GB2490704A

GB2490704A - Heat exchanger having two chambers in thermal communication through an array of heat pipes

Info

Publication number: GB2490704A
Application number: GB1107814.4A
Authority: GB
Inventors: Dumitru Fetcu
Original assignee: Econotherm UK Ltd
Current assignee: Econotherm UK Ltd
Priority date: 2011-05-11
Filing date: 2011-05-11
Publication date: 2012-11-14
Also published as: WO2012153103A9; EP2707670A2; WO2012153103A3; WO2012153103A2; GB201107814D0

Abstract

The heat exchanger comprises a first chamber having a respective inlet 106 and outlet 107; a second chamber having a respective inlet 108 and outlet 109; and an array of heat pipes 105 extending from within the first chamber to within the second chamber. A first 112 and second 113 partition separate the first and second chamber and may define a third chamber 115 in which apparatus can be located to detect leakage of fluid from the first or second chamber. The heat pipes extend through the first and second partitions and transfer heat energy there between. The heat pipes are coupled with each partition, preferably via a sealing assembly (114, figure 7). A perforated plate 120 may be disposed near the inlet of the first chamber to reduce a flow rate of fluid passing through the first chamber, thereby improving heat transfer between fluid and the heat pipes. The second chamber may comprise two separate compartments (103a and 103b, figure 3) fluidly communicated by conduits.

Description

Heat Exchanger The present invention relates to a heat exchanger and particularly, but not exclusively to a heat exchanger comprising heat pipes.

A heat pipe is a hermetically sealed, evacuated tube typically comprising a mesh or sintered powder wick and a working fluid in both the liquid and vapour phase. When one end of the tube is heated the liquid turns to vapour upon absorbing the latent heat of vaporization. The hot vapour subsequently passes to the cooler end of the tube where it condenses and gives out the latent heat to the tube. The condensed liquid then flows back to the hot end of the tube and the vaporization-condensation cycle repeats. Since the latent heat of vaporization is usually very large, considerable quantities of heat can be transported along the tube and a substantially uniform temperature distribution can be achieved along the heat pipe.

Heat exchangers 10 typically comprise two chambers 11, 12, as illustrated in figure 1 of the drawings, which are separately arranged to receive a fluid between which heat transfer is desirable. The chambers 11, 12 are separated by a separation plate 13, and a plurality of heat pipes 14 are arranged to extend between the chambers 11, 12, through the separation plate 13, to transfer heat between the chambers 11, 12 and thus the fluids. In this respect, by passing a heated fluid through of one chamber 11, via the respective inlet 11 a and outlet 11 b, the heat pipes 14 can transfer the heat absorbed from the heated fluid to the other chamber 12 wherein a cooled fluid may pass, via the respective inlet 12a and outlet (not shown), to subsequently absorb the heat from the heat pipes 14.

It is known to utilise heat exchangers to harvest heat from exhaust gases for example, to generate electricity. During so-called organic Rankine cycles, the heat extracted from an industrial exhaust gas in one chamber of the exchanger is used to heat an oil in the adjacent chamber of the exchanger. The oil undergoes a liquid-vapour phase change at a temperature lower than a water-steam phase change for example, and as such allows heat recovery from lower temperature sources. However, such oils are typically expensive and can decompose if exposed to too high a temperature. Moreover, any leakage of the oil from the cooler chamber into the hotter (exhaust gas) chamber presents a lire hazard and so it is necessary to ensure that the oil cannot pass between chambers ol the heat exchanger.

In accordance with the present invention as seen Irom a lirst aspect, there is provided a heat exchanger br exchanging heat between a birst and second bluid, the exchanger comprising a birst heat exchanging chamber, a second heat exchanging chamber and an array ob heat pipes which are arranged to extend brom within the birst heat exchanging chamber to within the second heat exchanging chamber to transler heat between the birst and second chambers; the birst heat exchanging chamber comprising an inlet br receiving a birst bluid into the chamber and an outlet through which the birst bluid can exit the birst chamber, the birst bluid being arranged to pass over the portion ob the heat pipes which extend within the birst chamber; the second heat exchanging chamber comprising an inlet br receiving the second bluid into the chamber and an outlet through which the second bluid can exit the second chamber, the second bluid being arranged to pass over the portion ob the heat pipes which extend within the second chamber; the heat exchanger burther comprising a birst and second partition which are arranged to separate the birst bluid in the birst chamber brom the second bluid in the second chamber, the heat pipes being arranged to extend through the birst and second partitions and which are separately arranged to sealingly couple with each partition.

