Heat transfer from hot dry rock to water flowing through a circular fracture

Surface averaged mass transfer coefficients on the wall of two circular disks between which spherical particles are randomly packed and the fluid flowed two-dimensionally from the inlet to the outlet were measured by means of the electrochemical method. The measured average mass transfer coefficients agreed with the calculated values, which were obtained by integrating the local mass transfer coefficient. Numerical simulation on heat transfer from the hot dry rock to flowing water in the circular fracture was performed by using the local heat transfer coefficients. The local heat transfer coefficients were obtained from the analogy between heat and mass transfers, in which the difference between the boundary condition for the heat transfer and that for the mass transfer in the laminar flow through the slit was taken into account. The result of the numerical simulation indicates that the forced convection between flowing water and the fracture surface has an important role in the heat transfer mechanism only in the early stage of heat extraction and the assumption that the temperature of the flowing water is equal to that of the fracture wall is, in practice, valid for the estimation of the water temperature at the production well. (C) 1999 CNR. Published by Elsevier Science Ltd.