Simulation of the thermal borehole resistance in groundwater filled borehole heat exchanger using CFD technique
2010 (English)In: International Journal of Energy and Environment, ISSN 2076-2895, E-ISSN 2076-2909, Vol. 1, no 3, 399-410 p.Article in journal (Refereed) Published
The thermal borehole resistance in a groundwater-filled borehole heat exchanger (BHE) is affected of both conductive and convective heat transfer through the borehole water. To calculate this heat transport, different models are required compared to calculation of only conductive heat transfer in a back-filled BHE. In this paper some modelling approximations for groundwater-filled, single U-pipe BHEs were investigated using a 3D CFD model. The purpose is to find approximations that enable to construct a fast, simple model including the convective heat transfer that may be used in thermal response test analyses and BHE design programs. Both total heat transfer calculations (including convective and conductive heat transport) and only conductive heat transfer calculations were performed for comparison purposes. The approximations that are investigated are the choice of boundary condition at the U-pipe wall and using a single pipe in the middle of the borehole instead of the U-pipe. For the total heat transfer case, it is shown that the choice of boundary condition hardly affects the calculated borehole thermal resistance. For the only conductive heat transfer case, the choice of boundary condition at the pipe wall gives large differences in the result. It is also shown that using an annulus model (single pipe in the middle of the borehole) results in similar heat transfer as the U-pipe model provided that the equivalent radius is chosen appropriately. This approximation can radically decrease the number of calculation cells needed.
Place, publisher, year, edition, pages
2010. Vol. 1, no 3, 399-410 p.
Research subject Urban Water Engineering; Energy Engineering
IdentifiersURN: urn:nbn:se:ltu:diva-16178Local ID: fc622440-6ca8-11df-ab16-000ea68e967bOAI: oai:DiVA.org:ltu-16178DiVA: diva2:989154
Godkänd; 2010; 20100531 (amg)2016-09-292016-09-29Bibliographically approved