Advantageously, the birst and second partitions provide a level ob redundancy so that in the event that the seal between the heat pipes in one chamber and the respective partition or separation plate becomes compromised, the burther partition will prevent any communication ob bluid between chambers.

The birst and second partitions are preberably arranged in spaced relation to debine a third chamber therebetween. Preberably, the birst and second partitions comprise a plurality ob apertures which are arranged to separately receive the heat pipes. The birst and second partitions preberably comprise birst and second plates which are orientated in a substantially parallel conbiguration.

The third chamber preferably comprises monitoring means for monitoring any ingress of first and/or second fluid from the respective first or second chamber into the third chamber.

Preferably, the first and second partitions comprise a plurality of apertures, the apertures disposed in the first partition being separately aligned with a corresponding aperture disposed within the second partition. Aligned pairs of apertures are preferably separately arranged to receive a heat pipe.

The heat pipes are preferably separately arranged to sealing couple with each partition using a sealing assembly. The sealing assembly preferably comprises a sleeve which is arranged to extend over the portion of the heat pipes which extends within the third chamber.

Each sleeve of the assembly preferably comprises an externally threaded portion which is arranged to detachably couple within an internally threaded portion disposed within an aperture of the first partition.

The sealing assembly preferably further comprises an externally threaded collar which is arranged to extend over the sleeve and detachably coupled with an internally threaded portion disposed within the corresponding aligned aperture in the second partition.

Preferably, the sleeve is rigidly coupled to the respective heat pipe.

In heat recovery systems whereby heat is recovered from exhaust gases which pass through ducts under high pressure and with a high mass flow rate, it is found that upon entering the respective chamber of a heat exchanger, only a selected number of heat pipes, namely those disposed directly adjacent the inlet to the chamber, participate in the extraction of heat from the gas. Since the gas is directed into the chamber with a high velocity, it becomes substantially undeflected in travelling to the outlet and as such, does not spread out to reach whole array of heat pipes. This has the result of reducing the efficiency of the heat exchanger and thus less heat recovery from the gas.

In accordance with the present invention as seen from a second aspect, there is provided a heat exchanger for exchanging heat between a first fluid flow and a second fluid flow, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber to transfer heat between the first and second chambers; the first heat exchanging chamber comprising an inlet for receiving the first fluid into the chamber and an outlet through which the first fluid can exit the first chamber, the exchanger further comprising diffusing means for reducing a rate of flow of the first fluid across the portion of the heat pipes within the first chamber and for deflecting the first fluid flow across the array of heat pipes within the first chamber, in passing between the inlet and the outlet of the first chamber.

The diffusing means thus provides for an improved extraction of heat from a gas for example, which would otherwise pass through a chamber of the heat exchanger with a high velocity and thus interact very little with the heat pipes.

The diffusing means is preferably disposed between the inlet to the first chamber and the array of heat pipes within the first chamber.

Preferably, the diffusing means comprises a perforated plate.

In heat recovery systems whereby the heat is recovered from industrial exhaust fluids, for example, which pass along an exhaust duct with a high mass flow rate under high pressure, it is necessary to employ a large number of heat pipes to provide the required levels of heat extraction. However, a problem with using a large number of heat pipes is that the heat exchanger, and more particularly, the separation plate becomes very large and as such it is difficult to suitably install and seal the heat pipes within the separation plate to prevent the fluids within the chambers from mixing. Furthermore, the large numbers of heat pipes reduces their accessibility for maintenance and repair, for

example.

