GB2236587A

GB2236587A - Heat exchangers

Info

Publication number: GB2236587A
Application number: GB9015507A
Authority: GB
Inventors: Peter Edward Radford
Original assignee: RADDERS Ltd
Current assignee: RADDERS Ltd
Priority date: 1989-07-18
Filing date: 1990-07-13
Publication date: 1991-04-10
Anticipated expiration: 2010-07-13
Also published as: GB9015507D0; GB8916375D0; GB2236587B

Abstract

A heat exchanger comprises two components (50, 52) which are releasably secured together to define passages for receiving the pipes (76, 78) between which heat exchange is to take place. The components (50, 52) are made from a material with a high thermal conductivity, for example aluminium alloy, and are releasably secured together by screws (83). The heat exchanger also serves as a supporting device for the pipes (76, 78), one of the components (52) being fastened to a mounting surface (8) by bolts (81) and nuts (82). The two components may be pivoted one to the other. The heat exchanger is particularly useful in refrigeration equipment, for enabling heat exchange to take place between refrigerant flowing into and out of an evaporator. <IMAGE>

Description

HEAT EXCHANGERS This invention relates to heat exchangers, and is particularly, although not exclusively, concerned with heat exchangers for use in vapour-compression refrigeration equipment.

It is known to improve the coefficient of performance of a refrigerator by exchanging heat between the liquid inlet and the vapour outlet lines of the evaporator. However, the heat exchangers used for this purpose are expensive to manufacture and fit.

Also, since they require interruption of the pipe circuits, they can provide a potential source of leakage.

According to the present invention there is provided a heat exchanger comprising at least two complementary components of thermally conductive material, which components are connectable together to define longitudinal passages for receiving respective elongate members between which heat exchange is to take place.

In the context of the present invention, the expression "thermally conductive" means having a thermal conductivity of not less than 40W/mK. For most purposes, it is desirable for the thermal. conductivity of the heat exchanger components to be greater than 100W/mK. In a preferred embodiment, the heat exchanger components are made from solid aluminium, or an aluminium alloy.

In many applications, for example where the heat exchanger is used in refrigeration equipment, the elongate members will be pipes for conducting a liquid or vapour. However, the elongate members could, in such applications, take other forms. For example they could be electrical conductors.

For efficient heat exchange, the cross-sectional area of the heat exchanger components should be large relative to the cross-sectional areas of the elongate members between which heat exchange is to take place.

Thus, the shortest distance between the internal surface of each passage and the external surface of the heat exchanger should not be less than half the largest transverse dimension of the passage. For the same reason, the passages should be disposed relatively close to one another, the distance between the passages being less than the shortest distance between the inner surface of each passage and the outer surface of the heat exchanger. Preferably, the distance between the passages is smaller than one tenth of the shortest distance between the inner surface of each passage and the outer surface of the heat exchanger.

In a preferred embodiment, the heat exchange components comprise extrusions of aluminium or aluminium alloy, and consequently have a substantially constant cross-section along their length. In one embodiment, the heat exchanger components may be connected together at a hinge, so that they can be pivoted to an open position, in which the elongate members can be inserted, and subsequently closed to lock the elongate elements in position. The components may, for example, be held in the closed position by releasable fasteners such as nuts and bolts.

In another embodiment, the components may have cooperating flanges disposed on opposite sides of the passages, the respective flanges being secured together by releasable fasteners.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagram of a refrigeration circuit including a heat exchanger; Figure 2 is a perspective view of the heat exchanger; Figure 3 is a sectional view of the heat exchanger; Figure 4 is a sectional view of another embodiment of a heat exchanger, with the components separated; and Figure 5 shows the heat exchanger of Figure 4 assembled over two pipes.

By way of example, the purpose of the refrigeration circuit shown in Figure 1 is to maintain a low temperature in a cold space 2, which may be a cold cabinet for the retail display of produce in a supermarket. The circuit comprises an evaporator 4 disposed within the cold space 2. Refrigerant passes, as a liquid, from a reservoir 6 through a heat exchanger 8 to a throttle valve 10. The refrigerant vaporises as it leaves the throttle valve 10 and passes into the evaporator 4, drawing heat from the cold space 2 as it does so. Vaporisation may, however, be incomplete, particularly if the temperature in the cold space 2 has reached its minimum level, and the vapour leaving the evaporator may therefore contain some liquid refrigerant. From the evaporator 4, the refrigerant passes through the heat exchanger 8 to a compressor 12, which may be in the form of a reciprocating piston pump.The compressed refrigerant is delivered by the pump to a condensor 14 in which the refrigerant condenses, to be returned in liquid form to the reservoir 6.

The liquid refrigerant passing through the heat exchanger from the reservoir 6 to the throttle valve 10 is at a higher temperature than the vapour passing through the heat exchanger from the evaporator 4 to the compressor 12. The vapour passing from the evaporator is thus heated, and its enthalpy rises. There is a corresponding decrease in the enthalpy of the liquid refrigerant flowing through the heat exchanger 8.

