To uilize the shallow geothermal energy, heat pumps are often coupled with borehole heat exchangers (BHE) for heating and cooling buildings. In cold regions, soil freezing around the BHE is a potential
problem which can seriously influence the underground soil temperature distribution, inlet and outlet fluid temperature of the BHE, and thus the efficiency of the whole GSHP system. The influence of the
freezing process on the overall system performance is investigated by comparing different BHE configuration with and without latent heat effect from the frozen groundwater. The coefficient of performance (COP) of the heat pump will alter when freezing process in taken into account and lead to various electricity consumption. Except for the efficiency aspect, the freezing behavior can also lead to the redistribution of pore pressure and fluid flow, and in some extreme cases can even result in frost damage to the BHEs. A fully coupled thermohydro-mechanical model is required for advanced system design and scenario analyses. Based on the framework of the Theory of Porous Media, a triphasic freezing model is derived and solved with the finite element method. Ice formation in the porous medium results from a coupled heat and mass transfer problem with phase transition and is accompanied by volume expansion. The model is able to capture various coupled physical phenomena through the freezing process including the latent heat effect, groundwater flow with porosity change and mechanical deformation. With this kind of THM freezing model, we are also able to solve different kinds of engineering problem, e.g. geotechnics, construction engineering and material engineering.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:34033 |
| Date | 20 May 2019 |
| Creators | Zheng, Tianyuan |
| Contributors | Kolditz, Olaf, Walther, Marc, Wang, Tiejun, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 10.1016/j.applthermaleng.2016.05.158, 10.1016/j.applthermaleng.2016.12.020 |
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