GB2083604A

GB2083604A - Heat exchanger

Info

Publication number: GB2083604A
Application number: GB8125921A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-10
Filing date: 1981-08-25
Publication date: 1982-03-24
Also published as: DE3135332A1; AU7467281A; FR2489950B3; FR2489950A1; JPS5777887A

Abstract

A heat exchanger comprises three coaxial pipes, that is an inner pipe 2, intermediate pipe 6 and outer pipe 4 defining three passages being an inner passage 18, intermediate passage 16 and outer passage 20. A first fluid passes through the passages 18 and 20 and a second fluid passes through passage 16. <IMAGE>

Description

SPECIFICATION Heat exchanger This invention concerns heat exchangers and especially the tube in tube type commonly found in heat pumps, refrigeration circuits, air conditioners and the like.

U.S. 3199583 describes a tube in tube heat exchanger for cryogenic applications. Efforts to improve the performance of that type of heat exchanger have generally concerned design modifications to maximise exchange efficiency by increases in conductivity, exchange area, thermal gradient, and insulation of the appropriate surfaces.

Optimising the design in this way uses unnecessary masses of expensive metals, the construction of complex manifolds and the use of inserts which increase the risk of corrosion and blockage.

This invention aims to provide a compact exchanger utilising the minimum quantity of metal in return for some improvement in heat exchange ratio.

This invention provides a heat exchanger for a first fluid and a second fluid comprising a trio of thermally conducting pipes of different cross-sectional areas arranged in nested heat exchange relationship which define an inner passage and an outer passage together providing a path for a first fluid, an intermediate passage providing a path for a second fluid, an inlet and outlet in flow connection with the inner and outer passages and an inlet and outlet in flow connection with the intermediate passage. The intermediate passage may be surrounded by the pipe which defines the outer passage. The exchanger may be elongated having two ends, the respective inlets and outlets for the two fluids are located near the ends and the heat exchange is accomplished in a single pass.The cross-sectional areas of the inner passage and the outer passage and the positions of the inlets and outlets may be such as to allow approximately equal flows in both passages. The pipes may be circular cross-section and the ratio of the diameters are in the ratio of about 1.25:1.5:2. Preferably the pipes are coaxially disposed. When the pipes contain a curved portion along their length the intermediate and outer passages may each contain spiral spacers. These are not really necessary in that good alignment can be maintained on even 90" bends by sand filling prior to bending so long as the mutual positions are rendered accurate by fixing the gas inlet and outlet pipes to the outer tube wall. Copper, cupronickel and stainless steel are the metals of choice.This ratio of diameters may not be optimum for heat exchange at a given flow rate and a range somewhat higher and lower than this ratio will also give good results. I have found that in domestic and commercial installations the heat exchangers of this invention are an improvement upon tube in tube exchangers and I fully expect that if the exchanger is scaled up, the same improvement will be evident. For example in an installation for municipal use the ratios of the pipes may require adjustment, so too may the flow rates of the fluid but the improvement is mainly attributable to the exchange efficiency made possible by causing the liquid and gas to contact two curved cylindrical surfaces instead of one. It is expected that flow rates of from 4-8 feet/second will prove useful in heat exchangers of this type for liquids with a specific heat of the same order as water.

One embodiment of the present invention is now described by way of reference to the accompanying drawings in which Fig. 1 is a diagrammatic section ofthe exchanger, Fig. 2 is a section of one end of the exchanger, Fig. 3 is an external view of the same end showing a coupling for hose connection, Fig. 4 is a diagram of its use in a heat pump installation arranged to use a domestic pool as a heat sink/source.

