WO2009124345A1

WO2009124345A1 - A heat pipe and a water heater using a heat pipe

Info

Publication number: WO2009124345A1
Application number: PCT/AU2009/000430
Authority: WO
Inventors: Brendan Vincent Bourke
Original assignee: Rheem Australia Pty Limited
Priority date: 2008-04-10
Filing date: 2009-04-08
Publication date: 2009-10-15

Abstract

A heat pipe adapted for use in a water heating system includes a cylindrical heat pipe affixed to an attachment plate. A first part of the pipe is located on one side of the late, and the second part of the pipe is located o the other side of the plate. The axis of the pipe is inclined to the plane of the plate so that, when heat is applied to the working fluid in the lower portion of the pipe, the working fluid vapourizes. The working fluid condenses in the upper portion as the working fluid condenses due to heat transfer through the wall of the pipe. The condensed working fluid runs back to the lower portion of the pipe.

Description

A Heat Pipe and a Water Heater Using a Heat Pipe

Field of the invention

[001] This invention relates to heat pipes and to water heaters using heat pipes.

[002] The invention is particularly suited for water heating systems and can be adapted for use as a replacement for electrical elements in hot water tanks.

Background of the invention

[003] A heat pipe is basically an evacuated tube which is partially filled with an evaporable heat transfer fluid. The pipe is evacuated to reduce the amount of non-condensing gas, as this gas will reduce the efficiency of the heat pipe. The lowering of the pressure in the tube lowers the evaporation temperature of the fluid. Heat pipes can be used for heat transfer for cooling or heating.

[004] US3854454 discloses a water heating system using a gas heated heat pipe to heat water in s tank. The heat pipe is an "L" shaped tube, with the foot of the "L" fitted with heat absorbing fins and the leg of the "L" fitted with heat distributing fins. The leg is inserted into the base of a hot water tank. The fins on the foot are heated by a gas flame positioned underneath the tank. This system is a purpose-built heat pipe hot water system. An "L" shaped heat pipe is complex to manufacture. The fins on the leg of the pipe require a hole in the base sufficiently large to admit the fins into the tank. The system cannot readily be retro-fitted to an existing electrically heated water heating system.

[005] It is desirable to provide a heat pipe which is less complex to manufacture than the "L" shaped heat pipe.

[006] It is desirable to provide a heat pipe which can be readily fitted to a tank.

[007] It is also desirable to provide a heat pipe which can be retro-fitted to an installed water heater tank.

[008] A further application of the present invention is to enable the use of gas heating in a low input energy, slow recovery system such as a 5 to 10 MJ input. Summary of the invention

[009] The present invention provides a heat pipe and a heat pipe water heating system which meets one or more of the above requirements.

[010] According to an embodiment of the invention, there is provided a heat pipe arrangement including a heat pipe sealingly affixed to an attachment plate.

[011] The axis of the heat pipe can be affixed at an incline to the plate.

[012] A first portion of the pipe can protrude from a first side of the plate.

[013] A second portion of the pipe can protrude from a second side of the plate.

[014] The plate can be formed to conform to the wall of a tank.

[015] The plate can include an attachment arrangement adapted to enable the plate to be attached to a tank.

[016] The pipe can be partially evacuated and can contain a heat transfer fluid.

[017] The volume of heat transfer fluid can be of the order of 10% to 15% of the volume of the pipe.

[018] The heat pipe arrangement can include an array of heat transfer fins attached to the lower portion of the pipe.

[019] The heat pipe arrangement can include an electrical heating element inside the lower portion of the pipe.

[020] The invention also provides a water heating system including a heat pipe arrangement.

[021 ] In the water heating system, the heat pipe can be adapted to be heated by gas, the system including a gas burner arranged to heat the heat pipe, a temperature sensor adapted to provide an indication of the temperature of water in the tank, and a gas valve responsive to the sensed temperature to control the flow of gas to the burner.

[022] The water heating system can include a solar water heating arrangement.

