Доступ предоставлен для: Guest

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 INVESTIGATION ON THE HEAT EXTRACTION PERFORMANCE OF COAXIAL BOREHOLE HEAT EXCHANGER GEOTHERMAL SYSTEM

Get access (open in a dialog) DOI: 10.1615/IHTC16.nee.023177
pages 7625-7632

Аннотация

The coaxial borehole heat exchanger geothermal system is expected to be used for exploiting deep geothermal resources because of a larger heat transfer area than traditional U-tube borehole heat exchanger. To reduce heat dissipation of working fluid in central pipe, a multi-layer insulated central pipe is employed in this paper. However, to the best of our knowledge, most previous heat transfer models considered the central tube as a single-layer structure, which is inconsistent with the actual conditions. Thus, we present an unsteady-state heat transfer model considering the complete structure of central tube to investigate its heat extraction performance. The finite difference method is employed to solve the mathematical model, and the model is validated with field data. Subsequently, the effects of the key factors, including inlet temperature, mass flow, insulation section length of central tube, wellbore diameter, on the performance are studied. The simulation results depict that the outlet temperature decreases greatly at the initial stage, but then remains relatively stable. There is a critical value for the flow rate to obtain higher thermal power with appropriate pressure drop. The lower inlet temperature can enhance heat transfer. In addition, the insulated central pipe can significantly reduce heat dissipation. There is an optimum insulation section length for central tube in terms of cost and heat insulation effect, which is about 3500m. The main findings of this work can offer guidance for the optimal design of geothermal system.