Study On Influence Of Soil Porosity On Heat Transfer Of Vertical Buried Tube Heat Exchanger

Ground-source heat pump is a kind of shallow geothermal energy application form in the background of energy crisis,environmental pollution and ecological damage.It has the characteristics of energy saving and environmental protection.It is the key support in China’s 13 th Five-Year Plan.One of the forms of development of renewable energy applications.Through the review of the status quo of ground source heat pump research at home and abroad,the ground source heat pump system in the form of vertical buried pipe is widely used.The vertical heat pipe heat exchanger and soil heat conduction are the key points and difficulties in the research of ground source heat pump system.Soil is a typical porous medium,and its heat and mass transfer is a complicated process.However,some physical parameters of soil are difficult to obtain in actual engineering.Soil physical parameters have certain heat transfer to vertical heat exchanger.The influence,therefore,limits the in-depth study of heat transfer between the vertical buried heat exchanger and the soil.In this paper,we firstly design and build a test bench,screen three different particle sizes of soil and change the soil moisture content to change the soil porosity,to study the change of different particle sizes and different water content and change the different soil porosity to the vertical buried pipe.The heat transfer effect of the heat exchanger;then the physical model is established by the parameters of the test bench,the soil parameters are tested as the boundary conditions,the experiment is simulated and compared with the Fluent software,and the numerical simulation model is established;finally,based on the established model,The simulation study on the effects of different soil porosity on the heat transfer of vertical borehole heat exchangers.Experimental results show:(1)The soil particle size is numbered from small to large.The soil particle size is between 0.25 and 0.5 mm for soil 1.The soil particle size is between 0.25 and 0.5 mm for soil 2.The soil particle size is between 0.25 and 0.5.Between mm is soil 3.The soil moisture content is the same,and different soil particle sizes are changed to obtain different soil porosity.Experiments show that the average thermal conductivity of soil decreases with increasing porosity.From soil 1 to soil 2,the porosity increased by 10.3%,the average thermal conductivity decreased by 2.4%;the average heat transfer decreased by 3.0%;from soil 2 to soil 3,the porosity increased by 8.6%,and the average thermal conductivity decreased by 1.9%.The average heat exchange decreased by 2.5%.The analysis shows that for this experiment,the change of soil porosity has little effect on the average thermal conductivity of soil,and the change of soil porosity has little effect on the heat transfer.(2)The soil particle size is the same,and the soil moisture content is changed by changing the soil water content.Experiments show that the average soil thermal conductivity increases with the increase of porosity,and the average heat exchange rate increases with the porosity.Increase and rise.Soil 3 increased by 3.8% from 5% moisture content to 10% moisture content,average thermal conductivity increased by 9.8%;average heat transfer increased by 7.2%;soil 3 from moisture content of 10% to moisture content of 20% porosity The increase was 3.9% and the average thermal conductivity increased by 8.3%.The average heat exchange rate increased by 6.8%.The analysis shows that for this experiment,the change of soil porosity has a great influence on the average thermal conductivity of soil;the change of soil porosity also has a great influence on the heat exchange.(3)It can be obtained through two sets of experimental comparisons: the effect of soil porosity changed by different soil water content on the heat transfer of vertical borehole heat exchanger is greater than that of soil porosity changed by vertical soil.The impact of the device.The simulation results show that:(1)By comparing the experimental conditions and experimental results of Fluent simulation,the difference between the two is very small.It can be considered that the simulation and the experiment can correspond well.The numerical simulation model established by the experimental physical model is correct.(2)Keeping other soil physical properties unchanged,only changing the soil porosity,which is equivalent to changing the soil particle size.As the porosity increases,the heat exchange rate decreases,and the soil porosity increases from 0.2 to 0.5.The amount was only reduced by 4.3%,indicating that only the change of soil porosity under different soil particle size has little effect on heat exchange.(3)By experimenting with different soil porosity experiments changed by changing different water contents,the simulated parameters were simulated,and the soil porosity increased by 9.2% from 0.441 to 0.482,and the heat exchange rate increased by 20%.The different soil porosity underneath has a greater impact on the heat transfer.