The Analytical Solution of the Water-Rock Heat Transfer Coefficient and Sensitivity Analyses of Parameters

Abstract

Most previous works with respect to Enhanced Geothermal Systems (EGS) applied local thermal equilibrium method to study water-rock heat transfer. In order to use the local thermal non-equilibrium method that is close to actual condition, for the single fracture model, water-rock heat transfer coefficient analytical solutions are deduced using the energy balance. For the parameters related to the calculation, except the inner surface temperature, all the parameters can be obtained easily, but the inner surface temperature is necessary to the heat transfer coefficient. In one semi-circle section, by 2D heat conduction the heat fluxes from the inner surface and the inner surface temperature can be calculated, so the analytical solution of heat transfer coefficient is given. Then the measureable parameters from the reference are substituted into the solution and calculate heat transfer coefficient. Comparing the results with the reference, almost all the relative errors are less than 30%, and it shows that this method is receivable. At the conditions of four different outer surface temperatures, sensitivity analyses about two main parameters (flow velocity and aperture) are completed, and it indicates that the heat transfer coefficient is more sensitive to the flow velocity, but less to the aperture. Finally, for water-rock laminar heat convection model, the correlation equation is given, which is indicates the importance of Prandtl number to heat transfer.