HEAT EXCHANGER

TECHNICAL FIELD OF INVENTION

This invention relates to a heat exchanger which facilitates the transfer of heat from a heat transfer fluid flowing in a tube to a flat or curved surface and vice versa. The heat exchanger also can be used in the simultaneously heat transfer between a plurality of mediums.

BACKGROUND OF INVENTION Environment conservation concern and the hike in energy costs lately have generated very strong interests in energy conservation. In one prior art, rejected heat generated from heat pump, air-conditioning system, refrigeration system and the like is utilized in heating up water for domestic or commercial use. Fig. 5 shows a prior art of a water heating apparatus (5) adopting such energy conservation concept. The water heating apparatus (5) has a water storage tank having a cylindrical body (51) between top and bottom covers (52 and 53) with a spaced apart water inlet and outlet pipes (54 and 55) at the top cover (52) to pipe in cold water for heating up and to pipe out heated up hot water from the water storage tank. The top cover (52) has an opening with a connector (59) fixed thereto through which a heat exchange coil (50) can be inserted into the water tank and tightened in place to the connector (59) with a hexagonal fastening device (58). Heat laden heat transfer fluid from say an air- conditioning system flows into the heat exchange coil (50) in the water storage tank via a heat transfer fluid inlet pipe (56) and out through a heat transfer fluid outlet pipe (57). In the process, heat carried in the heat transfer fluid heats up water in the water storage tank. The water heating apparatus (5) of this prior art has several disadvantages. Firstly, the coil (50) needs to be made from corrosive resistant materials, inclusive of resistant against chlorine in the water. These corrosive resistant materials include copper, titanium and stainless steel, all of which has gone up substantially in price lately. Secondly, if there is a leakage of heat transfer fluid in the coil (50), the entire water distribution system would be contaminated. Thirdly, the water storage tank would need to provide for an opening together with the connector (59) and the hexagonal fastening device (58). These shortcomings could be overcome if the heat exchange coil (50) could be replaced with a heat exchanger located outside the water storage tank. The heat exchanger can then be made from much cheaper

material such as aluminium which is one seventh the costs of copper and at the same time a water storage tank without the opening, connector and hexagonal fastening device is easier to manufacture, lowering the manufacturing cost of the water storage tank. In another prior art, the heat exchange coil (50) in Fig. 5 is replaced with a tubular electric heating element. Again the tubular electric heating element must be enclosed within a tube made of corrosive resistant material.

To overcome the disadvantages of water heating apparatus of the prior art, it is desirable to have a heat exchanger that could be placed outside the water storage tank to heat up water in the storage tank of the water heating apparatus from outside. Apart from overcoming the aforesaid disadvantages, other advantages are apparent. For instance in the case of an air-conditioning water heaters, in the event of leakages in the refrigerant and oil, the water would not be contaminated. In addition, when serving the water heating apparatus in changing the heating element or heat exchange coil, the water in the water storage tank do not need to be drained if the heating element or coil is located outside the storage tank. However there are no specific heat exchangers available for the transfer of heat from a tube to a flat or curved surface and vice versa.

In this case, it is the transfer of heat from the heat transfer fluid flowing through a tube to a flat or curved surface or the transfer of heat from a tubular electric heating element to a flat or curved surface. The contact surface between a tube and a flat or curved surface is limited to the line defined by the loci of the tangential points where the tube meets the flat or curved surface, resulting in low heat transfer rate from the tube to the flat or curved surface and vice versa. There is accordingly a need to provide a device that could facilitate transfer of heat from the heat transfer fluid flowing through a tube to a flat or curved surface or the transfer of heat from a tubular electric heating element to a flat or curved surface. Again, the contact surface between a tube and a curved surface is limited to the line defined by the loci of the tangential points where the coiled tube or tubular electric heating element meets the curved surface.

In addition, in the case where a tube or a tubular electric heating element, as the case may be, is coiled around a curved surface to secure contacts between the tube or the tubular electric heating element and the curved surface, the tube or the tubular electric heating element will usually have to be welded or brazed to the flat surface or

curved surface, which is a tedious and expensive process. Alternatively the tube is bonded to the flat or curved surface with a heat conducting cement. In this latter case, the thermal bond is usually unsatisfactory.

In view of the forgoing, it is an objective of the present invention to provide a heat exchanger that could more efficiently transfer heat between a tube and a flat or curved surface.

In particular, the heat exchanger of this invention finds applications in energy saving water heating technology involving heat pump and waste heat recovery from air conditioning system. The heat exchanger of this invention also finds applications and in the manufacture of refrigerators, freezers, solar panel water heaters and electric storage water heaters.