Referring now to Figs. 1 and 2, the exchanger is made of a central round tube 2, 1.0 inches o.d., an outer round tube 4, 2.0 inches o.d. and an intermediate round tube 6, 1.5 inches o.d. All three tubes are made of 18 swg stainless steel. For an installation rated at 2.25 Horsepower, the exchanger is nine feet long. A gas inlet conduit 8 and a gas outlet conduit 10 project through the outer tube 4. The centre tube 2 has a flared portion 12 at each end which is a slide fit in the intermediate tube 6 enabling a circular weld 14 to unite the two tubes forming a gas tight intermediate passage 16. The inner passage 18 and outer passage 20 conduct water th rough the exchanger from water inlet 20 to water outlet 22.Intermediate passage 16 is the condenser of the refrigerant circuit of the heat pump 24 (see Fig. 4). Water flows through the outer and inner passages 20, 18. In order to improve heat exchange in the inner passage a stainless steel spiral 26 is pushed into the mouth of the inner passage to create an initial swirl which persists. This need only extend a short way into the passage. The streams of water thus divide on entry and recombine at outlet 22.

The manner of making the gas inlet and outlet connections are shown in Figs. 2 and 3. Outer tu be 4 has a slot 28 with a semi-circular blind end. The gas inlet conduit 10 abuts the blind end of the slot and is located by the end 30 of a thread sleeve 32 secured to the pipe 4 by a weld 34. The junction of conduit 10 and pipe 4 is sealed by a fillet weld 36. Sleeve 32 receives a male hose coupling 38.

Referring now to Fig. 3, a pump 40 circulates water from a swimming pool 42 through filter 44 and the exchanger which forms part of the domestic heat pump 24. The pump maintains a flow of about 7 ftisecthrough the exchangerwhich is coiled in a spiral inside the heat pump housing. The exchanger collects only sensible heat from the pool water and under steady conditions an input/output ratio of 1:5 is obtainable in contrast to the best performance for a tube in tube exchanger of comparable size of 1:3.

The relevant temperatures are shown below: Gas inlet 1800F Gas outlet 142"F Water inlet 50"F Water outlet 140"F I have found the advantages of this form of heat exchanger to be as follows. The heat exchanger may be constructed with minimal thermal insulation because the hot gas is surrounded by a relatively large volume of moving liquid. The exchanger is cheap to manufacture and may be coiled compactly within the installation the two ends of the coil being joined by a pipe containing a tap whereby the exchanger may be drained of liquid. Large flow rates of liquid are attainable by either installing exchangers in parallel thus bringing further heat pump circuits into the system or by increasing pipe sizes along with the Horsepower rating on the instailation.

Claims

1. A heat exchanger for a first fluid and a second fluid comprising a trio of thermally conducting pipes of different cross-sectional areas arranged in nested heat exchange relationship which define (a) an inner passage and (b) an outer passage together providing a path for a first fluid (c) an intermediate passage providing a path for a second fluid (d) an inlet and outlet in flow connection with the inner and outer passages (e) an inlet and outlet in flow connection with the intermediate passage.

2. A heat exchanger as claimed in claim 1 wherein the intermediate passage is surrounded by the pipe which defines the outer passage.

3. A heat exchanger as claimed in claim 1 wherein the exchanger is elongated having two ends, the respective inlets and outlets for the two fluids are located nearthe ends and the heat exchange is accomplished in a single pass.

4. A heat exchanger as claimed in claim 3 wherein the cross-sectional areas ofthe inner passage and the outer passage and the positions of the inlets and outlets are such as to allow approximately equal flows in both passages.

5. A heat exchanger as claimed in claim 1 wherein the pipes are of circular cross-section and the ratio of the diameters are in the ratio of about

1.25:1.5:2.

6. A heat exchanger as claimed in claim 1 wherein the pipes are coaxially disposed.

7. A heat exchanger as claimed in claim 6 wherein the inner passage is adapted to impart a swirl to the fluid flowing through the passage.

8. A heat exchanger as claimed in claim 6 wherein the inner passage contains a spiral insert capable of imparting a helical direction to the fluid flowing through the inner passage.

9. A heat exchanger as claimed in claim 6 wherein the pipes together form a spiral containing one complete turn.

10. A heat exchanger constructed and arranged to function as herein described and as shown in the drawings.