Experimental Study And Numerical Simulation On Thermal Properties Of Sand And Gravel Mixture

Soil thermal properties play a decisive role in the design of soil source heat pump heat exchanger.However,due to the composition of soil and the influence of Geology and hydrology,the study of soil thermal properties is relatively backward.The mixture of sand and gravel is a kind of backfill material used in the ground source heat pump system.Therefore,to study the thermal properties of actual conditions of sand gravel mixture,analyzed the variation of thermal properties in different geological and hydrological conditions of sand mixture,accurate simulation of soil source heat pump system has the important significance of the overall exchange process.In this paper,the sand mixture as the research object,based on the one-dimensional steady heat transfer theory is developed to measure large particles of gravel mixture under different consolidation pressure and different stone rate of the thermal conductivity instrument,and the sand mixture for thermal conductivity measurement;finally using ANSYS WORKBENCH finite element software for filling particles the shape,volume fraction of the filler was simulated as a supplement to test part of the uniform distribution case.Research findings:Test section: The coefficient of thermal conductivity of sand mixture increases with the increase of consolidation pressure.With the increase of sand content,due to the large size particles aggregate increases,the contact between particles is improved,resulting in thermal conductivity increases with the increase of sand content;the content of stone is mainly composed of two hours of thermal conductivity of sand particles and gravel control,with stone content increased the sand and gravel particle distance becomes shorter and the thermal conductivity of sand particles is less than gravel,leading to transfer more gravel by heat transfer,thermal conductivity increased gradually.The initial liquid water was added to make the formation of a thin layer of water film surface sand particles,resulting in particles formed between the surface contact,promote heat transfer between particles;with liquid water to join,increase the content of pore water and thermal conductivity of samples increases.Numerical simulation part: Based on the filling shape of cube and sphere of the representative volume unit of internal temperature and heat flux distribution simulation,get filling unit sphere shape temperature difference is greater than the unit cube filled the shape of the unit sphere filled with little influence on the boundary heat flux.With the increase of particle volume fraction,the temperature difference becomes smaller,and the flow direction of the unit is more obvious when the filler content increases.The thermal conductivity of the filler in the sphere filling content is less than 15%,the rapid growth of more than 15%,the growth trend of linear growth;thermal conductivity of cube filling particles slow down gradually with increase of filling content change trend.