SUMMARY OF INVENTION

The invention relates to a heat exchanger which facilitates the transfer of heat from a heat transfer fluid flowing in a tube to a flat or curved surface and vice versa.

In one embodiment of the invention, the heat exchanger comprises an integral piece of metal having at least one tube with the or each of the tubes integrally connected longitudinally to the top surface of a bar and with the bottom surface of the bar in good thermal contact with the flat or curved surface where heat is to be transferred onto from the heat transfer fluid flowing there through the or each of the tubes of the heat exchanger.

In another embodiment of the invention, the heat exchanger comprises an integral piece of metal having at least a pair of wings, with the or each pair of wings integrally connected longitudinally to the top surface of a bar and with the wings joined to each other at the end where the wings meets the bar and rising from the top surface of the bar, forming a substantially U-shaped channel between each pair of wings. In this embodiment, a tube or a tubular electric heating element may be circumferentially enclosed in a chamber formed by pressing the pair of wings towards one another when the tube or the tubular electric heating element is placed in the substantially U-shaped channel.

The heat exchanger of this invention can have numerous possible combinations of tubes and wings integrally connected to the bars to transfer heat between a plurality of mediums to or from a flat or curved surface.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 and Fig. Ia show a cross section of an embodiment of a heat exchanger of the present invention;

Fig. Ib is a three dimension view, with truncated length, of the heat exchanger as shown in Fig. 1 ;

Fig. 2 and Fig. 2a show the cross section of another embodiment of a heat exchanger of the present invention;

Fig. 2b is a three dimensional view, with truncated length, of the heat exchanger as shown in Fig. 2; Fig. 2c shows cross sectional view of the heat exchanger of Fig. 2 with a tubular electric heating element circumferentially enclosed therein;

Fig. 2d is a three dimensional view, with truncated length, of the heat exchanger with a tubular electric heating element circumferentially enclosed therein as shown in Fig. 2c. Fig. 3 is a cross sectional view illustrating one possible configuration of a heat exchanger with a combination of heat exchangers as illustrated in Fig. 1 and Fig. 2;

Fig. 4 is a cross sectional view illustrating another possible configuration of a heat exchanger with a combination of heat exchangers as illustrated in Fig. 1 and Fig. 2; Fig. 5 shows a water heating apparatus of the prior art suitable for use in waste heat recovery;

Fig. 6 shows the use of heat exchanger of Fig. 1 in water heating apparatus; Fig. 7 shows a heat exchanger of Fig. 2 with the heat exchanger having tubular electric heating elements circumferentially enclosed in the chambers; Fig. 8 shows the use of the heat exchanger with tubular electric heating elements circumferentially enclosed in the chambers, as shown in Fig. 7, in a water heating apparatus.

DETAILED DESCRIPTION OF INVENTION Referring to Figs. 1 and Ib, in one embodiment of the heat exchanger of this invention, the heat exchanger (1) comprises an integral piece of metal having a tube (11) and a bar (12) having a top and bottom surfaces (17 and 18) with the tube (11) integrally connected longitudinally to the top surface (17) of the bar (12). The tube (11) allows a heat transfer fluid to flow there through. In use, the bottom surface (18)

of the bar (12) is placed in contact with a flat or curved surface such that the bottom surface (18) of the bar (12) is in good thermal contact with the flat or curved surface onto which heat exchange is to be effected between the heat transfer fluid flowing through the tube (11) and the flat or curved surface. The bar (12) greatly increases the contact surface between the heat exchanger and the flat or curved surface, thereby increasing the contact surfaces for heat transfer or exchange which otherwise will only be limited to a line contact defined by the loci of the tangential points where a tube meets the flat surface or curved surface. Since the heat exchanger is not in contact with water, aluminium or its alloys, which otherwise is attacked by chlorine in water can be used as the material for the manufacture of the heat exchanger. One advantage of aluminium or its alloys is that it costs only one seventh the price of copper. Further, articles of aluminium lend itself readily to manufacturing through an extrusion process, enabling different profiles to be manufactured cost effectively. Aluminium or tis alloys is relatively softer and therefore the heat exchanger of this invention could be coiled readily around a curved surface to facilitate heat transfer between heat transfer fluid following through the tube (11) of the heat exchanger (1) to a flat or curved surface.

