WO2018006117A1

WO2018006117A1 - Heat exchanger improvements

Info

Publication number: WO2018006117A1
Application number: PCT/AU2017/000145
Authority: WO
Inventors: Wasam Saman; Soheila Riahi; Frank Bruno
Original assignee: University of South Australia
Current assignee: Adelaide University
Priority date: 2016-07-05
Filing date: 2017-07-05
Publication date: 2018-01-11
Anticipated expiration: 2019-01-05

Abstract

The present disclosure relates to a heat exchanger system, and to a method of operation of the same. In one aspect, there is provided a heat exchanger system comprising a recuperator type heat exchanger exchanging heat between a first, flowing fluid, and a second fluid, and a means for reversing the flow direction of the flowing fluid repeatedly. In one form, the second fluid is flowing, and the heat exchanger system further comprises a means for reversing the flow direction of the second fluid frequently. An enhancement of heat transfer effectiveness has been found to be up to 30% due to flow reversal, depending on different factors, including the configuration of the heat exchanger, the thermo-physical properties of the fluids involved in the heat exchanger, and the temperature difference between hot and cold media, ΔT=Th-Tc.

Description

HEAT EXCHANGER IMPROVEMENTS

PRIORITY DOCUMENTS

[0001 ] The present application claims priority from Australian Provisional Patent Application No. 2016902640 titled "HEAT EXCHANGER IMPROVEMENTS" and filed on 5 July 2016, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to heat exchangers. In a particular form the present invention relates to a heat exchanger system, and to a method of operation of the same.

BACKGROUND

[0003 ] A heat exchanger is a device for exchanging heat between one medium and one or more others.

[0004] For a fluid to fluid heat exchanger, there is a primary stream that either absorbs or releases energy, and a secondaiy fluid (flowing or stationary) that conversely rejects or absorbs the energy from the primary stream.

[0005] For a fluid to either of a solid or a phase change material heat exchanger, there is a flowing fluid that either absorbs or releases energy, and another fluid, solid, or phase change material that conversely releases or absorbs the energy to change the temperature or the phase.

[0006] The amount of energy that is transferred by the heat exchanger is recognised as its

'effectiveness'. If a heat exchanger were to be able to transfer the maximum possible of the heat energy from one medium to another, it would be rated at 100% effectiveness. While achieving 100% effectiveness is not practical, heat exchangers are generally designed to maximise this effectiveness.

[0007] It is against this background and the problems and difficulties associated therewith that the present invention has been developed.

[0008] Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. SUMMARY

[0009 ] According to a first aspect of the present disclosure, there is provided a heat exchanger system comprising a heat exchanger exchanging heat between a flowing fluid and a medium, and a means for reversing a flow direction of the fluid frequently.

[0010] Ά fluid' may be any one of a liquid, a gas or solid particles, which might be in nano-scale or larger scales.

[ 001 1 ] In one form, the flow reversal means reversing the flow periodically.

10012] In one form, the flow reversal means reversing the flow non-periodically. That is to say, in one form, the flow is reversed in response to an impetus other than time. For example, a temperature of the fluid and/or the medium may be used as the impetus for flow reversal.

[0013] In one form, heat is transferred from the flowing fluid to the medium.

[0014] Ά medium' may be any one of a liquid, a gas, or a solid, including phase change materials which change state from solid to liquid or conversely liquid to solid during the heat exchange process.

[00151 In one form, in an alternative, heat is transferred from the medium to the flowing fluid.

[0016] In one form, the medium comprises a second fluid.

[0017] In one form, the heat exchanger is a recuperator type, in which the two fluids are separated by a dividing wall.

[ 0018] In one form, in an alternative, the medium comprises a solid or solid particles.

[0019] According to a further aspect, there is provided a heat exchanger system comprising a recuperator type heat exchanger exchanging heat between a first, flowing fluid and a second fluid, and a means for reversing the flow direction of the flowing fluid frequently.

[0020] In one form, the second fluid is also flowing.

[00211 In one form, the second and third fluids are flowing.

[0022] In one form, the heat exchanger system comprises a means for reversing the flow direction of the second fluid frequently. [ 0023] In one form, where the exemplary means for reversing the flow direction of the fluid may comprise one or more of a reversible moti ve means, and a control means for controlling the frequent reversal of the motive means.

[0024] In one form, where the flowing fluid is a gas, the reversible motive means may comprise a fan or a compressor.

[0025] In one fonn, where the flowing fluid is a liquid, the reversible motive means comprises a pump.

