Experimental Study On Heat Transfer Of High Thermal Conductivity Concrete Energy Pile

Excessive carbon emissions lead to global climate change,global temperature rise and air pollution has become one of the biggest challenges of mankind in the 21 st century.Ground source heat pump technology is the most potential technology to reduce building carbon emissions and realize green building.In order to overcome the shortcomings of traditional ground source heat pump technology,a new type of vertical buried pipe ground source heat pump system energy pile was born,that is,the heat exchange pipe of the ground source heat pump was placed in the building pile foundation,and the heat exchange between the upper building and the shallow geothermal was made through the heat exchange pipe and circulating liquid,so as to achieve the purpose of refrigeration and heating.At present,the main problem in the application and promotion of energy pile is the low thermal conductivity of concrete,which seriously restricts the heat exchange efficiency between energy pile and surrounding soil.In order to effectively improve the heat transfer efficiency of energy piles,this paper proposes a high thermal conductivity concrete energy pile mixed with silicon carbide.Using indoor model test research and theoretical analysis,the heat exchange performance of the high thermal conductivity concrete energy pile is evaluated.The main research work is as follows:(1)The research on the mix ratio of high heat conduction concrete is carried out.Silicon carbide material is selected as the heat conduction reinforcing material to make the concrete.The water cement ratio,silicon carbide content and water reducing agent content are used as the design parameters of the high heat conduction concrete.The mix ratio test is carried out by three factors and three levels orthogonal test.The results show that the thermal conductivity of concrete can be improved by adding silicon carbide.When the content of Si C is increased from 0 to 15%,the thermal conductivity of concrete is increased by about 105%,2.36w/m · K.;the main factors affecting the thermal conductivity of concrete are water cement ratio and silicon carbide content.Among them,the influence of various factors on the thermal conductivity is silicon carbide content > water cement ratio > water reducing agent Quantity.In addition,on the premise of ensuring the mechanical properties of concrete,the mix ratio is optimized from the point of view of improving the thermal conductivity of concrete.It is suggested that a should be adopted .The combination of water and glue is0.44,the content of water reducing agent is 0.3%,and the content of silicon carbide is15%.(2)In this paper,the heat conduction mechanism of Si C high thermal conductivity concrete is studied.Firstly,the prediction model of thermal conductivity of concrete is analyzed,and then the micro experimental analysis of the test block is carried out.The results show that: the parallel series model can better predict the thermal conductivity of Si C concrete;the thermal conductivity of concrete is greatly affected by porosity,and the smaller the porosity is,the greater the thermal conductivity of concrete is.(3)The thermal response test of Si C high thermal conductivity concrete energy pile was carried out,and the effects of pile material,operation mode and soil saturation around the pile on the heat transfer performance of energy pile were studied in detail.The results show that: the heat transfer efficiency of energy pile made of Si C high thermal conductivity concrete can be significantly improved,and the heat transfer per linear meter of energy pile is about 20% higher than that of ordinary concrete energy pile;the intermittent operation mode of energy pile can also effectively improve the heat transfer efficiency of energy pile;the working efficiency of energy pile in unsaturated soil will increase with the increase of soil saturation.When the silty soil is dried to saturation,the heat transfer per linear meter of the energy pile increases about82%,and when the silt from drying to saturation,the heat transfer per linear meter of the energy pile increases about 90%.(4)The numerical simulation of heat transfer model of energy pile is carried out.The linear heat source model of energy pile,hollow cylinder heat source model,solid cylinder heat source model and constant temperature model of inner wall of heat exchange tube are established respectively.The simulation calculation of experimental results of high thermal conductivity concrete energy pile unit body is carried out.The results show that the traditional constant heat source model has a large error in analyzing the heat transfer characteristics of the unit pile,while the model considering the constant temperature of the inner wall of the heat exchange tube can better simulate the energy pile unit test.