Study On Formation Mechanism Of Temperature Field Of Liquid Nitrogen Freezing In Coastal Layer

In this paper,based on the origin of the Fuzhou Metro Shield Project,the in-depth study of liquid nitrogen convection heat transfer theory,the physical and mechanical tests of coastal artificial frozen soil and the two-dimensional temperature field of liquid nitrogen freezing on shield left line by ANSYS software.The numerical simulation is carried out,and then compared with the results obtained in the actual project,the formation mechanism of the formation liquid nitrogen freezing temperature field is studied.The main conclusions are:1)The specific heat of various soils is between 0.78 and 1.52 kJ/(kg·℃);the thermal conductivity of the soil at normal temperature is within the range of 1.005～2.232 W/(m·℃),and the thermal conductivity of the soil will increase significantly at low temperatures,generally in the range of 1.654～2.868 W/(m·℃);different formations The freezing temperature is between-0.90℃ and-1.60℃.2)The frost heave force of each layer of frozen soil is in the range of 1.29～1.55MPa,and the frost heave rate ranges from 1.23%to 1.56%.In the classification of frozen soil in China,the soil layer is divided into weakly frozen soil.3)Related studies have shown that there is a significant linear correlation between the uniaxial compressive strength and freezing temperature of frozen soil.When the temperature is decreased by 1℃,the strength of frozen soil will increase 0.112～0.497 Mpa.Therefore,in the actual construction,the method of reducing the average temperature of the frozen wall can be used to enhance the bearing capacity of the frozen wall.4)The freezing time and average temperature of the subway project obtained in this time value simulation are basically consistent with the actual results measured.The measured values in the construction of the project are compared with the results of the numerical simulation.If there is a large difference,it needs to be adjusted in time.5)In this case,the fourth day of the active freezing period of liquid nitrogen has reached the designed frozen wall thickness of 1.8m,which is 3 days earlier than the original design time.Because of the freezing fastness,low temperature and high strength,liquid nitrogen freezing has the characteristics of If the design is not optimized,the thickness of the frozen wall will be greater than the design thickness,and it is easy to form an excessive frost heaving hazard.In addition,the cost of liquid nitrogen freezing is large,and energy loss is easy to occur.Currently,there is a lack of a standardized liquid nitrogen temperature field simulation method in this respect.In this paper,the liquid nitrogen freezing problem is studied.The finite element calculation model of liquid nitrogen temperature field is designed.The simulation results are compared with the actual engineering data.The simulation data is used to provide reference for such engineering.Liquid nitrogen should be used as efficiently as possible to save energy and improve the economic benefits of the project.Figure[52]Table[19]Reference[70]...