[023] The invention also provides a method of retro-fitting a heat pipe arrangement to a water heater tank. Brief description of the drawings

[024] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[025] Figure 1 is schematically illustrative of an electrically heated water heating system;

[026] Figure 2 is schematically illustrative of an embodiment of the present invention in the form of a heat pipe water heating system;

[027] Figure 3 is schematically illustrative of details of a heat pipe installed on the side of a water tank;

[028] Figure 4 is schematically illustrative of a heat pipe arrangement according to an embodiment of the invention;

[029] Figure 5 is a front view of the arrangement of Figure 4;

[030] Figure 6 is schematically illustrative of a combined solar and heat pipe water heating system;

[031 ] Figure 7 is schematically illustrative of a further embodiment of the invention;

[032] Figure 8 is schematically illustrative of a plate suitable for use in the embodiment of Figure 7.

[033] Figure 9 illustrates an alternative gas boosted solar water heater using a heat pipe input;

[034] Figure 10 illustrates an alternative shape for a heat pipe;

[035] Figure 11 illustrates a twin heat pipe arrangement.

[036] Figure 12 schematically illustrates a curved heat pipe installed in a tank;

[037] Figure 13 schematically illustrates a spiral heat pipe installed in a tank;

[038] Figure 14 illustrates a thermostat arrangement adapted for use with the present invention.

[039] The numbering convention used in the drawings is in the form "n.nnn" or

"nn.nnn" where the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements.

Detailed description of the embodiment or embodiments

[040] The invention will be described with reference to the embodiments shown in the drawings.

[041] Figure 1 schematically illustrates a hot water system including a tank 1.002 and an electrical heating element 1.004. the electrical heating element enters the tank through an aperture in the side wall of the tank which is sealed by an appropriate sealing arrangement including a support plate 1.005 welded to the tank wall and carrying stub bolts 1.007. The bolts 1.007 pass through holes in mounting plate 1.011 which carries the electrical element 1.004 and insulator 1.001. Nuts 1.009 fasten the mounting plate 1.011 to the support plate 1.005. A gasket seals the interface between the mounting plate 1.011 and the support plate 1.005. The leads of the electrical heating element pass through the sealing arrangement via an insulator. Cold water can be delivered to the tank at a point located near the bottom of the tank via pipe 1.050, and heated water can be drawn from the tank at a point located near the top of the tank via pipe 1.052.

[042] Figures 2, 3, 4, & 5 illustrate schematically an embodiment of the invention in which a heat pipe 2.010 is inserted into a tank 2.002 via an aperture in the side wall of the tank 2.002. The aperture is sealed by the sealing arrangement including attachment plate 2.006 and support plate 2.005 in a similar manner to that shown in relation to Figure 1. The heat pipe 2.010 passes through an aperture in the mounting plate 2.006 and is sealingly attached thereto by, for example silver soldering. A first part 2.012 of the heat pipe 2.010 is outside the tank and a second part 2.014 of the heat pipe 2.010 is inside the tank. The heat pipe 2.010 is inclined to the horizontal.

[043] Where the heat pipe is metal, such as copper, there is a likelihood of galvanic corrosion. Accordingly the portion 2.014 of the heat pipe inside the tank is treated to inhibit this corrosion by, for example, applying a heat shrink coating.

[044] In an alternative arrangement, the heat pipe may be made from a combination of materials, such as metal for the lower portion 2.012, and glass for the upper portion 2.014. However, the use of glass will entail additional design complexities to ensure that the tube is capable of withstanding the thermal cycling stresses, and in the case of a combined pipe structure, glass to metal sealing.

[045] The heat pipe 2.010 is evacuated to a low pressure, and contains about 10 to 15 % by volume of the heat transfer fluid in liquid form at room temperature. Then a mount of residual air in the heat pipe should be kept as low as possible. Any residual air in the heat pipe can reduce the efficiency of the heat pipe, as the air does not undergo the condensation at the operating temperature of the water heating system.

[046] Various fluids can be used for the heat transfer fluid, including water, alcohol, and other refrigerant heat transfer fluids. Suitable materials for the heat pipe include copper, and aluminium. The pipe must be of sufficient strength to withstand the pressure differentials between its cooled state and its heated state, as well as thermal cycling stresses. A typical heat pipe may be designed to withstand pressures of the order of 1400 kPa.

[047] In one embodiment, water is used as the heat transfer fluid and the heat pipe is made of copper.