The increase in enthalpy of the vapour reaching the compressor 12 ensures that any liquid refrigerant which is present is vaporised before it reaches the compressor. Also, the reduction in enthalpy of the refrigerant reaching the evaporator 4 from the throttle valve 10 increases the refrigeration effect, and so increases the coefficient of performance of the cycle.

The heat exchanger 8 is shown in greater detail in Figures 2 and 3. As shown in Figure 2, the heat exchanger is fitted over two pipes 16 and 18 which comprise, respectively, the pipe leading from the evaporator 4 to the compressor 12 and the pipe leading from the reservoir 6 to the throttle valve 10. It will be appreciated that, because the pipe 18 conveys liquid refrigerant, while the pipe 16 conveys refrigerant vapour, the pipe 16 will have a greater diameter than pipe 18.

The heat exchanger 8 comprises two components 20, 22 which are each formed by cutting an aluminium extrusion-to the appropriate length. The components 20 and 22 are interconnected at a hinge 24, and are secured together over the pipes 16 and 18 by nuts and bolts 26 passing through holes drilled in flanges 28 of the components.

As shown in more detail in Figure 3, the components 20 and 22 define between them passages 30, 32 for receiving the pipes 16 and 18 respectively. The passages 30, 32 are formed so as to make intimate contact with the pipes 16 and 18 to ensure good heat transfer around substantially the entire periphery of the pipes 16 and 18. For the same reason, the passages 30 and 32 are disposed close to each other, the recesses in the components 20 and 22 which define the passages 30 and 32 being connected to each other by short transition surfaces 34 and 36.The transition surface 34 is parallel to the plane 38 containing the longitudinal axes of the passages 30 and 32, but the transition surface 36 is inclined to this plane at an angle of 19.50, and instead extends radially with respect to the longitudinal axis-of the passage 32, in order to assist insertion of the pipe 18 when the components 20, 22 are hinged to the fully open position, while retaining the maximum amount of material between the pipes. Also, the adjacent surfaces 40 of the flanges 28 extend obliquely, at an angle of 40, to the plane 38, to assist the drainage of any water which may have condensed on the exposed surfaces.

The hinge 24 is formed by cooperation between a groove 42 of arcuate cross-section, provided in the component 20, and a rib 44, of complementary arcuate cross-section, formed on the component 22. The rib 44 may be a snap fit in the groove 42, but alternatively the components 20 and 22 may be assembled by sliding the rib 44 axially into the groove 42.

The maximum opening angle of the two components 20 and 22 is limited by opposed faces 46, formed on the two components.

It will be appreciated from Figure 3 that the thickness of the material of the components 20 and 22 (i.e. the minimum distance between the surface of the passages 30 and 32 and the outer periphery 48 of the components) is large relatively to the diameters of the passages 30 and 32 themselves. In the illustrated embodiment, this dimension is greater than the diameter of the larger passage 30. Also, the distance between the passages 30 and 32 is small, and as illustrated is approximately one twentieth of the smallest distance between the inner surface of the passage 30 and the periphery 48. Another significant feature is that, apart from the gap between the transition surfaces 34 and 36, the material of the components 20 and 22 is continuous between the passages 30 and 32.Thus, the path of thermal conduction between the pipes 16 and 18 within thq passages 30 and 32 is kept as small as possible to enhance the transfer of heat between the pipes.

To install the heat exchanger of Figures 2 and 3 in a refrigeration circuit, it is necessary to ensure that the sizes of the pipes 16 and 18, and the spacing between them, conforms to the passages 30 and 32. The components 20 and 22 are fitted together at the hinge 24, and are opened to enable the heat exchanger to be fitted over the pipes 16 and 18. The components 20 and 22 are then closed over the pipes and secured firmly in position by means of the nuts and bolts 26. If desired, one or more of the nuts and bolts 26 can be used to secure the heat exchanger to a suitable support, for example to the body of the refrigerated cabinet.

Because the heat exchanger can be installed without needing to break the pipes 16 and 18, and consequently without any need to make a liquid-tight joint, the possibility of causing a leak by the fitting of the heat exchanger 8 is minimised. Furthermore, the fitting and removal of the heat exchanger can be accomplished very quickly.

By way of specific example, where the diameters of the refrigerant pipes are 3/8" (9.53mm) and 5/8" (15.8mm), a significant improvement in the coefficient of performance of a refrigerated cabinet can be achieved using a heat exchanger as shown in Figures 2 and 3 with a longitudinal dimension (parallel to the direction.of the pipes 16 and 18) of 250 millimetres and with a wall thickness of the components 20 and 22 (i.e. the distance between the surface of the passage 30 and the outer periphery 38) of approximately 20 millimetres.

Of course, heat exchangers in accordance with the present invention will need to be available in various sizes to suit different diameters of refrigerant pipes.

