Investigation on warming the surface ground temperature in winter using heat pipes

Abstract

A series of performance and demonstration tests was conducted in this investigation on warming the surface ground temperature in winter using heat pipes (HP). HP transferred underground heat from the lower layer to the surface layer, promoting agricultural crop growth. Performance tests were carried out using water, acetone, and refrigerant (CFC alternative, R134a) as working fluids, investigating their suitability for winter ground temperature conditions. The results indicate that filling the HP with 3 % of the inner volume of refrigerant is an effective heating device. In the demonstration test, a 2-m HP was buried, and temperature comparisons were made at a depth of 15 cm with and without the HP. The temperature at 15 cm depth without the HP was about 2 ℃. With HP, the temperature near the HP was about 8 ℃. Although the thermal source successfully increased temperatures in the surface layer, it was observed that the effect of soil temperature rise was suppressed only by a few centimeters away from the HP.