[048] When the heat pipe is installed at an incline, the heat transfer fluid in a liquid state collects in the lower portion of the heat pipe. The pipe can be inclined between 15°and 80° to the horizontal. Preferably, the pipe is inclined between 25° and 60°. Heating means (not shown in Figure 2) are applied to cause evaporation of the heat transfer fluid, so that the evaporated heat transfer fluid rises towards the upper portion of the heat pipe where it is condensed by the water in the tank. The gaseous heat transfer fluid looses its latent heat of condensation and collects in liquid form on the walls of the heat pipe. Because the pipe is inclined, the condensed heat transfer fluid flows down to the lower portion of the heat pipe.

[049] In the embodiment shown in Figure 3, the heat pipe is heated by gas.

[050] The heat pipe 3.010 is a substantially cylindrical pipe with sealed ends and containing an amount of heat transfer fluid 3.015 in liquid form in the lower portion of the inclined pipe.

[051 ] The lower portion 3.012 of the heat pipe is external to the tank 3.002 and is heated by a gas burner 3.018. Heat fins 3.016 are affixed to the lower portion 3.012 of the pipe 3.010. In the embodiment shown, the fins 3.016 are formed to contact the pipe only in the vicinity of the liquid heat transfer fluid. Thus, at least some of the fins do not completely enclose the pipe 3.010. However, the fins can alternatively be formed so each fin has a closed contact line with the pipe 3.010.

[052] Also shown in Figure 3 is a temperature sensor 3.032 which, in practice is positioned to measure the temperature of the water or the temperature of the wall of the tank at a to provide an indication of the temperature of the water. The temperature sensor 3.032 is connected to a controller 3.030, to which a gas control valve 3.034 in the gas line 3.020 is also connected. Thus the controller 3.030 can control the flow of gas to the burner 3.018 in response to the temperature sensor 3.032. The valve 3.034 can be an ON/OFF valve, or it can be a continuously variable control valve enabling control of the amount of heat applied to the heat pipe. Electronic ignition means (not shown) can also be provided to ignite the gas when the valve 3.034 is opened, or a pilot flame (not shown) can be provided.

[053] A housing 3.022 is attached to enclose the gas burner and heat fins, while admitting air. The housing 3.022 can also have provision to duct the combustion products to an exhaust.

[054] Figures 4 & 5 illustrate a heat pipe arrangement according to an embodiment of the invention. The heat pipe 4.010, 5.010 passes through an aperture in plate 4.006, 5.006 and is sealed thereto by, eg, brazing, welding, soldering, adhesive or other suitable means to form a water tight seal. The plate 4.006 is adapted to be affixed to the tank to provide a water tight connection. For example, the plate 4.006 can be provided with holes 4.007 to receive the bolts 1.007 bolts which attached to the wall of the tank. A seal can be provided between the plate and the tank wall.

[055] Figure 6 illustrates schematically a water heating system using both solar heating and a gas heated heat pipe. A solar collector 6.040 includes an upper header 6.042 and a lower header 6.044 and an array of solar collector tubes 6.046 connecting the upper and lower headers. The solar panel shown is a direct solar panel which directly heats the potable water, rather than by an indirect solar heating system in which the water is heated through the agency of an intermediate heat exchanger and a heat transfer fluid in a closed circuit through the solar panel. However, an indirect solar system could also be used with the present invention. [056] The upper header 6.042 is connected to the upper region of the tank 6.002 via pipe 6.048, and the lower header is connected to a lower portion of the tank 6.002 via pipe 6.049. hi the embodiment shown, the pipe 6.049 is connected between the top and bottom of the tank 6.002 so only a portion of the water in the tank is heated by the solar panels.

[057] A heat pipe 6.010 is inserted into the tank near the base of the tank. The lower portion of the heat pipe projects externally of the tank and can be used to inject heat into the heat pipe, for example by heating with gas as described in relation to Figure 3. Other means of heating the heat pipe can also be used.

[058] In the arrangement shown in Figure 6, the heat pipe can be used to boost the solar water heating system, and can thus compensate for low sunlight periods or for periods of heave demand for hot water.

[059] A control arrangement such as that of Figure 3 can also be used with the system of Figure 6.