Preferably, the tube (11) is symmetrically located along the longitudinal axis of the bar (12) for balanced heat transfer from the tube (11) to the bar (12) on either side of the tube (11). Preferably the cross section of the tube (11) is substantially circular in shape, although the extrusion process enables tube of other shape such as elliptical cross section to be manufactured equally readily. For ease of manufacture and for effective heat transfer, the tubes (11) and the bar (12) of the heat exchanger (1) are substantially of the same length. Fig. Ia shows a heat exchanger (1) of this invention where the bar (12) tapers off gradually at both the longitudinal edges (19) to maximize contact surface with the flat or curved surface and for esthetic reason.

Although Figs. 1 and Ia show only one tube (11) integrally connected to the bar (12), the heat exchanger (1) could have a plurality of tubes (11) connected to bar (12).

Fig. 6 shows an example of an application of the heat exchanger (1) as illustrated in Fig. 1. In this example, the heat exchanger (1) is used to transfer heat to a storage tank of a water heating apparatus (6). The water heating apparatus (6) comprises the heat exchanger (1) and a water storage tank of metal, the water storage

tank has a cylindrical body (61) between top and bottom covers (62 and 63) with a spaced apart water inlet and outlet pipes (64 and 65) at the top cover (62). In this example the heat exchanger (1) is coiled firmly and tightly around the external surface of the cylindrical body (61) of the water storage tank in a helical or spiral manner such that the bottom surface (18) of the bar (12) of the heat exchanger (1) is in good thermal contact with the external surface of the cylindrical body (61) of the water storage tank to facilitate transfer of heat from heat transfer fluid flowing through the tube (11) of the heat exchanger (1) to the water stored in the water storage tank of metal. Another example of the application of the heat exchanger (1) of this invention is its use in a solar panel. In this application, the bottom surface (18) of the bar (12) of the heat exchanger (1) is in thermal contact with the collector of a solar panel to transfer solar energy harvested by the collector of the solar panel to water flowing through the or each of the tubes (11) of the heat exchanger (1) in a thermosiphon process, heating up water in the or each of the tubes (11) which then rises through a convection process into a water storage tank.

Although the examples above illustrates the transfer of heat from the heat transfer fluid flowing through the heat exchanger (1) to a curved surface, the heat exchanger (1) of this invention can similarly be used to transfer heat from a flat or curved surface to a heat transfer fluid flowing through the heat exchanger (1).

Figs. 2 and 2b show another embodiment of the heat exchanger (2) of this invention. In this embodiment, the heat exchanger (2) comprises an integral piece of metal having a pair of wings (25) and a bar (22) having a top and bottom surfaces (27 and 28), with the pair of wings (25) integrally connected longitudinally to the top surface of a bar (22) and with the pair of wings (25) joined to each other at the end where the wings (25) meets the bar (22) and rising from the top surface (27) of the bar (22), forming a substantially U-shaped channel (23) between the pair of wings (25).

Preferably, the wings (25) are symmetrically located along the longitudinal axis of the bar (12) for balanced heat transfer from the wings (25) to the bar (22). For ease of manufacture and for effective heat transfer, the wings (25) and the bar (22) of the heat exchanger (2) are substantially of the same length. Preferably each of the wings (25) has a hook (26) outwardly bending away from the substantially U-shaped channel (23) at the free end. The hooks (26) facilitate the pressing of the pair of wings

(25) towards one another to circumferentially enclose a tubular electric heating element in the chamber (24) formed by pressing of the wings (25) towards one another.

Fig. 2a shows a heat exchanger (2) of this invention where the bar (22) tapers off gradually at both the longitudinal edges (29) to maximize contact surface with the flat or curved surface and for esthetic reason.

Although Figs. 2 and 2a show only one pair of wings (25) integrally connected to the bar (22), the heat exchanger (2) could have several pair of wings (25) integrally connected to the bar (22). Figs. 2c and 2d show a tubular electric heating element having a pair of terminals connectable to a source of power supply circumferentially enclosed in a chamber (24) of the heat exchanger (2) wherein the chamber (24) is formed by pressing the pair of wings (25) in an inward direction towards the substantially U- shaped channel (23) when the tubular electric heating element (10) is placed in the substantially U-shaped channel (23) and with the internal surfaces of the wings (25) in good thermal contacts with the surface of the tubular electric heating element (10). In Figs. 2c and 2d, a gap is shown between the wings (25) and the tubular electric heating element (10) for illustration purpose only. In practice, there should be direct contacts between the internal surfaces of the wings (25) and the surface of the tubular electric heating element (10) to ensure good thermal contacts..