[0026] In one form, the control means is a manual one, controlled by an operator.

[0027] In one form, the control means is automated.

[0028] In one fonn, the control means comprises a control system.

[0029] In one form, the control means comprises one or more flow control valves, and/or one or more fluid manifolds.

[0030] In one form, the control system may include a variety of components. Exemplary components may include those that monitor electric signals, switch electric signals, perform sensing functions, and govern activation and deactivation of components such as flow control valves, pumps, and fans.

[003 1 ] Further, the control system may comprise a processor, a memory, storage, and a user interface. The control system may be controlled by hardware or software. The control system may provide users with precise control, diagnostic information, and performance information for governing the heat exchanger system.

[0032] In one fonn, the heat exchanger is a shell and tube heat exchanger. [0033] In one form, the heat exchanger is a parallel flow heat exchanger. [ 0034] In one form, the heat exchanger is a counter flow heat exchanger. [0035] In one form, the heat exchanger is a cross flow heat exchanger. [0036] In one form, the heat exchanger is a plate heat exchanger.

[0037] According to a further aspect, there is provided a method of operation of a heat exchanger system comprising a heat exchanger exchanging heat between a flowing fluid and a medium, and a means for reversing the flow direction of the fluid repeatedly, the method comprising the steps of permitting or effecting a flow of the fluid in a first direction through the heat exchanger, reversing the direction of flow after a first time interval, reversing the direction of flow again after a second time interval, and so on.

[0038] According to a further aspect, there is provided a method of operation of a heat exchanger system comprising a heat exchanger exchanging heat between two flowing fluids and a medium, and a means for reversing the flow direction of both fluids repeatedly, the method comprising the steps of pennitting or effecting a flow of the fluids in a first direction through the heat exchanger, reversing the direction of flows after a first time interval, reversing the direction of flows again after a second time interval, and so on.

[0039] According to a further aspect, there is provided a method of operation of a heat exchanger system comprising a plate type heat exchanger exchanging heat between two flowing fluids and either a further fluid, solid or a phase change material, and a means for reversing the flow direction of at least one of the flowing fluids periodically, the method comprising the steps of permitting or effecting the flow of one or both flowing fluids in a respective first direction through the heat exchanger, reversing the direction after a first time interval, reversing direction of the flow after a second time interval, and so on.

[ 0040] In one form, the flow reversal is effected periodically.

[0041 ] In one form, the flow reversal is effected non-periodically.

[0042] In one form, the flow is reversed in response to an impetus other than time.

[0043] An enhancement of heat transfer effectiveness has been found to be up to 30% due to flow- reversal depending on different factors, including the configuration of the heat exchanger, the thermo- physical properties of the fluids involved in the heat exchanger, and the temperature difference between hot and cold media, AT=T_h-T_c.

[0044] In one form, the repetition of reversal is discontinued if ΔΤ drops below a certain degree.

[0045 ] A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications, and equivalents. For the purpose of example, numerous specific detai ls are set forth in the following description in order to provide a thorough understanding of the present invention. [0046] The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

BRIEF DESCRIPTION OF DRAWINGS

[0047] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:

[0048] Figures 1 and 2 are schematic illustrations of a heat exchanger system according to a first embodiment;

[0049] Figures 3 and 4 are schematic illustrations of a heat exchanger system according to a second embodiment; and

[0050] Figure 5 is a schematic illustration of a heat exchanger system according to a third embodiment.

[00511 In the following description, like reference characters designate like or corresponding parts throughout the figures.

DESCRIPTION OF EMBODIMENTS

[0052] Referring now to Figures 1 and 2, where there is illustrated a heat exchanger system 1 comprising a recuperator type heat exchanger 10 exchanging heat between a first, flowing fluid Fl and a second fluid F2. One example of such an arrangement is a hot water tank.

[0053 ] Heat exchanger system 1 further comprises a means for reversing the flow direction of the flowing fluid F l repeatedly. The heat exchanger system 1 comprises a fluid circuit C I for the first fluid F l , comprising a tank (or reservoir) T l for the first fluid Fl , connected to a remainder of the fluid circuit C I by inlet and outlet lines 1 and O, respectively.

[0054] The inlet line I comprises a motive means in the form of a reversible pump P and extends to a first 3-way valve 31 comprising three ports A, B and C, and more particularly, to the port A of the 3-way valve 31.

[0055] The outlet line O extends to a second 3-way valve 30 comprising three ports X, Y and Z, and more particularly, to the port X of the 3-way valve 30. [0056] The operation of the 3-way valves 31 and 30 is controlled by a control system, to control the actuation of the valves.