In an attempt to overcome this problem, heat exchanging systems have been proposed in which the exhaust duct is split into smaller exhaust ducts which separately feed exhaust fluid into a chamber associated with a separate heat exchanger. In this respect, the systems comprise a plurality of heat exchangers arranged in a parallel configuration.

A problem with this set-up however, is that it is difficult to ensure a uniform separation of the exhaust fluid between the heat exchangers so that the mass flow rate of fluid is uniform within each heat exchanger, and as such it is difficult to control the heat exchange from the exhaust fluid.

In accordance with the present invention as seen from a third aspect, there is provided a heat exchanger for exchanging heat between a first and second fluid, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber to transfer heat between the first and second chambers; the first heat exchanging chamber being arranged to pass a first fluid over the portion of the heat pipes which extend within the first chamber; the second heat exchanging chamber being arranged to pass a second fluid over the portion of the heat pipes which extend within the second chamber; wherein, the array of heat pipes comprises a first sub-array and a second sub-array which are separately arranged to extend through a first and second partition respectively, the first and second partitions being arranged to separate the first and second chambers to minimise any communication of fluid between the first and second chamber.

The provision of two partitions, namely separation plates, facilitates an improved installation and replacement of heat pipes within the exchanger, since each partition is required to include less heat pipes than that which would be necessary if only a single partition was used. In this respect, the first and second sub arrays and thus the first and second partitions are preferably centered at separated positions across the heat exchanger.

Preferably, the first and second partition are arranged to extend in substantially the same plane.

The exchanger preferably further comprises a vane disposed within the first chamber for splitting the flow of fluid across each sub-array within the first chamber. The vane is preferably arranged to extend between an upper and lower wall of the first chamber, substantially perpendicular to the first and second partitions.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional plane view of a known heat pipe heat exchanger; Figure 2 is a side view of a heat exchanger according to an embodiment of the present invention comprising a first and second partition, a first and second sub-array of heat pipes and diffusing means; Figure 3 is a plan view of the heat exchanger illustrated in figure 2; Figure 4 is a longitudinal sectional plane view of the heat exchanger illustrated in figure 2, taken along line A-A, as illustrated in figure 3; Figure 5 is a transverse sectional plane view of the heat exchanger illustrated in figure 2, taken across line B-B; Figure 6 is a transverse sectional plane view of the heat exchanger illustrated in figure 2, taken across line C-C; Figure 7 is a magnified view of the first and second partitions illustrated in figure 4, illustrating the collar; and Figure 8 is a view of the perforated plate illustrated in figure 2, taken from the exhaust gas inlet to the first chamber.

Referring to the drawings and initially figures 2 to 6, there is illustrated a heat exchanger according to an embodiment of the present invention for exchanging heat between a first fluid such as heated exhaust gas from an industrial process, and a second fluid such as an oil. The heat exchanger 100 may form part of a so-called organic Rankine cycle whereby the heat transferred to the oil may be used to drive turbines (not shown) to generate electricity.

The heat exchanger 100 comprises a housing 101 which defines a first and second heat exchanging chamber 102, 103 disposed one above the other and arranged such that a longitudinal axis of each chamber are substantially parallel. The second chamber 103 is disposed upon the first chamber 102 and comprises a first and second compartment 103a, 103b, which are arranged in fluid communication by a flow conduit 104a and a return conduit 104b. The exchanger 100 further comprises a plurality of elongate heat pipes 105 orientated substantially parallel to each other and to the longitudinal axis of the chambers 103a, 103b, and are arranged to transfer heat between the first and second chambers 103a, 103b.

The heat pipes 105 are configured in a first and second, substantially hexagonal array 105a, 105b which are centered at separated positions across the heat exchanger 100, and which extend from within the first chamber 102 to a respective compartment 103a, 103b of the second chamber 103. The first chamber 102 comprises an inlet 106 for receiving hot exhaust gas from an industrial process into the first chamber 102, and an outlet 107 through which the exhaust gas can exit the first chamber 102. The second chamber 103 comprises an inlet 108 disposed on the first compartment 103a for receiving cool oil into the second chamber 103 and an outlet 109 disposed in the second compartment 103b via which heated oil can exit the second chamber 103 for the subsequent generation of electricity.

