Study On Thermal And Physical Properties Of Rock Mass Based On Surface Heat Source

With the problem of heat accumulation in subway tunnels gradually emerging,in order to alleviate this problem,the waste heat source heat pump system of subway as a new research direction of ground source heat pump system was put forward by experts.Use the waste heat source heat pump system can be heat absorption and status of the underground space in winter for heating buildings on the ground,underground space of the wall is usually flat or approximate plane,compared with the traditional vertical buried tube heat exchanger,if by plane heat exchanger along the wall laying of underground space,the heat transfer effect is better,more convenient construction.Thermal physical properties of the rock mass around underground space to a great extent,affects the plane design of heat exchanger,and based on existing line heat source and heat source rock thermal physical property test method is not applicable to surface heat exchanger,in order to ensure the design of plate heat exchanger can make full use of waste heat source and cost savings,need accurate location of actual engineering thermal physical parameters of rock mass.This subject mainly studies a method for testing the thermal properties of rock mass based on surface heat source,through which accurate thermal properties parameters are obtained,in order to provide design basis for engineering practice.Firstly,a onedimensional unsteady heat transfer model of surface heat source and rock mass heat transfer is established by simplifying the heat transfer model.Secondly,set up the field thermal property test bench and test it according to the test method.Then,the data obtained from the test of different working conditions were processed and analyzed,and then the heat flux density was found in the middle of the plane heat exchanger.Finally,the thermal and physical parameters of rock mass are obtained through analytical solution by using inversion calculation method,and the thermal and physical parameters are compared with the actual thermal and physical parameters to verify the testing method of thermal and physical properties of rock mass.The test method based on the above contents is as follows:? A 1*2m planar heat exchanger was selected,which was laid on the relatively smooth rock mass wall surface and covered with a layer of insulation cotton isolation and convection heat transfer between air.? Different heating power is selected for testing,and each test lasts no less than 4h.It is suggested that in case of sufficient time,test for about 3-4h after the temperature is stable.? When the next set of heating conditions is carried out,there is no need to cool down again.According to the mobility characteristics of the planar heat exchanger,it can be disassembled and laid in other places to ensure that it is not affected by the temperature of the test site of the first set of working conditions.? When 1 x 2m flat-plane heat exchanger is adopted,the heat transfer in the central part takes up 15% of the total proportion.Then,the heat transfer in the central part is calculated according to the total heat transfer calculated by experiments,and the heat flux per unit area of the central part is calculated.? When the measured rock mass is not supported by a lining,the actual thermal and physical parameters are selected.when the lining support is carried out,the distance of heat transfer when the temperature is stable is calculated by the numerical solution method,so as to obtain the comprehensive thermal conductivity of the rock mass and the injection material.? By using the inversion calculation method,the analytical solution of the heat transfer model is compared with the measured average temperature,and then the optimal value of thermal properties parameters is obtained..? Nine measurement points at the center are selected,and the thickness of the gap between the plane heat exchanger and the wall surface is estimated by the ruler.The average value of nine measurement points is obtained,and then the thermal contact resistance is calculated.In this study,the thermal and physical parameters of rock mass can be obtained accurately,providing a reference basis for the rational design and application of the subway waste heat source heat pump system.