The Theoretical And Experimental Study Of Fluid-Solid Heat Transfer For The Fracture Medium

In this paper, utilization of the Hot Dry Rock as the engineering background, fluid-solid heat transfer is studied in the process of heat extraction from the geothermal reservoir. Theoretical solution of water-rock heat transfer coefficient and experimental study are focused on.Firstly, the physical model, heat exchange between fluid and cylindrical rock with a single fracture, is built, and according to the energy conservation equation, the analytical solutions of water-rock heat transfer coefficient are derived in the fracture.Two kinds of analytical solutions are obtained through different methods. After analysis, some conclusions can be got:(a) the result from the 1D solution bigger than 2D solution;(b) at the condition of same aperture, the errors between two kinds of solutions increase with flow velocity;(c) at the condition of same flow velocity, the errors between two kinds of solutions also decrease with aperture.Microprocessor control electro-hydraulic servo rock triaxial tester TAW-2000 is developed to research heat exchange performance between water and rock in high temperature and high pressure. 50mm×100mm cylindrical rock samples are drilled, and then Brazilian test is applied to get rock samples with artificial fracture. Chosen four groups of rock sample temperature, three groups of confining pressure and ten groups of fluid flow, experiments are carried on to acquire 120 groups of data.By the analytical solutions, the heat transfer coefficients are calculated, and the results calculated by different solution and the reason are analyzed. The reason of error is the different calculation methods for inner surface temperature. Additionally, the experiment data are fitted to obtain two water-rock heat convection experimental correlations Nu=f(Re) and Nu=f(Re,Pr) for laminar flow(3.82<Re<27.84). At the conditions of different rock sample temperature, for Nu=f(Re,Pr), the sensitivity analyses of the parameters(Reynolds number and Prandtl number) are completed. The results( S*(Re)> S*(Pr)) demonstrate that Reynolds number plays a more important role in determining heat transfer performance than Prandtl number.