Analytical and experimental studies of heat convection by water flow in rock fractures

Heat transfer analysis forms a major part of the studies of hot dry rock geothermal energy systems. Heat transfer from rock mass to working fluid is through convection in rock fractures. Analytical solutions of heat convection are based on the boundary layer concept and involve the principles of heat conduction and fluid dynamics. The convective heat transfer coefficient is found to be a function of the thermal conductivities of rock and water, flow velocity, dynamic and kinematic viscosities, specific heat, and geometry of the rock fracture. Measurements on rock-fluid heat transfer were collected during the flow experiments. The results showed that the convective heat transfer coefficient varies from 200 to 1400 W/m-° C, and is proportional to the flow velocity.