Fig. 7 shows an application of the heat exchanger illustrated in Figs. 2c and 2d. Referring to Fig. 7, a heat exchanger (7) has two tubular electric heating elements (73) circumferentially enclosed in the respectively chambers (71) of the heat exchanger (7) wherein each chamber (71) is formed by pressing the pair of wings in an inward direction towards the substantially U-shaped channel when the tubular electric heating element is placed in the substantially U-shaped channel and with the internal surfaces of the wings in good thermal contacts with the surface of each of the tubular electric heating element (71). In use, the tubular electric heating elements (71) are connected to an electricity supply via wires (75, 76). Various holes (77) are provided on the heat exchanger (7) for the heat exchanger (7) to be mounted on another apparatus with the aids of studs (not shown).

Fig. 8 shows the use of the heat exchanger with tubular electric heating elements circumferentially enclosed in the chambers (7) in heating up water contained in a water storage tank. The water storage tank has a cylindrical body (81) between

top and bottom covers (82 and 83) with a spaced apart water inlet and outlet pipes (84 and 85) at the top cover (82). The heat exchanger with tubular electric heating elements circumferentially enclosed in the chambers (7) is fixedly mounted on the external surface of the water storage tank of the water heating apparatus (8) in such a way so as to ensure good thermal contact between the external surface of the water storage tank and the bottom surface (78) of the bar (72) of the heat exchanger (7). The bar (72) greatly increases the contact surface between the heat exchanger (7) and the curved surface of the water storage tank, thereby increasing the contact surfaces for heat transfer. Aluminium or its alloys is again the preferred material for the manufacture of heat exchanger (7) of this embodiment.

Referring to Figs. 2c and 2d again, in another application, a tube substitutes the tubular electric heating element (10) described earlier. This embodiment finds useful application where the heat transfer fluid is corrosive to aluminium. In this case, the tube (10) is preferably made of stainless steel or titanium. Referring to Fig. 6 again, the heat exchanger (2) with a tube (not shown) circumferentially enclosed in the chamber (24) can be used to transfer heat from a heat transfer fluid flowing in the tube to a storage tank of a water heating apparatus (6). The water heating apparatus (6) comprises the heat exchanger (2) with a tube circumferentially enclosed in the chamber (24) and a water storage tank of metal. The water storage tank has a cylindrical body (61) between top and bottom covers (62 and 63) with a spaced apart water inlet and outlet pipes (64 and 65) at the top cover (62). The heat exchanger (2) with a tube circumferentially enclosed in the chamber (24) is coiled firmly and tightly around the external surface of the cylindrical body (61) of the water storage tank in a helical or spiral manner such that the bottom surface (28) of the bar (22) of the heat exchanger (2) is in good thermal contact with the external surface of the cylindrical body (61) of the water storage tank to effect transfer of heat from heat transfer fluid flowing through the tube circumferentially enclosed in the chamber (24) in the heat exchanger (2) to the water stored in the water storage tank of metal. Although the examples above illustrate the transfer of heat from the heat transfer fluid flowing through the heat exchanger (2) to a curved surface, the heat exchanger (2) of this invention can be used to transfer heat from a flat or curved surface to a heat transfer fluid flowing through the heat exchanger (2).

Fig. 3 illustrates a heat exchanger (3) for use in the transfer of heat to or from a flat or curved surface with a combination of tube and wings as described earlier. The heat exchanger (3) comprises an integral piece of metal with a combination of two tubes (31, 31a) and a pair of wings (35), with each tube (31 or 31a) and the pair of wings (35) rising from the top surface (37) of a bar (32), forming a substantially U- shaped channel (33) between each pair of wings (35).

Fig. 4 illustrates a heat exchanger (4) for use in the transfer of heat to or from a flat or curved surface wherein the heat exchanger (4) comprises an integral piece of metal with a combination of two tubes (41, 41a) and two pairs of wings (45, 45a), with each of the tubes (41 or 41a) and each pair of wings (45 or 45 a) rising from the top surface (47) of a bar (42), forming respective substantially U-shaped channels (43 or 43 a) between each pair of wings (45 or 45 a).

The descriptions above illustrate that the heat exchanger of this invention can have numerous possible combinations of tubes and wings connected to the bars to transfer heat to or from a flat or curved surface. Figs. 1, 2, 3 and 4 are merely some of the possible combinations.

The foregoing description is considered as illustration of the principles of the invention. Numerous modifications and changes will readily occur to those skilled in the art and all such modifications to the exact construction and operation are intended to be included within the scope of the following claims.