Volume 62

A Study on Thermal Performance of an Increasing-Pressure Endothermic Power Cycle with a Geothermal-well Downhole Heat Exchanger Zheng Wang, Tao Liu, Xinli Lu, Wei Zhang, Jiali Liu, Lei Chen

Abstract

In this study, thermal performance of an increasing-pressure endothermic power cycle (IPEPC) has been numerically investigated. In the IPEPC, a downhole heat exchanger (DHE) is used to replace a traditional evaporator on the ground. Matching relationships among four key parameters (DHE inlet pressure, DHE length, geothermal water temperature, and geothermal water mass flow rate) and the working fluid mass flow rate are quantitatively analyzed. The research results indicate that, when the DHE inlet pressure is 3.7MPa and the geothermal water temperature is 95°C, the optimal working fluid mass flow rate is 9 kg/s, corresponding to a maximum net power output of 45.11kW. When the geothermal water temperature is 130°C, the optimal working fluid mass flow rate is 9.5 kg/s, with a maximum net power output of 111.7kW. As the geothermal water mass flow rate increases, the optimal working fluid mass flow rate increases synchronously, and the net power output under this matched operating condition also shows an upward trend. Under the condition that the working fluid mass flow rate is low (ranging from 3 to 6 kg/s), using a shorter DHE length results in a better thermal performance. When the working fluid mass flow rate is high (ranging from 6 to 12 kg/s), using a longer DHE is an effective way to increase the net power output. The findings of this study provide theoretical guidance for IPEPC system optimization and engineering design.

Keywords increasing-pressure endothermic process geothermal power cycle, downhole heat exchanger, thermal performance analyses