Investigations into thermal resistance of tunnel lining heat exchangers

Geothermal energy is a promising and sustainable source that can reduce current dependence on conventional fuels for thermal energy production. To exploit this source of energy thermo-active geostructures such as tunnel lining heat exchangers are being investigated theoretically as well as experimentally. These geostructures are composed of concrete panels embedded with reinforcement cages fitted with absorber pipes. Several engineering projects in China, Finland and Italy have deployed such heat exchangers in tunnels. To achieve efficient energy production, characterisation of these systems require realistic models of the substructure heat exchanger. Therefore investigations into thermal resistance of the heat exchanger is vital. The present study is concerned with quantifying the thermal resistance of tunnel lining heat exchangers where the thermal boundary surfaces are applied at surfaces representing the adjacent ground and the exposed concrete, in addition to the pipe surface. Steady state temperature distribution in a two dimensional cross section of a tunnel lining heat exchanger is investigated using the boundary collocation least squares method. Design parameters including pipe and tunnel lining specifications are used as model inputs.