Laboratory Experimental Investigation of Heat Transport In

9 Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays, in 10 relation to its potential for development in the society worldwide. Most of its applications have 11 already been investigated, such as: heating and cooling of private and public buildings, roads defrost, 12 cooling of industrial processes, food drying systems or desalination. 13 Geothermal power development is a long, risky and expensive process. It basically consists of 14 successive development stages aimed at locating the resources (exploration), confirming the power 15 generating capacity of the reservoir (confirmation) and building the power plant and associated 16 structures (site development). Different factors intervene in influencing the length, difficulty and 17 materials required for these phases thereby affecting their cost. 18 One of the major limitations related to the installation of low enthalpy geothermal power plants 19 regards the initial development steps which are risky and the upfront capital costs that are huge. 20 Most of the total cost of geothermal power is related to the reimbursement of invested capital and 21 associated returns. 22 In order to increase the optimal efficiency of installations which use groundwater as geothermal 23 resource, flow and heat transport dynamics in aquifers need to be well characterized. Especially in 24 fractured rock aquifers these processes represent critical elements that are not well known. Therefore 25 there is a tendency to oversize geothermal plants. 26 In literature there are very few studies on heat transport especially in fractured media. 27 This study is aimed to deepen the understanding of this topic through heat transport experiments in 28 fractured network and their interpretation. 29 Heat transfer tests have been carried out on the experimental apparatus previously employed to 30 perform flow and tracer transport experiments, which has been modified in order to analyze heat 31 transport dynamics in a network of fractures. In order to model the obtained thermal breakthrough 32 2 curves, the Explicit Network Model (ENM) has been used, which is based on an adaptation of a 33 Tang’s solution for the transport of the solutes in a semi-infinite single fracture embedded in a porous 34 matrix. 35 Parameter estimation, time moment analysis, tailing character and other dimensionless parameters 36 have permitted to better understand the dynamics of heat transport and the efficiency of heat exchange 37 between the fractures and matrix. The results have been compared with the previous experimental 38 studies on solute transport. 39