Programming Research On Heat Transfer Performance Of Buried Heat Exchangers Coupling Inside And Outside Of Tube And Phase Change

With the rapid development of community economy,energy crisis and environmental pollution problems have posed a serious threat to human needs and health.In order to respond to energy conservation and environmental protection policies,it is urgent to develop energy-saving technologies and search for new energy resources.As a renewable energy technology,ground source heat pump(GSHP)technology plays an important role in reducing building energy consumption and pollution.The problem of heat exchanger between ground source heat pump and shallow soil has become the focus of research in order to promote the development of ground source heat pump technology.Based on the idea finite element and combining the theory of porous media and fluid dynamics theory,a heat and mass transfer model is established by using Fortran language tool for buried tube heat exchangeraiming at GSHP,which couples turbulent flow field in the tube with groundwater seepage in the surrounding soil.In this paper,U-type buried tube,U is equivalent to U-type Square tube.A model of soil cool storage considering solid-liquid phase transition process and a 3D dynamic numerical calculation program is compiled.Finally,this paper analyzes the influence of different factors on the heat transfer performance of the buried tube heat exchanger.In the process of applying ground heat exchangers to soil storage and heating in cold regions,groundwater may be frozen in the soil around the ground heat exchangers.An evaluation indexes of the linear heat flux is derived to describe the heat transfer performance of the buried tube heat exchanger in this paper.The influence of solid-liquid phase change on soil storage was compared and analyzed.Based on the computation of turbulent tube,this paper analyzes the influence of the different seepage velocity,different buried tube entrance velocity,different buried tube entrance temperature,different backfill materials and different buried pipe on heat exchanger performance.The results are as follows:(1)The soil seepage is favorable to the heat transfer of the buried tube,the greater the seepage velocity,the stronger the heat transfer performance of the buried pipe tube heat exchanger.And the linear heat flux increase averagely by 0.06% when the seepage velocity increases by 10m/a;(2)With the increase of inlet velocity,the outlet temperature increases,the linear heat flux increases significantly.And there is an optimal inlet velocity;(3)Under the condition of constant flow rate,with the increase of the inlet water temperature,the temperature difference between the inlet and outlet of the buried tube increases and the linear heat flux will increase;(4)The higher the thermal conductivity of backfill material,the better effect of heat transfer.And the thermal conductivity of backfill materials should be close to the thermal conductivity of the soil.The corresponding heat flux increases averagely by 18.74 W/m,an increase of 15.3% when thermal conductivity increases by one unit;(5)High heat conduction performance of HDPE tube,PE tube and PB tube is helpful to improve the buried tube heat exchanger performance.(6)Liquid phase change process of soil cold storage improves buried tube heat transfer performance of the heat exchanger.There will be some fluctuations of outlet temperature when the phase transition phenomenon appearing.The relative difference of the linear heat flux between phase change process and no phase change process is 5.4%.