Analysis Evaluation of Downhole Heat Exchanger for the promotion of Geothermal Energy Utilization

点击翻译按钮获取中文摘要

Several types of downhole heat exchangers, for example thermosyphon type heat pipe, concentric tube thermosyphon, U-tube downhole heat exchanger, coaxial downhole heat exchanger, as well as others, have been proposed in order to extract heat directly from shallow geothermal resources. Among these downhole heat exchangers, the U-tube downhole heat exchanger is widely used in Japan as well as around the world, because of its cost performance and easy construction. Another reason it is used is because it has been reported that highly efficient heat extraction can be achieved with the downhole coaxial heat exchanger through its reverse circulation mode of working fluid in heat extraction process.The aim of this study is to estimate the heat extraction and heat release performance of the geothermal heat exchangers including single, double and triple U-tube heat exchangers and downhole coaxial heat exchangers by experiments and computer simulation.From the experimental results it was found that increasing both the flow rate and inlet temperature of the working fluid of the heat extraction increases the heat release rate with a single U-tube heat exchanger. Furthermore, the comparison of the heat extraction performance between double and triple U-tube downhole heat exchangers was made by three-dimensional numerical calculation, The finding revealed that the heat extraction rate using a triple U-tube downhole heat exchanger is greater than that using a double U-tube under a fixed flow rate of the working fluid of heat extraction. In the case of downhole coaxial heat exchanger, it was found from the computer simulation that heat extraction performance greatly depended on the factors of the inner tube material, length of heat exchanger and circulation modes of working fluid of heat extraction.