Experiment And Numerical Study Of Seepage Heat Transfer In A Single Fracture Of Hot Dry Rock

In recent years,more and more attention has been paid to the quality of energy and environment,and it has been paid more and more attention to.The extraction of geothermal energy in dry hot rock is usually extracted by heat exchange between the fracture and the geothermal rock.Therefore,it is of great significance for dry hot rock engineering to study the mechanism of heat transfer in the fissure.In this paper,the 3D printing technology was used to prepare various kinds of rough fractures.The influence factors and the heat transfer mechanism of the seepage and heat transfer of the single fractured rock mass were studied by experiments,numerical simulation and evaluation.The seepage and heat transfer experiments were carried out to analyze the flow and heat transfer characteristics of the rough surface;the numerical simulation is carried out based on the numerical simulation software of plate laminar heat transfer theory;using quantitative global sensitivity analysis,the main conclusions are as follows:First of all,22 block flow direction and vertical flow direction of rough fracture seepage of rock samples were prepared by 3D printing method based on Barton curve standard rough.On this basis,seepage experiments were carried out,the experimental results show that with the increase of roughness of the fracture flow and the equivalent hydraulic aperture decreased;in reducing seepage flow,vertical flow direction the roughness of the smallest effect,the largest effect two-dimensional rough fracture,the fracture surface with high roughness in the two-dimensional fracture surface is larger effect than the fracture surface with low roughness,the roughness of seepage direction is larger effect than that of vertical seepage direction.Secondly,22 block flow direction and vertical flow direction of rough fracture seepage of rock samples were prepared based on Barton curve standard rough.,the seepage heat transfer experiment was carried out,the experimental results show that the convection of various rough fracture rock heat transfer coefficient with the increase of flow rate increases,with the crack surface temperature increases the convective heat transfer coefficient gradually increase;vertical flow direction roughness to improve the convective heat transfer coefficient function minimum,two-dimensional rough fracture to improve the convective heat transfer coefficient effect is relatively large;the flow direction and vertical direction of rough fracture seepage heat transfer mechanism is similar,mainly affected by heat transfer area and local turbulence,the heat transfer mechanism of two-dimensional rough fracture increases the influence of seepage path;the curves of Nu,Re and Pr were fitted to 22 kinds of rough fracture surfaces and the corresponding characteristic number equation is given.Again,theoretical comparison is made through numerical simulation of seepage and heat transfer of single fractured rock mass,the results of numerical simulation and experimental results of straight fractured,seepage direction different roughness fracture surface and vertical seepage direction different roughness fracture surface rock samples are small;the contrast error of the two dimensional rough rock specimen is larger,not suitable for approximation calculation of laminar flow heat transfer theory.Finally,the influence of the experimental variables on the heat transfer experiment is evaluated by the global sensitivity evaluation method.In all kinds of rough fracture seepage and heat transfer experiment,rock temperature plays an important role in the improvement of outlet temperature;the effect of roughness on the fracture surface in the seepage direction is larger than that in the vertical seepage direction;in the experiment of two-dimensional rough fracture surface,the fracture surface roughness of No.1 is larger than that of No.2,but No.1 fracture surface flow heat transfer effect is lower than 2,the results of numerical simulation and experimental results are close to those of the straight and one-dimensional cracks;the results of numerical simulation of two-dimensional fracture surface and seepage heat transfer experiment are quite different.