Comparison between typical numerical models for fluid flow and heat transfer through single rock fractures

Numerical models can explicitly characterize fluid flow and heat transfer processes in rock fractures including randomly distributed asperities and contacts and have been widely used to understand the behaviors of fluid flow and heat transfer in fractured rocks. The differences between three-dimensional and two-dimensional numerical models for single rock fractures were compared in terms of fluid flow and heat transfer behaviors and properties. Both the artificial fractures created by Brazilian tension method and the hypothetical fractures created by duplicating a fracture surface were considered. The results showed that hypothetical fractures and twodimensional models cannot capture the channeling flow and the non-uniform thermal fronts in artificial fractures, but two-dimensional models can predict the similar streamlines and thermal fronts as hypothetical fractures. The relationship between heat transfer coefficient and flow rate in a single rock fracture can be described by a logarithmic function, and the heat transfer coefficients of two-dimensional and three-dimensional models can be well correlated by an empirical function of fracture surface areas. The comparison between threedimensional and quasi-three-dimensional models of artificial fractures is also conducted. Both channeling flow and non-uniform thermal fronts from quasi-three-dimensional models became similar to the results of threedimensional models with increasing numbers of computational elements.