[060] Figures 7 & 8 illustrate schematically a further embodiment of the invention in which the heat pipe 7.010 is heated internally using an electrical element 7.070. In this example, because the heat pipe does not need to protrude beyond the periphery of the tank, it is possible to provide a flush or recessed mounting which does not require additional exterior space. The heat pipe can be mounted on a concave plate 7.006, with the electrical leads 7.072 projecting from the plate 7.006. The electrical element 7.070 in this case operates at a lower temperature and in a less hostile chemical environment because the sealed heat pipe is partially evacuated, and the element is exposed to the same heat transfer fluid. The recessed plate 8.006 is illustrated schematically in Figure 8. It has a peripheral flange 8.082 which can include through holes for bolts attached to the wall of the tank, a frusto-conical recessed portion 8.084, and a central portion 8.086 with heat pipe mounting aperture 8.088. Because the heat pipe is inclined, the aperture 8.088 may be elliptical.

[061] The heat pipe can have a circular cross section, hi a further embodiment the cross section of the heat pipe can be oval or elliptical. One or more heat pipes can be used with a tank.

[062] The operation of the heat pipe is illustrated in Figure 3, where the heat transfer fluid in liquid form collects in the lower portion 3.012 of the heat pipe. This lower portion 3.012 is heated by the gas burner 3.018 and the heat transfer fluid evaporates to its gaseous form as illustrated at 3.017, and this gaseous heat transfer fluid rises into the upper portion 3.014 of the heat pipe. This upper portion 3.014 is inserted into the tank of the water heater, and the heat is drawn from the upper portion of the heat pipe by the water in the tank. This results in the condensation of the heat transfer fluid gas which condenses on the walls of the upper portion 3.014 and runs back to the lower portion 3.012 in a continuous cycle as indicated by looped arrows 3.021.

[063] Preferably the gas flame impinges on the heat pipe in a region which is continuously filled with heat transfer fluid. Because the heat pipe is tilted, the liquid heat transfer fluid forms a wedge shaped pool having a "shallow end" and a "deep end". The fluid at the shallow end will thus evaporate more readily as it has a larger surface/volume ratio in contact with the pipe.

[064] The heat pipe arrangement of the present invention can be adapted for retro- fitting to an electrical heater by ensuring that the heat pipe will fit through the existing aperture in the tank wall provided for the insertion of the electrical heating element. Thus, in one embodiment, the upper portion of the heat pipe does not include fins to distribute the heat to the water in the tank, relying instead on the heat transfer through the walls of the upper portion 3.014.

[065] Figure 9 illustrates a water heating system having a solar collector arrangement

9.040 connected to heat a lower portion of the tank 9.002 as indicated by the outlet pipe 9.049 via which water from near the bottom of the tank is drawn to the lower header 9.044 of the solar collector, and heated water is returned to an intermediate point of the tank via pipe 9.048. A heat pipe having an exterior heat input portion 9.012 and an internal heat delivery portion 9.014 is located to heat the water in the upper portion of the tank 9.002. This arrangement is suitable for a low energy low recovery system using gas to heat the heat pipe. It is also suitable for retro-fitting to an electrically boosted solar water heating system.

[066] Figure 10 illustrates a further embodiment of a heat pipe according to an embodiment of the invention in which the heat pipe 10.010 is of an arcuate shape having an external portion 10.012 which can be heated by gas, and an internal portion 10.014 via which heat can be delivered to the4 water in the tank. The interior portion can be extended in length compared with the straight heat pipe, as shown in Figure 12. This provides increased heat transfer surface area. The lower portion of the heat pipe can have an angle of about 25° to the horizontal and the upper portion can have an angle of about 60°.

[067] In a further embodiment shown in Figure 11 , twin heat pipes 11.010, 11.013 are provided, again increasing the heat transfer surface compared with a single heat pipe.

[068] Figure 13 illustrates schematically a spiral heat pipe 13.010 installed in the upper portion of a tank 13.002. The spiral coils can be inserted through an aperture in the tank wall, such as an existing electrical element aperture or "purpose-built" aperture, by inserting the leading edge of the spiral heat pipe coli and then turning the heat pipe in a corkscrew manner to feed the spiral coils into the tank. As discussed in relation to Figure 9, this arrangement can be used in conjunction with a solar collector arrangement having inlet pipe 13.048 and outlet pipe 13.049, or it can be used in a stand alone heater arrangement, in which case, the heat pipe would be installed in the lower portion of the tank.

