Research On Flow And Heat Transfer Characteristics Of Buried Concentric Tube Heat Exchanger In Severe Cold Area

The demand for heating in the severe cold area is large,and the application of the geothermal heat pump system in the region has significant economic,social and environmental benefits,the key to the technology of the geothermal heat pump system lies in the accurate grasp of the heat transfer characteristics of the underground geotechnical and heat exchanger,however,the previous related research focused on the U-type buried heat exchanger,and lacked the theoretical and experimental research on the buried concentric tube heat exchanger.Due to the complexity of deep-hole heat transfer in cold regions,the relevant theories and applications is even rarer,and there is no universally accepted specification for heat transfer model research.Thus,in this paper,a semi empirical design model,two-dimensional analytical model and two-dimensional numerical model suitable for severe cold regions are set up for buried concentric tube heat exchanger,with a view to guiding the relevant engineering practice in some extent.The paper is based on the ideological and theoretical analysis and experimental testing of combining gradually.The research methods of this paper can be divided into the following aspects: designed and set up a test bed after the field survey of geological conditions,preparation of casing heat exchanger flow resistance calculator,and use of international advanced thermal test equipment for experimental testing;the influencing factors of the single heat transfer are analyzed based on the control variable method,and the influence of circulating liquid flow rate and heat exchanger water supply temperature is discussed emphatically.Demonstrated the rationality of the various models that simplify the assumptions,on the basis of this,a semi empirical design model,two-dimensional analytical model and two-dimensional numerical model suitable for severe cold regions are set up for buried concentric tube heat exchanger;the experimental data were used to verify the heat transfer model;the numerical simulation of coupled heat transfer is carried out by using the control volume method to obtain the coupled temperature field distribution and had brief heat transfer analysis.Finally,the factors influencing the heat transfer of the two-dimensional analytical model are analyzed.The results show that: in the actual project,there exists the best circulating fluid flow and the best heat exchanger water supply temperature;the various types of heat transfer models established can be applied to the actual engineering in severe cold areas.therein the semi-empirical design calculation model can be used to obtain the number of design wells required,the design depth of wells,the meter of heat exchange and other parameters in the preliminary design stage;the two-dimensional analytical model can be used to analyze the influence factors of heat transfer factors,for example,the results,that research the two factors of the thermal conductivity of the inner and outer pipe,show that the influence of the two on the outlet fluid temperature of the heat exchanger is particularly large in the low thermal conductivity range,In addition,the experimental results show that the model can also accurately deduce the average thermal conductivity of the soil in the severe cold area,but the average volume of the geothermal volume is still to be studied;The simulation results of the numerical model are in line with the engineering practice,providing an effective solution for the similar heat transfer problem,and the model can be used to carry out more accurate analysis of heat transfer.In this study,the original ground temperature distribution data and some hydro-geological data of Harbin were obtained through experimental tests,which provided the basis for the subsequent development of similar projects to a certain degree.