| Abstract: |
The heat transfer rate by a heat pipe is limited by four reasons when it is placed in a geothermal system (1) the characteristics of the heat pipe, including the density, heat capacity and the amount of the working fluid, the radius, and the length of the heating zone(Evapo rator) • (2) the efficiency of heat supply from the geothermal system. (3) the temperature differece between the heating zone and the cooling zone(condenser). (4) heat insulation between the evaporator and the condenser. Shiraishi(1986) has reported the heat transfer limit caused by the first reason above. He extended the experimental formular of Nejat(1981) to super-scaled heat pipes, and calculated the effect of the amount of working fluids, the diameters, and the length of the evaporators on the limit .heat transfer rate. Kimura et al (1987, 1988a, 1988b) examined the second reason for geothermal systems where reservoir water flows through the porous media near the heat pipe. They assume that the surface temperature of the evaporator of a superscaled heat pipe be constant, and they estimate the heat transfer rate analytically and numerically at the cases when reservoir fluid flows vertically or horizontally and when natural convection occurs in the reservoir. In this report, we investigate the effects of the factors listed in (2), (3), and (4) for geothermal systems without fluid flow. Experiment wa.~ carried out both in laboratory and in geothermal field with a short heat pipe. A numerical conduction model is given to analyze the temperature distribution. The purpose of this report is to make clear the problems l,hich would be encoutered in utilizing heat pipe to extract heat energy, therefore, to present guidelines to further reaserches using longer heat pipe in actual field in the future. |