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CFD-modelling of natural convection in a groundwater-filled borehole heat exchanger

Gustafsson, A. -M.; Westerlund, L. and Hellström, Göran LU (2010) In Applied Thermal Engineering 30(6-7). p.683-691
Abstract
In design of ground-source energy systems the thermal performance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer... (More)
In design of ground-source energy systems the thermal performance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the borehole. The density gradient in the borehole is a result of the heat transfer rate and the mean temperature level in the borehole water. Therefore in calculations of the thermal resistance in groundwater-filled boreholes convective heat flow should be included and the actual injection heat transfer rate and mean borehole temperature should be considered. (C) 2009 Elsevier Ltd. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
model, Numerical, Buoyant flow, Natural convection, Borehole heat exchanger, U-pipe, Groundwater-filled borehole
in
Applied Thermal Engineering
volume
30
issue
6-7
pages
683 - 691
publisher
Elsevier
external identifiers
  • wos:000275976600019
  • scopus:76449084925
ISSN
1359-4311
DOI
10.1016/j.applthermaleng.2009.11.016
language
English
LU publication?
yes
id
ba0b1c5d-aa67-4a6b-8a70-3103547858f1 (old id 1587895)
date added to LUP
2010-04-22 13:35:35
date last changed
2018-05-29 09:21:35
@article{ba0b1c5d-aa67-4a6b-8a70-3103547858f1,
  abstract     = {In design of ground-source energy systems the thermal performance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the borehole. The density gradient in the borehole is a result of the heat transfer rate and the mean temperature level in the borehole water. Therefore in calculations of the thermal resistance in groundwater-filled boreholes convective heat flow should be included and the actual injection heat transfer rate and mean borehole temperature should be considered. (C) 2009 Elsevier Ltd. All rights reserved.},
  author       = {Gustafsson, A. -M. and Westerlund, L. and Hellström, Göran},
  issn         = {1359-4311},
  keyword      = {model,Numerical,Buoyant flow,Natural convection,Borehole heat exchanger,U-pipe,Groundwater-filled borehole},
  language     = {eng},
  number       = {6-7},
  pages        = {683--691},
  publisher    = {Elsevier},
  series       = {Applied Thermal Engineering},
  title        = {CFD-modelling of natural convection in a groundwater-filled borehole heat exchanger},
  url          = {http://dx.doi.org/10.1016/j.applthermaleng.2009.11.016},
  volume       = {30},
  year         = {2010},
}