[069] Figure 14 illustrates a thermostat arrangement adapted for use with the present invention. A fluid filled bulb 14.056 is attached to the outside of the tank 14.002, for example by the use of a mounting plate 14.058. The mounting plate can be attached to the tank by spot welding, thermally conductive adhesive, or other suitable means. The bulb contains a fluid which is chosen to provide a step function output via fluid pipe 14.060 to the gas valve 14.034, at the desired temperature, or, drives a snap-action mechanism at the gas valve 14.034 set to operate at the chosen temperature. SIT provide a thermostat bulb (Model 630) arrangement in which the bulb can be located at a separate location from the gas valve. In an embodiment of the invention, such as in the case of retrofitting the heat pipe to an existing tank, the bulb can be attached to the outside of the tank. The tank is enclosed in insulation, so the tank wall will be at approximately the same temperature as the water in the tank at the same height as the bulb.

[070] hi an alternative arrangement, the bulb can be held directly in contact with the tank wall by a thermally conductive glue, by a strap encircling the tank, or by other suitable means.

[071] As discussed in relation to Figure 3, external fins can be used to increase the heat transfer area of the gas to the heat pipes. Internal fins can also be added to the inner portion of the heat pipes to further increase the heat transfer area. [072] In one embodiment, the heat pipes have a diameter of the order of 15mm, the length of the internal portion can be of the order of from 300mm to 500mm, and the external portion can be of the order of 150mm long.

[073] The gas burner can be a natural draft burner or a forced draft burner.

[074] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated.

[075] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[076] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

[077] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. A heat pipe arrangement including a heat pipe sealingly affixed to an attachment plate.

2. A heat pipe arrangement as claimed in claim 1, wherein, in use, the axis of the heat pipe is affixed at an incline to the horizontal.

3. A heat pipe arrangement as claimed in claim 1 or claim 2, wherein a first portion of the pipe protrudes from a first side of the plate.

4. A heat pipe arrangement as claimed in any one of the preceding claims, wherein a second portion of the pipe protrudes from a second side of the plate.

5. A heat pipe arrangement as claimed in any one of the preceding claims, wherein the plate is formed to conform to a mounting arrangement on a tank.

6. A heat pipe arrangement as claimed in any one of the preceding claims, wherein the plate includes an attachment arrangement adapted to enable the plate to be attached to a tank.

7. A heat pipe arrangement as claimed in any one of the preceding claims, wherein the pipe is partially evacuated and contains a heat transfer fluid.

8. A heat pipe arrangement as claimed in claim 9, wherein the volume of heat transfer fluid is of the order of 10% to 15% of the volume of the pipe.

9. A heat pipe arrangement as claimed in any one of the preceding claims, including an array of heat transfer fins attached to the lower portion of the pipe.

10. A heat pipe arrangement as claimed in any one of claims 1 to 8, including an electrical heating element inside the lower portion of the pipe.

11. A water heating system including a heat pipe arrangement as claimed in any one of the preceding claims.

12. A water heating system as claimed in claim 11, wherein the heat pipe is adapted to be heated by gas, the system including a gas burner arranged to heat the heat pipe.

13. A water heating system as claimed in claim 12 including a temperature sensor adapted to provide an indication of the temperature of water in the tank.

14. A water heating system as claimed in claim 13, including a gas valve responsive to the sensed temperature to control the flow of gas to the burner.

15. A water heating system as claimed in any one of claims 11 to 14, including a solar water heating arrangement.

16. A water heating system as claimed in claim 15, wherein the solar collector is connected to provide heating to water in a lower portion of the tank, and the heat pipe arrangement is located to heat water in an upper portion of the tank.

17. A heat pipe arrangement substantially as herein described with reference to the accompanying drawings.

18. A water heating system substantially as herein described with reference to the accompanying drawings.

19. A method of retro- fitting a heat pipe arrangement to a water heater tank substantially as herein described with reference to the accompanying drawings.