Analysis Of Heat Transfer Characteristics Of Buried Tube Heat Exchanger Under Seepage Condition Based On Adaptive Load

As a high-efficiency and low-pollution renewable energy technology,ground source heat pump(GSHP)is widely used in the current situation of increasingly energy shortage.The study of the heat transfer characteristics of the borehole heat exchanger is the key to the study of the ground source heat pump system,and it is necessary to consider the groundwater seepage factor in the study of the heat transfer characteristics of the borehole heat exchanger.The research on the heat transfer characteristics of the borehole heat exchanger under the condition of groundwater seepage is particularly important.The currently widely used calculation method usually assume the total heat transfer load equally distributed to each buried pipes when analyzing the heat transfer of borehole heat exchangers under seepage conditions.In fact,the long-term operation of the multi-borehole heat exchanger will cause nonuniform soil temperature distribution,so that the actual heat transfer load of buried pipes at different locations is no longer the same.For this reason,this thesis considers the fact that the thermal load of each buried pipe is no longer the same in real time in different parts of the pipe layout area.For the cluster borehole heat exchanger under the condition of groundwater seepage,the analysis and calculation methods of heat transfer simulation and the different methods are compared and analyzed.In-depth research on the heat transfer characteristics of the borehole heat exchanger was carried out by various influencing factors.In this thesis,the method of load adaptive distribution is used for simulation calculation,and the heat transfer characteristics of the borehole heat exchanger under the condition of groundwater seepage are analyzed.This calculation method of load adaptive distribution first assumes that each buried pipe in the underground buried pipe area is The inlet water temperature is equal,and the real-time heat exchange load of each buried pipe is determined by the heat exchange conditions at that time.The sum of the heat exchange loads required by all the buried pipes is the total heat exchange load of the borehole heat exchanger.This method makes up for the deficiency of the current load sharing method assuming that each buried pipe bears the same heat transfer load,and is more suitable for the actual operation of the buried pipe heat exchanger.The results obtained by the calculation method of load adaptive distribution show that,the difference increases with the increase of the operating time and the scale of the heat exchanger;the load variation of each buried pipe is the negative feedback of the variation of the surrounding soil temperature.Therefore,the soil temperature field in the buried pipe area will not be seriously unevenly distributed.The inhomogeneity of soil temperature field obtained by the load-sharing method is significantly higher than that obtained by the adaptive load method.Based on this,the conclusion that the accumulation of cold or heat in the downstream area of seepage is more serious than that in the upstream area probably be quite different from the actual situation.The effects of the seasonal load ratio on the operation of the borehole heat exchanger was studied,and the effect of the ground source heat pump system on the heat transfer characteristics of the borehole heat exchanger was also calculated in the areas with different groundwater seepage rates and different groundwater seepage directions.The effects of seasonal load ratio in summer and winter,groundwater seepage velocity and seepage direction on the operation of the underground borehole heat exchanger were are studied.The calculation results show that the larger the seasonal load ratio,the higher the overall temperature of the soil,and the relatively high underground temperature in the downstream area in summer,which leads to the reduction of the heat release of each buried pipe in this area,and the decrease of the heat release of each buried pipe will slow down the area.temperature rise in this area.That is,there is a negative feedback effect between the underground temperature and the heat exchange of the buried pipe,so that the soil temperature field has a selfregulating effect of spontaneously suppressing excessive imbalance.Therefore,the soil temperature field distribution in the entire buried pipe area is relatively uniform,and there will be no serious cold or heat accumulation.The borehole heat exchanger is suitable for operation in areas with high groundwater seepage velocity.At the same time,in areas with different seepage directions,the heat transfer efficiency of the borehole heat exchanger is also different.The area with the seepage direction angle of 45° is most favorable for the operation of the ground source heat pump system.Based on the selected heat transfer model and calculation method,a software with friendly human-computer interface is developed to simulate the heat transfer of borehole heat exchanger under the condition of groundwater seepage.The software is easy to operate,and it can perform simulation with or without seepage.It is beneficial for researchers to study the heat transfer characteristics of the borehole heat exchanger,and also enables engineers to conveniently design the borehole heat exchanger.