AU644873B2

AU644873B2 - Thermosyphon

Info

Publication number: AU644873B2
Application number: AU77169/91A
Authority: AU
Inventors: Aliakbar Akbarzadeh; Kevin Arthur Gibson; Peter William Johnson
Original assignee: Technisearch Ltd
Current assignee: Technisearch Ltd
Priority date: 1990-05-18
Filing date: 1990-05-18
Publication date: 1993-12-23
Anticipated expiration: 2011-05-17
Also published as: NZ238185A; AU7716991A

Description

644873

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Regulation 3.2

S

4, Name of Applicant: TECHNISEARCH LTD.

4 .4 Address for Service: DAVIES COLLISON, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

S.

Invention Title: THERMOSYPHON Details of Associated Provisional Application(s): No(s): PK 0201/90 Filed 18 May 1990 The following statement is a full description of this invention, including the best method of performing it known to us: -1r -2-

'THERMOSYPHON"

The present invention relates to gravity assisted heat pipes or thermosyphons.

A heat pipe usually comprises an elongate sealed cylinder containing a vaporisable material having liquid and vapour phases at the temperatures of operation of the heat pipe. Heat applied to one end portion of the cylinder, known as the evaporator section, vaporises the liquid. The vapour then flows in a high speed stream to the other end portion of the cylinder, known as the So.* condenser section, which is maintained at a lower temperature than the evaporator section causing the vapour to condense whereby heat is given off.

The heat pipe provides very efficient heat transfer between a higher temperature zone surrounding the evaporator section and a lower temperature 0 15 zone surrounding the condenser section. The temperature difference between the two sections need not be substantial. The vapour condenses in the condenser section and is returned to the evaporator section by means of the capillary action of a wick structure affixed to the inner surface of the cylinder.

The evaporation rate, and consequently the heat transfer rate, is determined by the amount of liquid available for evaporation in the evaporator section. The es' rate of return of the condensate is thus a limiting factor in the operation of the heat pipe and, in some instances, a fluid pump is required to enhance this return rate. A thermosyphon is a simple form of heat pipe where the return of the condensate from the condenser section to the evaporator section is o 25 achieved by gravity. Therefore thermosyphons are also called gravity assisted heat pipes.

Various proposals have been made to convert the thermal energy of the vapour stream into electrical energy by placing a turbine, connected to a generator, in the path of the vapour stream. The higher the kinetic energy of the vapour as it flows through the turbine the greater the electrical power produced. The present invention seeks to provide a thermosyphon turbine 910517,pavMl.technspe,2 system in which the kinetic energy of the vapour is increased so as to obtain a rne.c higher electrical (or) power output.

The present invention seeks also to provide an effective, simple and passive liquid return system from the condenser low pressure environment to the evaporator section which is at a higher pressure.

According to the present invention there is provided a thermosyphon comprising an enclosure containing a vaporisable material, said enclosure comprising an evaporator section at a lower end portion wherein the material is heated and vaporised, an adiabatic section through which the vapour flows, a condenser section at an upper end portion wherein the vapour condenses, collection means to collect the condensate, at least one return pipe to return the condensate from the collection means to the evaporator section, separator 15 means separating the evaporator section from the condenser section to thereby, in use, provide a differential pressure therebetween, the separator means having at least one aperture for flow therethrough of the vapour, and a turbine mounted downstream of the separator means to be driven by the Svapour stream flowing through the aperture.

The separator means supports the pressure difference between the evaporator and condenser sections to enable a high velocity flow out of the nozzles.

The thermosyphon finds particular utility in the production of energy from 25 such diverse low temperature heat sources as solar ponds and geothermal systems and the structure of the enclosure may be rigid or part flexible depending on the particular application.

In most cases having a rigid construction the thermosyphon will be subtsantially vertical in use. However, the alignment of the thermosyphon will depend on the location and use to which it is to be put.

/910517 .tech spe,3 910517.pa01.techn.spe,3 r,~ -4- Alternatively, provided that the portion of the enclosure adjacent the turbine is substantially rigid so as not to interfere with the rotation of the turbine, one or more of the other portions of the enclosure may be flexible. Thus, for example, if the thermosyphon is to be used to produce energy from a non-linear geothermal bore, portions of the enclosure, such as the evaporator and adiabatic sections, may be flexible so as to allow the thermosyphon to be positioned in the bore passage. The return pipe in such cases should also be flexible so as to accomodate the flexibility of the enclosure.