[0057] With reference to Figure 1 , it can be seen how in use, the control system will initially set the 3- way valves 31 and 30 so that the fluid F 1 flows into the heat exchanger 10 via port C of 31, from the heat exchanger 10 to port Z of 30, and returns to the tank Tl via the port X of 30 and outlet line O.

[0058] With reference to Figure 2, it can be seen how after either of a predetermined time, or in response to one or more inputs, the control system will reverse the direction of flow of fluid F l . This is effected by changing the settings of the 3-way valves 31 and 30 so that the fluid F l flows into the heat exchanger 10 via port B of 31, from the heat exchanger 10 to port Y of 30, and returns to the tank T 1 via the outlet line O.

[0059] With reference to Figure 1 again, after either of a further predetermined time, or in response to one or more inputs, the control system will again reverse the direction of flow of fluid Fl . This is effected by changing the settings of the 3-way valves 31 and 30 so that fluid F l flows into the heat exchanger 10 via port C of 31, from the heat exchanger 10 to port Z of 30, and returns to the tank T 1 via the outlet line O.

[0060] In use, the control system will monitor the temperature of the hot fluid T_h and the temperature of the cold fluid T_c, and discontinue the flow reversal if temperature difference between hot and cold media, AT=T_h-T_c, drops below a certain degree.

[0061 ] Referring now to Figure 5, where there is illustrated a heat exchanger system 50 comprising a plate heat exchanger 60 exchanging heat between two flowing fluids Fl and F2, and either of a fluid, a solid or a phase change material F3.

[0062] Heat exchanger system 50 further comprises a means for reversing the flow direction of the flowing fluid F l repeatedly. This means is identical to, and works the same as, the flow reversal means for heat exchanger system 1 described above, and so those parts which are identical (or near- identical) to corresponding parts shown in system 1 will be denoted by the same reference numerals, and will not be described again in detail here.

[0063] In heat exchange systems of the above described types, ΔΤ diminishes over time, and flow- reversal loses its effectiveness gradually, meaning in some cases, flow reversal should be used only for a definite period of time, while ΔΤ is high enough. In practice, the control system could be used to ensure this, and to discontinue flow reversal if the ΔΤ drops below a certain degree. [0064] Referring now to Figures 3 and 4, where there is illustrated a heat exchanger system 100 comprising a recuperator type heat exchanger 20 exchanging heat between a first, flowing fluid F l and a second, flowing fluid F2, and a means for reversing the flow direction of the flowing fluids periodically.

[0065] The heat exchanger system 100 comprises a first fluid circuit C I for the first fluid F l , and a second fluid circuit C2 for the second fluid F2.

[0066] The second fluid circuit C2 is identical to the first fluid circuit C I so it will not be described again in detail.

[0067] In use, the control system will periodically reverse the flow of both fluids Fl and F2, in the manner described above.

[0068] At certain times the 3-way valves 31 and 30 may be so set that the heat exchanger 20 is operating as a parallel flow type heat exchanger. At other times the 3-way valves 31 and 30 may be so set that the heat exchanger 20 is operating as a counter flow type heat exchanger.

[0069] With reference to Figure 3, it can be seen how in use, the control system will initially set the 3- way valves 31 and 30 of fluid circuit C I so that fluid F l flows into the heat exchanger 20 via port C of 31, from the heat exchanger 10 to port Z of 30, and returns to the tank T 1 via the outlet line O.

[0070] With reference to fluid F2 and circuit C2, the control system will initially set the 3-way valves 31 and 30 so that the fluid F2 flows into the heat exchanger 20 via port A and B of 31, and to the heat exchanger 20 via port Y of 30, and returns to the tank T2 via the outlet line O.

[00711 With reference to Figure 4, it can be seen how after either of a predetermined time, or in response to one or more inputs, the control system will reverse the direction of flow of both fluid Fl and fluid F2.

[0072] In heat exchangers of the above described type (i.e. of Figures 3 and 4), with two fluids in parallel or counter flow configuration, e.g. a radiator in which hot oil is cooled by a water flow, application of flow reversal resulted in more than 30% enhancement of heat transfer. Flow reversal according to the present invention is more effective in a counter flow heat exchanger configuration.

[0073] Moreover, in steady state systems such as this, where ΔΤ remains substantially constant during the process, flow reversal remains effective throughout the process.

