ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

A comprehensive transient heat transfer simulation of U-tube borehole heat exchanger considering porous media and subterranean water seepage

Mehdi Mehrpooya, Farzad Ghafoorian, Seyed Parsa Mohammadi Afzal, Seyed Reza Mirmotahari, and Mohammad Reza Ganjali

School of Energy Engineering and Sustainable Resources, College of Interdisciplinary Science and Technology, University of Tehran, Tehran, Iran

E-mail: mehrpoya@ut.ac.ir

Received: 17 February 2024  Accepted: 22 March 2024

Abstract:

The present study involves a numerical simulation of a borehole heat exchanger (BHE) configuration that utilizes computational fluid dynamics (CFD) methodology. The BHE comprises a U-shaped pipe that facilitates the thermal exchange between water entering from one end and exiting from the opposite end. These heat exchangers are employed for both heating and cooling applications. This study concerns a system that employs water as its working fluid. The water enters a pipe at a higher temperature than that of the surrounding soil and subsequently exits with a lower temperature. The borehole wall temperature is examined in order to investigate the effects of inlet mass flow rate, backfill porosity, the presence of subterranean water, and its seepage velocity on the convection and conduction heat transfer, as well as on the system's performance. The results indicate that an increase in mass flow rate improves convection heat transfer. A porosity of 0.6 is deemed suitable under conditions of the absence of subterranean water, while a porosity of 0.2 is considered appropriate for backfill saturation and the presence of subterranean water. Also, an increase in subterranean water velocity seepage increases convection heat transfer, albeit at the expense of a decrease in system performance.

Keywords: U-tube borehole heat exchanger; Backfill porosity; Subterranean water seepage; Convection heat transfer; Conduction heat transfer

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-024-03443-0

Chemical Papers 78 (11) 6315–6329 (2024)