Study On The Influence Of The Initial Soil Temperature And Groundwater Seepage On The Heat Exchanger With Several Supply Pipes And One Return Pipe

Nowadays,the demands for energy of the world has been increasing,and the following environmental problems cannot be ignored.The contradiction which between supply and demand and environmental destruction have become problems that need to be resolved urgently.The vertical buried pipe ground source heat pump system using geothermal energy is beginning to be widely used due to its unbelieveable strengths.And the strengths of the vertical buried pipe ground source heat pump system are extremely prominent,it has become the most widely used heat pump system,especially in cold regions.The core component of the ground source heat pump system is the underground heat exchanger,which plays an important role in the operation of the entire system.To improve the efficiency of the heat exchanger and to reduce tthe negative impact of the "thermal short circuit" between the water supply and return pipes,many scholars have proposed many new types of buried heat exchangers.At present,all the research of new borehole heat exchangers have been based on numerical simulation because of many facters’ restriction.In order to make the results of simulation closer to the real situations,scholars can design or optimize the borehole heat exchanger based on the conclusions,and make contributions to the actual project.The setting of conditions in the simulation software needs to be closer to the local real situations.In the Loess Plateau,as the underground depth increases,the component of soil is not homogeneous,so the physical properties are different.There may be flowing groundwater in different soil layers due to different water content.And according to the thermal response test and experiment of the local rock and soil,the initial temperature of the soil at different depths is not the same.Based on the actual soil environment in the Loess Plateau,this research studies the effect of groundwater seepage on the heat transfer of a new type of buried pipe heat exchanger——Several Supply Pipes and One Return Pipe.Taking these actual factors into consideration in the simulation process,The modeling software Design Molder was used to create a three-dimensional heat-permeable coupled heat transfer numerical model for heat exchanger with a quantity of 2 to 5 water supply pipes and the surrounding rock and soil.And its physical model is meshed by Meshing.The numerical model’s results in this paper appears accurate with the experimental data in literature.The ANSYS FLUENT software was used to compare and study the effects on the transfer performance of the initial soil temperature at a fixed value and the initial temperature which changes in the buried depth under the layered soil.Taking the temperature cloud map and the thermal influence radius as indicators,it can be showed that under different initial temperature,the outlet’s temperature of the buried pipe is in less different,but the difference in total heat exchange cannot be ignored.Therefore,in the simulation,ignoring the change of the initial temperature will cause the calculated value of heat exchange to be higher.Through the analysis of the outlet temperature and unit axial heat transfer results of one more groundwater flow direction in different groundwater flow directions,It shows that the seepage direction is different,and the same branch pipe in the same number of water supply pipes is affected and changed.Therefore,there is always an optimal seepage direction for each type of several supply pipes and one-return pipe heat exchangers,so that the total heat exchange between it and the soil is the largest,and the heat exchange efficiency is the highest.According to the simulation of heat exchange with several supply pipes and one return pipe.under intermittent operation conditions,constant load conditions,and high-low variable load conditions.It’s concluded that no matter what conditions,there will be a minimum in the process of water temperature change in the buried pipe.The heat recirculation phenomenon will appear downward in this minimum value area.The cylindrical water trap required for the borehole heat exchanger involved in this article has not shown a good product in the actual project,and it needs to be further studied and used in experiments.The theory and practice are combined to promote this New type buried heat exchanger.