Performance Study on U-tube Downhole Heat Exchanger Geothermal Systems with Various Working Fluids and Configurations

Abstract

The downhole heat exchanger (DHE) geothermal system is suitable for exploitation of medium-low temperature geothermal resources, which has been widely used in space heating for residential and/or small-scale commercial buildings. The heat extraction performance of a U-tube DHE system with different working fluids remains unclear. In this paper, several 3D unsteady-state fluid flow and heat transfer models considering various configurations were established based on geological data of Shacheng geothermal field, China. Next, nine working fluids were selected and the datasets of real thermophysical parameters were established for each working fluid. Finally, a critical comparison of various working fluids for U-tube DHE systems with different configurations was carried out and the suitability of each working fluid under same condition was evaluated. This paper provides some different insights into medium-low temperature geothermal resources development and gives a good guidance for improving the heat extraction performance of DHE geothermal systems.