Stoves and furnaces – Solar heat collector – With control means energized in response to actuator...
Patent
1992-01-16
1993-09-07
Davis, Jr., Albert W.
Stoves and furnaces
Solar heat collector
With control means energized in response to actuator...
126599, 165 32, F24J 240, F24J 232
Patent
active
052419509
DESCRIPTION:
BRIEF SUMMARY
This invention relates in general to a heat pipe device, and in particular to such a device for use in solar radiation collectors.
A heat pipe transfers and distributes heat by vaporisation and condensation of a working fluid which is employed as a heat transfer medium. A principal feature of a heat pipe is that the energy required for the flow of the liquid and the vapour in the device, in the presence of gravity, is completely provided by the heat source, so that no external pumping means is needed.
Solar radiation collectors are intended to convert solar radiation into heat in the working fluid and to transfer the heat, with the maximum possible efficiency, to a secondary heat transfer fluid, which may be water or air, for example. The use of heat pipes in solar collectors is already known from my British Patent number 2023804 and from my British Patent application number 2023803, for example.
A heat pipe conventionally comprises an evaporator element and a condenser element interconnected by means of a conduit, the condenser being placed in use above the evaporator. When the device is cool the working fluid collects in the base of the evaporator. When heat is supplied to the evaporator the working fluid begins to vaporise and moves up into the condenser, where the heat is removed from the vapour, the vapour then condenses and falls back into the evaporator under the force of gravity.
If, however, heat is not removed from the condenser, or it is not removed at a high enough rate, the condenser will overheat and the device may be damaged. Safety measures therefore have to be included in the device to prevent this. It is desirable to devise a means whereby the maximum temperature of the condenser may be limited to a chosen temperature T.sub.o. This can be achieved if the working fluid is collected in the condenser compartment when the condenser reaches the limiting temperature T.sub.o, rather than allowing the fluid to return to the evaporator. As a consequence, if heat continues to be applied to the evaporator, it gradually dries out and all the working fluid is held in the condenser, so that heat transfer between the evaporator and the condenser is interrupted.
International Patent Application number WO87/07003 describes a heat pipe in which, during normal operation, the condensed working fluid is drained or diverted back into the evaporator to continue the cycle of heat transfer, but if the condenser temperature goes above T.sub.o, regulating means are provided for collecting the condensed working fluid in a chamber whereby the fluid cannot return to the evaporator. The regulating means comprises a valve controlled by a means made from a shape memory alloy, the alloy being arranged to alter its shape when it reaches the limiting temperature T.sub.o.
The regulating means of WO87/07003 requires a relatively large force to operate the valve in order to guarantee a proper seal when the valve is in its closed position. Furthermore, the valve needs to be precisely machined and fitted to ensure a good seal, and the sealing surfaces may be susceptible to damage during use. Thus a heat pipe employing this regulating means is difficult and expensive to produce.
According to the present invention there is provided a heat pipe containing a working fluid, the heat pipe comprising an evaporator, a condenser, an interconnecting tube joining the evaporator and the condenser, and a regulating means for limiting the maximum temperature in the condenser to a predetermined temperature, the regulating means comprising a plug operable by means of a temperature sensitive member to move between a first position in which the plug seats in a fluid reservoir in the condenser and a second position in which the reservoir is adapted to collect the working fluid.
Preferably the fluid reservoir is formed by means of an overflow pipe which extends into the condenser from the base of the condenser. The plug may then be an annular member adapted to fit slidingly over the overflow pipe.
The temperature sensitive member is preferably made
REFERENCES:
patent: 1705550 (1929-03-01), Vernet
patent: 4305382 (1981-12-01), Nott
patent: 4941526 (1990-07-01), Nilsson
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