the opposite direction extends through the tube-like top section 14.

The heat insulated jacket 10 is heremtically sealed, and includes local external seals around the inlets and outlets of the two pipes.

Within the jacket 10, which is otherwise evacuated, a vapourising liquid 22 is filled to a level at least partly to cover the lower pipe 1 8. Alternatively, a metal gauze wick depending from the lower pipe 1 8 may dip into a lesser quantity of vapourising liquid 22.

In use, heat transfer from the hot fluid in the lower pipe 1 8 to the cooler fluid in the upper pipe 20 is effected as the vapourising liquid cyclically evaporates at the said lower pipe and condenses at the said upper pipe.

Clearly, the described embodiment may be modified in various ways within the scope of the invention as hereinbefore defined.

Claims (11)

1. A heat exchanger comprising a heat insulated jacket having a sealed internal space for containing fluid, a first pipe for passage of a higher temperature fluid extending through said space in hermetically sealed relationship thereto, a second pipe for passage of a lower temperature fluid extending through said space in hermetically sealed relationship thereto, the second pipe being located at a higher level in said space than the first pipe, and a vapourising fluid contained in said space through which the first and second pipes extend.

2. A heat exchanger as claimed in claim 1, wherein the two pipes extend in parallel relationship, the jacket comprising an elongate enclosure surrounding the two pipes along the lengths thereof.

3. A heat exchanger as claimed in claim 1 or claim 2, wherein the jacket has a valve for evacuation of the jacket and for entry therein of the vapourising fluid.

4. A heat exchanger as claimed in claim 1 or claim 2 or claim 3, containing vapourising fluid in an amount such that the liquid phase of said fluid at least partly covers the lower pipe.

5. A heat exchanger as claimed in claim 1 or claim 2 or claim 3, wherein the lower pipe carries a metal gauze wick depending therefrom, dipping into the liquid phase of the vapourising fluid.

6. A heat exchanger as claimed in any of claims 1 to 5, wherein the vapourising fluid is a refrigerant selected from freon, alcohols, fluoro-carbons and ammonia.

7. A heat exchanger as claimed in any of claims 1 to 6, wherein the jacket has a waisted section at an intermediate level between the levels of the lower and upper pipes.

8. A heat exchanger as claimed in claim 7, wherein the jacket has elongate bulbous portions, above and below the waisted section, through which the respective pipes extend with clearance all round.

9. A heat exchanger substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of heat exchange according to which heated fluid is passed through a lower pipe and cooler fluid is passed through an upper pipe, the pipes are encased by a jacket containing a vapourising fluid, and heat transfer is effected by the cyclic effect of evaporation of the vapourising fluid at the heated, lower pipe, condensation of the vapourised fluid on the cooler, upper pipe, and fall of the condensed fluid back to the heated, lower pipe.

11. A method as claimed in claim 10, wherein the heated fluid is passed through the jacket in the opposite direction to the cooler fluid.

1 2. A method claimed as claimed in claim 10 and claim 11, wherein the heated fluid is a liquid containing solids.

1 3. A method of heat exchange substantially as hereinbefore described.