The compartments 103a, 103b of the second chamber 103 separately comprise a plurality of screens 110 which extend substantially parallel to the heat pipes 105 and which extend between upper and lower walls of the second chamber 103 to define a flow path for the oil in the respective compartment. In this respect and referring to figure 6 of the drawings, the oil is arranged to pass from the inlet 108 to the second chamber 103, into the first compartment I 03a and along a flow path defined by a screen 109 within the first compartment 103a, to the flow conduit 104a which communicates the oil to a flow path in the second compartment 103b. The flow path in the second compartment 103b is arranged to return the oil to a further flow path in the first compartment I 03a via a return conduit I 04b, so that the oil can exit the second chamber 103 via the outlet 109.

Each compartment 103a, 103b of the second chamber 103 is closed at its upper end via an end wall 111, whereas the lower end of each compartment comprises a first and second partition or separation plate 112, 113 which prevent the oil in the compartments 103a, 103b from passing into the first chamber 102 and which similarly prevent the gas in the first chamber 102 from passing into the compartments 103a, 103b of the second chamber 103. The separation plates 112, 113 corresponding to each compartment 103a, 103b extend in a spaced, substantially parallel orientation and are sealed at their periphery to the housing 101 to prevent any communication of fluid between the chambers 102, 103. The heat pipes 105 separately extend through aligned pairs of apertures (not shown) disposed within the separation plates 112, 113 and each of the plurality of heat pipes 105 are sealed to both plates 112, 113 using a sealing assembly 114, as illustrated in figure 7 of the drawings. In this respect, the separation plates 112, 113 corresponding to each compartment 103a, 103b define a third chamber 115 therebetween which are arranged to house monitoring means (not shown) for monitoring for the presence of any exhaust gas or oil which leaks from the respective chamber 102, 103 into the third chamber 115.

Each sealing assembly 114 comprises a substantially cylindrical sleeve 116 which is used to seal the respective heat pipe 105 to the separation plates 112, 113, and is arranged to extend over a portion of the heat pipes 105. Each sleeve 116 is welded or otherwise bonded to a respective heat pipe 105 at a position intermediate opposite ends thereof, such that the heat pipes 105 suitably extend into the respective chambers 102, 103. The sleeves 116 are welded around the periphery thereof at each longitudinal end 116a, 116b thereof, to the heat pipes 105, to seal the sleeve 116 to the heat pipe 105 so that fluid is prevented from passing between the heat pipe 105 and the sleeve 116.

Each sleeve 116 comprises a circumferentially extending shoulder portion 117 disposed adjacent one longitudinal end 116a thereof, having an externally threaded portion (not shown) disposed thereon, which is arranged to detachably couple with an internally threaded portion (not shown) disposed within an aperture (not shown) of the first separation plate 112 The shoulder 117 is arranged to compress a sealing ring 118a or gasket within the aperture (not shown) as the sleeve 116 and thus the respective heat pipe 105 is screwed therein, to seal the sleeve 116 to the first separation plate 112. In this respect, the heat pipes 105 become supported within the heat exchanger by the first separation plate 112.

When the sleeve 116 and thus the respective heat pipe 105 is suitably coupled within an aperture (not shown) of the first separation plate 112, the other longitudinal end 116b of the sleeve 116 is arranged to extend within the aligned aperture (not shown) in the second separation plate 113, into the into a compartment 103a, 103b of second chamber 103.

Each sealing assembly 114 further comprises a substantially cylindrical collar 119 which is arranged to extend over the other longitudinal end 116b, from within the respective compartment 103a, 103b of the second chamber 103. The collar 119 comprises an externally threaded portion (not shown) which is arranged to detachably couple with an internally threaded portion (not shown) disposed within the aperture (not shown) within the second separation plate 113, through which the sleeve 116 extends. The collar 119 is arranged to screw within the aperture (not shown) in the second separation plate 113 and compress a sealing ring 11 8b or gasket within the aperture (not shown) to seal the sleeve 116 to within the aperture (not shown).