The collection means is preferably an annular channel provided around the periphpery of the interior of the enclosure. The term annular refers not only to a circular formation but also to other formations, such as rectangular.

Advantageously, the aperture either forms or carries a nozzle to increase the 15 kinetic energy of the vapour stream. The nozzle may also be used to direct the vapour stream at an optimum angle onto the blades of the turbine to improve efficiency.

The turbine may be coupled to an electrical generator. If the electrical generator is located outside the enclosure a shaft or similar means associated s. with the turbine will be required to drive the generator. Difficulties in sealing the enclosure may result due to the pressures within the enclosure and, accordingly, the electrical generator is preferably located within the enclosure.

The power produced by the generator may then be easily transferred to the exterior through a sealed gland.

Alternatively, or in addition to electrical power, mechanical power may be transferred out of the enclosure using a magnetic coupling between the turbine and an external device driven by the turbine.

The invention will now be further described by way of example only with reference to the accompanying drawing, the sole figure of which is a cross 910517,pavOI.techn.s,4 sectional view of a thermosyphon in accordance with a preferred embodiment of the invention.

Referring to the figure, the thermosyphon of the preferred embodiment comprises a substantially vertical elongate enclosure 1 preferably of cylindrical form and comprising an evaporator section A containing a working liquid reservoir 2 at its lower end, a condenser section C at the upper end, and an adiabatic section B disposed between the evaporator section A and the condenser section C. To minimise potential heat losses in the adiabatic section B it may be provided with thermal insulation 3.

S.

An annular condensate collection channel 9 is provided around the inner periphery of the cylinder. A separator plate 5 is disposed below the channel 9 between the condenser section C and the adiabatic section B. The diameter of 15 the separator plate 5 is the same as the diameter of the enclosure 1. The plate has one or more apertures which either form or carry nozzles 7 which provide passageways through which a vapour stream may flow. The separator plate 5 has the effect of supporting the pressure difference between the evaporator section A and the condenser section C and enabling high velocity flow out of the nozzles 7.

A turbine 13, directly coupled to an electrical generator 15, is axially mounted downstream of the separator plate 5. The diameter of the turbine 13 should be such that condensed vapour can drain freely past the turbine 13 into the channel9.

Extending from the bottom of the channel 9, through the separator plate 5 and terminating in the evaporator section A are one or more liquid return pipes 11. These return pipes 11 transport condensed vapour from the channel 9 to the liquid reservoir 2.

910517,pawOO.techrspe, Heat is supplied to the evaporator section A from a suitable energy source and is absorbed by the working liquid. A solar pond can provide a relatively low cost means of collecting solar energy, and could be used as a heat source for the thermosyphon. Thermal energy generated by other types of solar collectors can also be used. Geo-thermal energy and waste heat can also be used as heat sources. As the liquid vaporises the heat is taken up as latent heat of vaporisation. The vapour then expands adiabatically in the nozzles 7 from the high pressure and temperature at the evaporator section A to the lower pressure and temperature at the condenser section C where it cools and condenses. The speed achieved by the vapour stream at the nozzle exit is dependent on the pressure difference between the evaporator section A and the condenser section C, and in some instances may reach the speed of sound.

As the vapour stream expands through the nozzles 7 its kinetic energy, and 15 hence its speed, increases. The shape and size of the nozzles are chosen to maximise the increase in kinetic energy. The vapour, with its speed increased by the passage through the nozzles 7, impinges on the blades of the turbine 13 and provides a force which rotates the turbine, which in turn drives the generator 15. The nozzles 7 are arranged to direct the vapour stream onto the turbine blades at the optimum angle required to produce the maximum electrical power extraction. The generator 15 is located within the thermosyphon, and is provided with conducting wires, which exit the thermosyphon through a sealed gland, to conduct the generated current to the exterior of the thermosyphon. The loss in energy resulting from the work done 25 on the turbine by the vapour stream may cause some of the vapour to condense, and the cyclone action of the turbine 13 separates this liquid from the vapour. This liquid collects in the channel 9 and combines with the liquid draining from the condenser section C. The combined liquid is then returned to the evaporator section A via the return pipe 11, and the cycle is repeated.

