A super-long flexible heat pipe (SFHP) with the total length up to 32m is experimentally tested in this work to evaluate its potential for geothermal utilization in Nanjing, China. Its evaporator section, fabricated by metal bellows, is 30m long and vertically installed in a ground drilling. The temperature response and heat transfer characteristics of SFHP were investigated. The results show that the underground temperature at the depth larger than 10m is stable in the range of 17-18â„ƒ throughout the year. SFHP starts to operate upon the temperature at the wall of condensation section falls below 15â„ƒ. The heat transfer power of SFHP increases with decreasing temperature of cooling water. The variation of cooling water flow rate has an insignificant influence on the heat transfer power of SFHP, however its effect on the total thermal resistance is remarkable. In tests, the maximum heat transfer power is about 168.3W when the flow rate of cooling water is controlled at 600ml/min and the average temperature at 8.5â„ƒ. In addition, the higher the flow rate of cooling water, the shorter the start-up time.
Keywords Super-long flexible heat pipe, Geothermal utilization, Temperature response, Heat transfer characteristic