Influence of normal stress‐induced three‐dimensional rough fracture aperture heterogeneity on nonlinear seepage‐heat transfer coupling processes.

A clear understanding of the dependence of the heat transfer process on the flow field in three‐dimensional (3D) rough fractures is crucial for many underground projects. In this study, 3D rough rock fractures with heterogeneous apertures and mechanical effects are established. Navier‐Stokes flow and local heat balance theory are used to simulate the seepage‐heat transfer coupling process. Five normal stresses and five flow velocities are set to quantify the influence of aperture variability on the flow field and heat transfer behavior of the fractures. The results show that the change in fracture aperture caused by normal stress is the direct cause of the nonlinear distribution of the flow field and temperature fluctuation. A quantitative parameter of temperature fluctuation degree in the fracture is proposed, which decreases exponentially with increasing fracture aperture and increases with greater flow velocity. An empirical model is established to describe the relationship between the heat transfer coefficient and the ratio of hydraulic aperture to mechanical aperture. The correctness of the model is verified by published seepage‐heat transfer coupling test results. The model is extended to establish the relationship between the heat transfer coefficient and the volume fraction of eddy. It is confirmed that the heat transfer coefficient increases with the augmentation of nonlinear flow, and the reason why the results of evaluating the heat transfer coefficient by roughness alone in related experiments are inconsistent is revealed. The results enhance the understanding of convective heat transfer characteristics in 3D rough rock fractures. [ABSTRACT FROM AUTHOR]