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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

NUMERICAL ANALYSIS OF THE THERMAL CHARACTERISTICS OF A DOWNHOLE HEAT EXCHANGER GEOTHERMAL SYSTEM

Get access (open in a dialog) DOI: 10.1615/IHTC16.nee.023171
pages 7834-7841

Abstract

The downhole heat exchanger geothermal system is widely employed to develop geothermal resources for heating in residential and commercial buildings. To study the thermal characteristics of downhole heat exchanger system, a 3D unsteady state numerical model is presented to couple the fluid flow and thermal processes of downhole heat exchanger, wellbore and geothermal reservoir. Subsequently, the effects of the key factors, such as rock heat conductivity coefficient, reservoir porosity, subsurface water flow, on the heat extraction performance of downhole heat exchanger system are studied. In addition, the thermal performances of three downhole heat exchanger configurations, including spiral tube, multiple-tube with parallel connection and with serial connection, are compared. The simulation results depict that the effects of reservoir porosity on the downhole heat exchanger performance are minor and can be ignored. Higher subsurface water velocity and larger rock heat conductivity coefficient can both improve the downhole heat exchanger performance, but the former one has a more significant influence. Thus, compared with heat conduction, forced convection is dominated in the thermal process of geothermal reservoir. Besides, with the same tube number, the outlet temperature and thermal power of serial connection type downhole heat exchanger is higher than that of parallel connection type. Among the three configurations, the spiral tube downhole heat exchanger shows the best heat extraction performance. The key findings of this work are beneficial for the optimal design of downhole heat exchanger geothermal system.