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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

HEAT STORAGE ANALYSIS OF ENERGY PILES WITH SPIRAL-TUBE HEAT EXCHANGER BASED ON A PRACTICAL AXISYMMETRIC MODEL

Get access (open in a dialog) DOI: 10.1615/IHTC16.nee.023433
pages 7858-7865

Abstract

Energy pile is an attractive and cost-effective solution for ground-coupled heat pump systems to partly take the place of borehole ground heat exchangers. A practical axisymmetric model has been established for an energy pile with spiral-tube heat exchanger and is solved by using the finite element method. The coupled boundary conditions of fluid temperature and heat flux between fluid and pipe are appended to this model. The simulation for the model are in good agreement with the test data. The comparison between the model and 3-D model indicates that the simulation of 2-D model is consistent with that of 3-D model when the length ratio of spiral tube to vertical tube is >4.1. The agreement decreases as the length ratio of spiral tube to vertical tube decrease from 4.1 to 1.4, but all relative errors are <5% when the running time is >5 hours. Then the heat storage characteristics of an energy pile are investigated in consideration of the thermal diffusion coefficient of grout, the aspect ratio of energy pile, the relative pitch of spiral-tube and the curvature of coil pipes. A quasi-steady state of heat storage occurs when Fo?10 due to constant inlet fluid temperature.