Abstract
As fluid passes through the fracture of an enhanced geothermal system, the flow direction exhibits distinct angular relationships with the geometric profile of the rough fracture. This will inevitably affect the heat transfer characteristics in the fracture. Therefore, we established a hydro-thermal coupling model to study the influence of the fluid flow direction on the heat transfer characteristics of granite single fractures and the accuracy of the numerical model was verified by experiments. Results demonstrate a strong correlation between the distribution of the local heat transfer coefficient and the fracture morphology. A change in the flow direction is likely to alter the transfer coefficient value and does not affect the distribution characteristics along the flow path. Increasing injection flow rate has an enhanced effect. Although the heat transfer capacity in the fractured increases with the flow rate, a sharp decline in the heat extraction rate and the total heat transfer coefficient is also observed. Furthermore, the model with the smooth fracture surface in the flow direction exhibits a higher heat transfer capacity compared to that of the fracture model with varying roughness. This is attributed to the presence of fluid deflection and dominant channels.
Highlights
Geothermal energy is a clean and environmentally friendly renewable energy source with a wide distribution range, large reserves, and long duration [1,2,3]
Chen [33] established a geothermal reservoir model with a rough fracture surface based on small-scale research results, revealing the constant heat transfer coefficient (HTC) recommended in previous studies to underestimate the final outlet fluid temperature in the case of rough fractures
Sci. 2021, 11, 751 case of rough fractures. These studies demonstrate that research on the influence of3forfa2c1ture morphology on the fluid flow and heat transfer process at the experimental scale can be applied to the actual site model [28,34]
Summary
Geothermal energy is a clean and environmentally friendly renewable energy source with a wide distribution range, large reserves, and long duration [1,2,3]. Zhang [24] established a three-dimensional numerical model based on threedimensional laser scanning to evaluate the effects of rock temperature, water flow velocity, roughness, and fracture aperture on the heat transfer coefficient. Chen [33] established a geothermal reservoir model with a rough fracture surface based on small-scale research results, revealing the constant heat transfer coefficient (HTC) recommended in previous studies to underestimate the final outlet fluid temperature in the case of rough fractures. Sci. 2021, 11, 751 case of rough fractures These studies demonstrate that research on the influence of3forfa2c1ture morphology on the fluid flow and heat transfer process at the experimental scale can be applied to the actual site model [28,34]. The enthalpy of water can be determined by numerical simulations of the inlet and outlet temperature and pressure
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