[0074] In a Latent Heat Thermal Storage system which involves a phase change material and a heat transfer fluid, flow reversal was proved to enhance the heat transfer by at least about 6%. [0075] A further possible, but non-illustrated embodiment combines the system of Figures 3 and 4 with the plate heat exchanger 60 of Figure 5.

[0076] The systems of Figures 1 through 4 include gate valves VI through V4, but these are not material to the operation of the inventive concept, and so they are omitted in Figure 5.

[0077] Possible applications for the present invention include a wide range of applications where recuperative heat exchangers are used. These include but are not limited to, space heating, refrigeration, air conditioning, car radiators, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and water tr eatment plants.

[0078] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0079] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0080] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims

1. A heat exchanger system comprising a heat exchanger exchanging heat between a flowing fluid and a medium, and a means for reversing the flow direction of the fluid frequently.

2. The heat exchanger system of claim 1, wherein the medium comprises a second fluid.

3. The heat exchanger system of claim 2, wherein the heat exchanger is a recuperator type, in which the two fluids are separated by a dividing wall.

4. A heat exchanger system comprising a recuperator type heat exchanger exchanging heat between a first, flowing fluid, and a second fluid, and a means for reversing the flow direction of the flowing fluid repeatedly.

5. The heat exchanger system of claim 4, wherein the second fluid is flowing.

6. The heat exchanger system of claim 5, wherein the heat exchanger system comprises a means for reversing the flow direction of the second fluid frequently.

7. The heat exchanger system as in any one of the preceding claims, wherein the or each means for reversing the flow direction of the fluid comprises a reversible motive means, and a control means for controlling the frequent reversal of the motive means.

8. The heat exchanger system as in any one of the preceding claims, wherein the or each means for reversing the flow direction of the fluid comprises one or more flow control valves, and/or one or more fluid manifolds.

9. The heat exchanger as in either of claims 7 or 8, wherein the or each reversible motive means comprises at least one of a fan or a compressor or a pump.

10. The heat exchanger as in any one of claims 7 through 9, wherein the control means is a manual one, controlled by an operator.

1 1. The heat exchanger as in any one of claims 7 through 9, wherein the control means is automated.

12. The heat exchanger of claim 1 1, wherein the control means comprises a control system.

13. The heat exchanger system as in any one of the preceding claims, wherein the heat exchanger is a shell and tube heat exchanger.

14. The heat exchanger system as in any one of the preceding claims, wherein the heat exchanger is a parallel flow heat exchanger.

15. The heat exchanger system as in any one of claims 1 through 12, wherein the heat exchanger is a counter flow heat exchanger.

16. The heat exchanger system as in any one of claims 1 through 12, wherein the heat exchanger is a cross flow heat exchanger.

17. The heat exchanger as in any one of claims 1 through 12, wherein the heat exchanger is a plate type heat exchanger.

18. A method of operation of a heat exchanger system comprising a heat exchanger exchanging heat between a flowing fluid and a medium, and a means for reversing the flow direction of the fluid repeatedly, the method comprising the steps of permitting or effecting a flow of the fluid in a first direction through the heat exchanger, reversing the direction of flow after a first time interval, reversing the direction of flow again after a second time interval, and so on.

19. The method of claim 18, wherein the flow reversal is effected periodically.

20. The method of claim 18, wherein the flow reversal is effected non-periodically.

21. The method of claim 20, wherein the flow is reversed in response to an impetus other than time.

22. The method as in any one of claims 19 through 21, wherein the repetition of reversal is discontinued if ΔΤ drops below a certain degree.

23. A method of operation of a heat exchanger system comprising a recuperator type heat exchanger exchanging heat between a first flowing fluid and a second flowing fluid, and a means for reversing the flow direction of both flowing fluids repeatedly, the method comprising the steps of permitting or effecting a flow of both fluids in a respective first direction through the heat exchanger, reversing the direction of both flows after a first time interval, reversing the direction of both flows again after a second time interval, and so on.

24. The method of claim 23, wherein each flow reversal is effected periodically.

25. The method of claim 23, wherein each flow reversal is effected non-periodically.

26. The method of claim 23, wherein each flow is reversed in response to an impetus other than time.

27. A method of operation of a heat exchanger system comprising a plate type heat exchanger exchanging heat between two flowing fluids and either a further fluid, or a solid or a phase change material, and a means for reversing the flow direction of at least one of the flowing fluids periodically, the method comprising the steps of permitting or effecting the flow of the or each flowing fluid in a respective first direction through the heat exchanger, reversing the direction after a first time interval, reversing direction of the flow after a second time interval, and so on.