Referring to figure 8 of the drawings, the heat exchanger 100 further comprises diffusing means, such as a perforated plate 120 or disc, disposed between the exhaust gas inlet 106 to the first chamber 102 and the array of heat pipes 105. The plate 120 illustrated in figure 8 of the drawings is substantially rectangular and is shaped to sealing couple with the cross-section of the inlet housing, so that the gas is prevented from passing around the plate 120 between the plate 120 and the housing 101.

The plate 120 comprises a plurality of perforations or apertures 121 disposed therein which are arranged to disperse a substantially directional gas flow around the first chamber 102 so that the gas can interact and thus exchange heat with the heat pipes 105 of the first and second sub array 105a, 105b. To further assist this dispersal, the first chamber 102 comprises a substantially planar vane 122 (as illustrated in figure 5 of the drawings) disposed between the sub-arrays 105a, 105b, which is orientated substantially parallel to the heat pipes 105. The vane 122 comprises a leading edge 123 disposed adjacent the inlet 106, which is arranged to deflect the gas from the inlet 106 either side of the vane 122 toward each sub-array 105a, 105b of heat pipes 105 to encourage the interaction of the gas with the heat pipes 105.

Accordingly, during use, a high mass flow rate of hot exhaust gas may be passed into the first chamber 102 via the inlet 106. The directional flow of gas into the chamber 102 is interrupted by the perforated plate 120 which serves to slow the gas flow speed and disperse the gas across the portion of the heat pipes 105 which extend within the first chamber 102. The vane 122 further serves to deflect any gas flow which passes directly through the perforated plate 120 from the inlet 106, across the heat pipes 105, to prevent the gas from simply passing directly to the outlet 107 without undergoing any heat exchange.

As the exhaust gas passes through the first chamber 102 it becomes cooled as the heat pipes 105 absorb the heat therefrom and so the gas which leaves the first chamber 102 is substantially cooled. The heat absorbed by the heat pipes 105 is transferred along the heat pipes 105 to the second chamber 103 whereupon it becomes absorbed by the flow of oil therein. The oil which passes over the portion of the heat pipes 105 in the second chamber 103 subsequently becomes heated in passing from the inlet 108 to the outlet 109 thereof as it absorbs the heat from the heat pipes.

The arrangement of two sets of separation plates 112, 113 between the chambers, namely one set between the first compartment 103a and the first chamber 102 and the other between the second compartment 103b and the first chamber 102, ensures the gas in the first chamber 102 and the oil in the second chamber 103 remain separated.

The air filled chambers 115 between the first and second chamber 102, 103 further serves to insulate the first and second chambers 102, 103 from each other to minimise the direct transfer of heat between chambers 102, 103, which would be significant if only a single separation plate was employed and thus provide for a controlled exchange of heat.

The above described heat exchanger 100 includes an embodiment of each of the present inventions, whereas it is to be appreciated that a heat exchanger comprising only one embodiment of the present invention may be necessary to suit a particular heat recovery system. For example, in heat exchangers which comprise a low mass flow rate of exhaust gas, but which require minimal communication of fluids between chambers 102, 103, then only a single array of heat pipes may be required in which case, the heat exchanger may be provided without the perforated plate 120 and vane 122. Similarly, heat exchangers which receive a high mass flow rate of exhaust gas and which have less stringent criteria regarding the communication of fluids between chambers 102, 103, then the above described heat exchanger may be provided with only a single separation

plate, for example.

From the foregoing therefore, it is evident that the heat exchanger of the present invention provides for an improved exchange and thus recovery of heat from fluids.

