TED-AJ03-578 DEVELOPMENT OF A TOP-HEAT-MODE LOOP THERMOSYPHON

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Thermosyphons are heat transport devices that can transport a large amount of heat using body forces (e. g. gravitational and centrifugal forces) in the opposite direction to their forces. Thus, they can work without any external power supply, and have very simple structures and a function for rectifying heat flow (i. e. limiting heat flow to one direction). However, the third characteristic may become disadvantage for the following applications; melting snow on road and building air conditioning using solar energy. Thus, thermosyphons cannot be used in such applications, and the heat transport device that can transport a large amount of heat to the same direction as the body forces (i.e. heat is transported from top to bottom positions if the body force is gravitational force) is required. It is so called "top-heat-mode heat pipe". Up to now, capillary pumped loop type [1-2], bubble pumped type [3] and osmosis type heat pipes [4-6] have been proposed as the top-heat-mode heat pipe. However, they have the following problems; (1) They have a complex structure, (2) The operation is easy to be in an unsettled state at lower heat input or after the end of supplying heat into the heating section, (3) The durability and reliability are poor, i. e. due to generation of non-condensable gas or deterioration of working fluid and organic permeable membrane, (4) Some external power supply is required, etc. Therefore, in order to overcome these problems, we have tried to develop a new type heat pipe, referred as a top-heat-mode loop thermosyphon. The top-heat-mode loop thermosyphon is a sensible-heat transport device with a bubble pump but without external power supply, and is mainly consist of an evaporator, a heat exchanger and a cooler, which are connected together via pipes in such a way as to form a continuous loop. In the present study, the prototype device made of brass tube with length of about 36m and inside diameter of 8mm was manufactured, of which the heat transport height is about 2m. The experimental apparatus tested to obtain the heat transport rates, the temperature along the loop and the circulation flow velocity under several experimental conditions, using water and ethanol as the working fluid. As a result, the apparatus could transport heat up to 2250 W for water and 480 W for ethanol, at the temperature of liquid in the cooler of 30℃. The circulation flow velocity first increased and then decreased slightly with an increase in heat input, but was independent of the temperature of the liquid in the cooler. The present apparatus is found to have the fluctuation of the circulation flow velocity at the lower heat input and the lower temperature of the liquid in the cooler due to subcooled boiling in the heating section of the evaporator, but the fluctuation was relatively small. The effective thermal conductivity is about 8×1(0)^5 W/(m・K) for water, and is about 2×(10)^5 W/(m・K) for ethanol, which is remarkably larger than that of high thermal conductive materials. The maximum heat transport rate and the effective thermal conductivity are found to be dependent on the circulation flow velocity and specific heat of the liquid. Finally, the top-heat-mode thermosyphon proposed in the present study is found to be an extremely promising device as the top heat mode heat pipe, and is expected to have wide application in various industries in the near future.

TED-AJ03-578 DEVELOPMENT OF A TOP-HEAT-MODE LOOP THERMOSYPHON

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