Commonly used pipe sizes are 3/8" and 5/8" (9.53mm and 15.88mm), 1/2" and 7/8" (12.70mm and 22.23mm), 5/8" and 1/8" (15.88mm and 28.58mm), and 7/8" and 3/8" (22.23mm and 34.93).

Figures 4 and 5 show another embodiment of heat exchanger. As with the previous embodiment, the embodiment shown in Figures 4 and 5 comprises two components 50, 52 which comprise cut lengths of solid aluminium extrusions. The component 50 has a main body 54 provided with semi cylindrical recesses 56 and 58 which are situated between two grooves 60. On each side of the main body 54 there is a flange 62.

The component 52 also has a main body 64, provided with semi cylindrical recesses 66 and 68. On opposite sides of the recesses 66 and 68, there are projections 70 which are complementary in shape to the grooves 60.

Flanges 72 extend from opposite sides of the main body 64. A channel 74 is provided along one face of each flange 72.

Figure 5 shows the heat exchanger secured over two pipes 76 and 78, and mounted on a panel 80 of, for example, a refrigerated cabinet. The projections 70 cooperate with the grooves 60 to locate the components 50 and 52 securely relatively to each other. The recesses 56, 66 and 58, 68, respectively form passages receiving the pipes 76 and 78, ensuring good thermal contact between the components 50 and 52 and the pipes 76 and 78 around substantially the entire circumference of each pipe.

The components 50 and 52 are secured together and to the panel 80, by nuts and bolts 82. In order to achieve a stable seating of the heat exchanger against the panel 80, the flanges 72 and the main body 64 of the component 52 are provided with mutually coplanar contact surfaces 84.

It will be noted that the spacing between the pipes 76 and 78 is very small relatively to the diameters of these pipes, and that the gap between the pipes is occupied entirely by the material of the components 50 and 52. Also, the shortest distance from each pipe'76 or 78 to the external surface of the heat exchanger is greater than half the diameter of each pipe and, in the case of the pipe 78, greater than the whole diameter of the pipe.

To install the heat exchanger, the component 52 is first secured to the panel 80 using countersunk bolts 81 extending through pre-drilled holes in the component 52, and fastened by nuts 82. The heads of the bolts 81 are received in the channels 74.

The pipes 76 and 78 are then fitted into the recesses 66 and 68, and then the component 50 is fitted to the component 52 and secured using self-tapping screws 83 The screws 83 are offset from the bolts 81 along the heat exchanger, and extend through predrilled hdles in the flanges 62 and across the channels 74 into the material of the component 52.

As with the embodiment of Figures 2 and 3, an effective heat exchanger for use with refrigerant pipes having diameters of 3/8 inch (9.53 mm) and 5/8 inch (15.8 mm) may have a length (parallel to the pipes 76 and 78) of 250 mm and a main body (comprising the main bodies 54 and 64 of the components 50 and 52) having dimensions of approximately 45 mm x 35 mm.

Although the invention has been described with particular reference to heat exchange, it will be appreciated that it also provides a convenient means for simply clamping and mounting pipes. If no heat exchange between the pipes is required, the components need not be made from a material which is a good conductor of heat. For example they may be made from plastics material.

Claims

1. A heat exchanger comprising at least two complementary components of thermally conductive material, which components are connectable together to define longitudinal passages for receiving respective elongate members between which heat exchange is to take place.

2. A heat exchanger as claimed in claim 1, in which the thermally conductive material has a thermal conductivity of not less than 40 W/mK.

3. A heat exchanger as claimed in claim 2, in which the thermally conductive material has a thermal conductivity of not less than 100 W/mK.

4. A heat exchanger as claimed in any one of the preceding claims, in which the thermally conductive material is aluminium or an alloy of aluminium.

5. A heat exchanger as claimed in any one of the preceding claims, in which the components comprise extrusions of the thermally conductive material.

6. A heat exchanger as claimed in any one of the preceding claims, in which the passages have different cross-sectional dimensions from each other.

7. A heat exchanger as claimed in any one of the preceding claims, in which the passages each have a circular cross-section.

8. A heat exchanger as claimed in any one of the preceding claims, in which the components are connected together at a hinge for pivotal movement relatively to each other about an axis parallel to the passages.

9. A heat exchanger as claimed in any one of the preceding claims, in which the components have respective flanges which receive fastening means for securing the components together.

10. A heat exchanger as claimed in claim 9, in which each component has two of the respective flanges, disposed on opposite sides of the longitudinal passages, for securing the components together.

11. A heat exchanger as claimed in any one of the prece ding 'claims, in which the components have complementary locating means for locating the components relatively to each other.

12. A heat exchanger as claimed in any one of the preceding claims, comprising first retaining means for securing one of the components to a mounting surface, and second retaining means for securing the other component to the said one component.

13. A heat exchanger substantially as described herein with reference to, and as shown in, Figures 2 and 3 or Figures 4 and 5 of the accompanying drawings.

14. Refrigeration equipment including a heat exchanger in accordance with any one of the preceding claims.