Claims

Claims 1. A heat exchanger for exchanging heat between a first and second fluid, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber to transfer heat between the first and second chambers; the first heat exchanging chamber comprising an inlet for receiving a first fluid into the chamber and an outlet through which the first fluid can exit the first chamber, the first fluid being arranged to pass over the portion of the heat pipes which extend within the first chamber; the second heat exchanging chamber comprising an inlet for receiving the second fluid into the chamber and an outlet through which the second fluid can exit the second chamber, the second fluid being arranged to pass over the portion of the heat pipes which extend within the second chamber; the heat exchanger further comprising a first and second partition which are arranged to separate the first fluid in the first chamber from the second fluid in the second chamber, the heat pipes being arranged to extend through the first and second partitions and which are separately arranged to couple with each partition.
2. A heat exchanger according to claim 1, wherein the first and second partitions are arranged in spaced relation to define a third chamber therebetween.
3. A heat exchanger according to claim I or 2, wherein the first and second partitions comprise a plurality of apertures which are arranged to separately receive the heat pipes.
4. A heat exchanger according to any preceding claim, wherein the first and second partitions comprise first and second plates which are orientated in a substantially parallel configuration,
5. A heat exchanger according to claim 2, wherein the third chamber comprises monitoring means for monitoring any ingress of first and/or second fluid from the respective first or second chamber into the third chamber.
6. A heat exchanger according to any preceding claim, wherein the first and second partitions comprise a plurality of apertures, the apertures disposed in the first partition being separately aligned with a corresponding aperture disposed within the second partition.
7. A heat exchanger according to claim 6, wherein aligned pairs of apertures are separately arranged to receive a heat pipe.
8. A heat exchanger according to any preceding claim, wherein the heat pipes are separately arranged to sealing couple with each partition using a sealing assembly.
9. A heat exchanger according to claim 8, wherein the sealing assembly comprises a sleeve which is arranged to extend over the portion of the heat pipes which extends between the first and second chamber.
10. A heat exchanger according to claim 8 or 9, wherein each sleeve of the assembly comprises an externally threaded portion which is arranged to detachably couple within an internally threaded portion disposed within an aperture of the first partition.
11. A heat exchanger according to claim 10 as appended to claim 7, wherein the sealing assembly further comprises an externally threaded collar which is arranged to extend over the sleeve and detachably coupled with an internally threaded portion disposed within the corresponding aligned aperture in the second partition.
12. A heat exchanger according to claim 9, wherein the sleeve is rigidly coupled to the respective heat pipe.
13. A heat exchanger for exchanging heat between a first fluid flow and a second fluid flow, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber to transfer heat between the first and second chambers; the first heat exchanging chamber comprising an inlet for receiving the first fluid into the chamber and an outlet through which the first fluid can exit the first chamber, the exchanger further comprising diffusing means for reducing a rate of flow of the first fluid across the portion of the heat pipes within the first chamber and for deflecting the first fluid flow across the array of heat pipes within the first chamber, in passing between the inlet and the outlet of the first chamber.
14. A heat exchanger according to claim 13, wherein the diffusing means is disposed between the inlet to the first chamber and the array of heat pipes within the first chamber.
15. A heat exchanger according to claim 13 or 14, wherein the diffusing means comprises a perforated plate.
16. A heat exchanger for exchanging heat between a first and second fluid, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber to transfer heat between the first and second chambers; the first heat exchanging chamber being arranged to pass a first fluid over the portion of the heat pipes which extend within the first chamber; the second heat exchanging chamber being arranged to pass a second fluid over the portion of the heat pipes which extend within the second chamber; wherein, the array of heat pipes comprises a first sub-array and a second sub-array which are separately arranged to extend through a first and second partition respectively, the first and second partitions being arranged to separate the first and second chambers to minimise any communication of fluid between the first and second chamber.
17. A heat exchanger according to claim 16, wherein the first and second sub-arrays are centered at separated positions across the heat exchanger.
18. A heat exchanger according to claim 17, wherein the first and second partition are arranged to extend in substantially the same plane.
19. A heat exchanger according to any of claims 16 to 18, further comprising a vane disposed within the first chamber for splitting the flow of fluid across each sub-array within the first chamber.
20. A heat exchanger according to claim 19, wherein the vane is arranged to extend between an upper and lower wall of the first chamber, substantially perpendicular to the first and second partitions.