Study On Heat Transfer Characteristics Of Buried Underground Spiral Heat Exchanger

The ground source heat pump system is a new type of energy technology which uses the huge heat storage and storage capacity of the soil for heating and cooling.And the buried spiral heat exchanger is one of the new type of underground heat exchanger type,it not only has many advantages of traditional ground source heat pump system,but also alleviates the high initial investment,environmental pollution and other problems caused by drilling.In this paper,the underground heat transfer model of buried spiral heat exchanger is analyzed and summarized,and established: a single simulation model,and studied the factors such as the size parameters,back fill material,soil thermal property,inlet and outlet temperature and inlet flow rate.Finally,the heat transfer model composed of a single model is simulated and analyzed with ANSYS software,and the change and heat transfer characteristics of the soil temperature field around the spiral tube heat exchanger are analyzed,which provides a reference for future design and optimization analysis.In addition,this paper not only simulates the continuous storage(release)mode,but also simulates the operation of the intermittent operation mode.In particular,it is mentioned that the return pipe line passes from the helical center of the helical pipe,which alleviates the phenomenon of thermal short circuit in the back fill area to a certain extent.In the last chapter of this paper,the economics of several kinds of buried heat exchangers,which are common in life,are compared and analyzed.It is concluded that the double-U-type buried heat exchanger is a way of the most economy works.The final results of the analysis show that the four heat transfer zones exhibited by the spiral heat exchanger during the heat exchange process,include a small amount of heat transfer zone,backfill material heat short circuit area,an intermediate high heat exchange zone and a small amount of heat transfer zone at the bottom.The flow rate of helical pipe inlet is recommended: 0.3 ~ 0.5m/s,the spiral pipe pitch is recommended: 0.15 ~ 0.2m,pile radius is recommended to take: 0.75 m above,the inlet temperature is higher when the pitch and pile radius are large,on the contrary,the temperature can be slightly lower,which is the result of taking into account the back fill material area may be led to hot short circuit phenomenon,affecting the heat transfer characteristics at the same time.For the group analysis: the heat transfer characteristics of intermittent operation mode is better than the continuous,not only got large heat transfer,the distribution of soil temperature is relatively uniform.The same intermittent operation mode,the soil temperature and heat transfer of different running ratio and stop ratio are also different,the soil temperature distribution is relatively uniform in small running ratio and stop ratio,and the average temperature is higher.Therefore,it is necessary to analyze the relationship of the underground heat transfer characteristics of coil heat exchanger and the parameters affecting the heat transfer characteristics.