Experimental Study On Geothermal Properties Of Coaxial Deep-well Casing-shaped Underground Heat Exchanger

With the continuous development of urban and rural construction in China,the construction of centralized heating is growing,the energy consumption of construction is increasing.According to statistics in the total energy consumption,the construction of energy consumption accounted for nearly 30% of the total domestic energy consumption ratio.In the building of energy consumption,heating air conditioning on energy consumption can reach about 55%.So one of the key directions to reduce building energy consumption is to solve the problem of heating air conditioning energy consumption.Improve the comprehensive utilization efficiency of air conditioning cold and heat source system can effectively reduce the energy consumption of air conditioning systems.Ground source heat pump system is a kind of energy efficient air conditioning cold and heat source system.In this paper,the heat transfer performance of the Coaxial deep-well Casing-shaped ground source heat pump system and the thermal and physical parameters of the geothermal heat transfer are studied.In this paper,the linear heat source model is used to analyze the heat transfer process of the coaxial deep well casing heat exchanger from the inside and outside,and the theoretical calculation results of the thermal resistance of each layer in the heat transfer process are obtained.And the minimum flow rate of the circulating fluid in order to ensure the flow state of the circulating fluid in the buried pipe is turbulent.Secondly,according to the large amount of heat transfer in single well of coaxial deep well heat exchanger,the water flow is hot spot of water resistance,the geothermal thermal response testing equipment is designed and developed.The equipment includes high-power heaters,high-lift circulating pumps and the necessary recording instruments.The main contents of the test includes:(1)Using the instrument to carry out the actual project of coaxial deep well casing with geothermal thermal response test.(2)According to the experimental results of the project,the thermal conductivity,the specific heat capacity of the volume and the heat transfer capacity of the heat exchanger in the unit length are analyzed by the slope method.(3)And the weight of the thermal resistance of each layer of the test drilling is calculated according to the thermal physical parameters of the soil.(4)The underground temperature field of casing buried pipe is numerically simulated by Fluent software,and the distribution of undergroundtemperature field at different operating time is obtained.(5)The thermal properties of the geothermal data were verified by the thermal response experiment,and the deviation between the thermophysical properties parameters and the actual boundary conditions was calculated by the slope method.