Lattice-boltzmann Method Simulation Of Liquid-gas Phase Change In Wet Rock Soil In The Process Of Absorption Of Heat

Geothermal energy is a clean and renewable energy source,and Ground Source Heat Pump(GSHP)technology is widely used to extract shallow geothermal energy.The soil-source heat pump system is a shallow geothermal energy utilization system that extracts the energy stored in the rock and soil by using an underground pipe heat exchanger.As a place for heat absorption and heat removal,it is of great significance to study the coupling mechanism of heat and moisture in the process of heat absorption and release in the rock and soil layers for the efficient utilization of the soil-source heat pump system.In this paper,the lattice Boltzmann method is used as a numerical simulation method to study the gas-liquid phase change and flow mechanism in the the phase thinning zone and porous media during the heat absorption process.Firstly,the theoretical basis of LBM is introduced in detail.Some common boundary conditions in LBM and their application situation are introduced.The lattice Boltzmann method for phase transition is described in detail.Secondly,the flow and gas-liquid phase change mechanism in the thin zone of rock-soil in the process of heat absorption is studied.The effects of different degree of superheat and fluid wettability on the flow field and temperature field in the phase thinning region are studied.The results show that the wall superheat is inversely proportional to the time of bubble formation.The higher the core temperature is,the less time it takes for the gas phase to break away from the wall,and the larger the bubble diameter is.The contact angle is inversely proportional to the time of bubble leaving the wall.Hydrophilicity and hydrophobicity determines the degree of difficulty in forming gas film.The greater the contact angle is,the better the heat transfer effect in the temperature field is.Finally,the coupling mechanism of heat and moisture in porous media of rock and soil during heat absorption is studied.The effects of soil porosity,wall temperature and fluid wettability on the flow and temperature fields in porous media are studied.The results show that the greater the porosity of porous media,the smaller the hindrance to the occurrence of the initial phase transition and the flow of the gas phase,the phase transition between gas and liquid,and the heat transfer is,and the greater the average velocity and the average heat flow density when the steady state is reached.The higher the wall superheat is,the more intense the initial gas-liquid phase change process is,the larger the initial average velocity is in the calculation domain,and the greater the heat flux value is in the rock and soil layer in the stable state.The hydrophilic and hydrophobic interface has a great relationship with the wall velocity of GSHP.The smaller the contact angle is,meaning the stronger the hydrophilicity is,which makes it easier to form an air film.Therefore,the weaker its ability to pass through tiny pores is,the closer the diffusion distance is when it reaches a stable state,and the heat transfer deteriorates for the solid wallliquid phase.