Experiment of Heat Transfer in Downhole Heat Exchangers with a Promoter Pipe

Abstract

An experimental system of a downhole heat exchanger with a promoter pipe was established, and an aquifer simulated by a rectangular tank filled with glass beads (diameters between 3 -5 mm). A U-tube of copper was selected for modeling the downhole heat exchanger. Heat transfer performances of downhole heat exchangers were carried out for various cases by changing the promoter pipe length, the circulation flow rate, and the inlet temperature. The results indicate that the heat output for downhole heat exchangers with promoter pipe is higher than systems without promoter pipe due to natural convection. Promoter pipe length is an important parameter for heat output, and the larger the temperature difference between circulating water and aquifer, the higher the heat output. However, it does not necessarily follow a linear relation, so the design parameters should be selected carefully in order to obtain a more economical and feasible system.