910517,pavM1.technspe,6 0 1, -7- The hydrostatic pressure head in the return pipes 11 must be such that it maintains the flow of liquid from the lower pressure condenser section C to the higher pressure evaporator section A, with the return rate of the liquid matching the evaporation rate. The configuration of the return pipes should be such that vapour or liquid from the evaporator section A is prevented from flowing through the pipes. In the embodiment shown this is provided by a Ushaped portion at the lower end of each pipe. Alternatively, the return pipes may be provided with a non-return valve. The return system is gravity based.

The difference in height between the free surface of the returning liquid and the upper surface of liquid reservoir 2 should be greater than the required hydrostatic head in pipe 11 to compensate for the pressure difference between the evaporator section A and the condenser C and also to overcome the fluid friction losses in pipe 11.

«o oo 15 The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

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910517,pawOO1.techn.spe,7

Claims

1. A thermosyphon comprising an enclosure containing a vaporisable material, said enclosure comprising an evaporator section at a lower end portion wherein the material is heated and vaporised, an adiabatic section through which the vapour flows, a condenser section at an upper end portion wherein the vapour condenses, collection means to collect the condensate, at least one return pipe to return the condensate from the collection means to the evaporator section, separator means separating the evaporator section from the condenser section to thereby, in use, provide a differential pressure therebetween, the separator means having at least one aperture for flow therethrough of the vapour, and a turbine mounted downstream of the separator means to be driven by the vapour stream flowing through the aperture.

2. A thermosyphon according to claim 1, wherein the enclosure is substantially rigid.

3. A thermosyphon according to claim 1, wherein at least a portion of the enclosure other than that adjacent the turbine is flexible.

4. A thermosyphon according to any one of the preceding claims, wherein the collection means is adjacent the separator means.

5. A thermosyphon according to any one of the preceding claims, wherein the separator means is above the adiabatic section.

6. A thermosyphon according to any one of the preceding claims, wherein the collection means comprises an annular channel open towards the condenser section provided around the periphery of the interior of the enclosure. 910517,pav.O1.technspe,8 -9-

7. A thermosyphon according to claim 5 or claim 6, wherein in separator means is of plate like form.

8. A thermosyphon according to any one of the preceding claims, wherein the aperture either forms or carries a nozzle to increase the kinetic energy of the vapour stream.

9. A thermosyphon according to any one of the preceding claims, wherein the return pipe is configured so as to prevent the vapour or liquid from the evaporator section from flowing therethrough. b a..

10. A thermosyphon according to claim 8, wherein the lower end of the return pipe is U-shaped.

11. A thermosyphon according to any one of claims 1 to 8, wherein the return Spipe is provided with a non-return valve so as to prevent the vapour or liquid from the evaporator section from flowing therethrough.

12. A thermosyphon according to any one of the preceding claims further Scomprising an electrical generator located within the enclosure and coupled to the turbine.

13. A thermosyphon according to any one of the preceding claims, wherein the turbine is magnetically coupled to an external device to transfer mechanical power out of the enclosure. 910517,pav0l.technspe,9 10

14. A thermosyphon subtsantially as hereinbefore described with reference to the accompanying drawing. The stepso fea:tures discloged herein or ancmbination Uh '~reor. a a, a a -a B a.. I *8~ DATE-D this 17th day of May, 1991. TECHNISEARCH LTD. By its Patent Attorneys DAVIES COLLISON a' 910517,pawOO Ltechnspe, -11 ABSTRACT A thermosyphon comprising a substantially elongate enclosure (1) having an evaporator section wherein a vaporisable material is heated and vaporised, an adiabatic section through which the vapour flows and a condenser section in which the vapour is cooled and condenses. A separator plate having a nozzle separates the evaporator section (A) from the condenser section and increases the kinetic energy of the vapour *stream. A turbine (13) activated by the vapour stream drives a generator The condensate from the condenser section collects in an annular channel and is returned via return pipe (11) to the evaporator section e C ,i 0 O*t** 910515,pa'vOOLtecnrspe,11