Study On Pre-cooling Heat Transfer Mechanism Of Cryogenic LNG Corrugated Hose

Cryogenic LNG corrugated hose is the key equipment for realizing offshore natural gas exploitation and transportation.Its pre-cooling mechanism is complex,and the precooling effect is affected by many factors.In this work,the problem of pre-cooling heat transfer mechanism of cryogenic LNG corrugated hose is studied by method of theoretical calculation and finite element model.The influences of the thickness of cold insulation layer,the inlet speed of nitrogen and the radius of the hose are analyzed.The main research work of this paper is summarized as follows:(1)According to the basic control equation,heat transfer control equation and fixed solution conditions,a mathematical model of pre-cooling heat transfer of cryogenic LNG corrugated hose is established,and the convective heat transfer coefficient between the inner wall of the hose and the nitrogen gas is accurately solved.The established heat transfer differential equation and boundary conditions are solved discretely based on the finite difference method.The transient heat transfer process in the pre-cooling start-up stage is analyzed by iterative solution.Then,some optimization suggestions are given for the pre-cooling start-up stage of the hose based on the axial temperature distribution of the inner wall and the radial temperature distribution of the cold insulation layer.(2)The turbulence models are systematically introduced and the model is selected according to the characteristics of the problem in this work.The numerical analysis physical model is established with reference to the cryogenic LNG corrugated hose produced by Nexans.Also,the calculation settings and independence test of the model transient step size are carried out.Then,the numerical simulation results of pre-cooling heat transfer of cryogenic LNG corrugated hose are analyzed.The transient heat transfer in the pre-cooling start-up stage is completed,the axial and radial temperature distribution nephograms and the temperature change curves are obtained through the analysis.Then,the influences of the thickness of the cold insulation layer,the speed of nitrogen and the radius of the hose on the pre-cooling heat transfer are analyzed.The heat transfer mechanism of pre-cooling is studied and optimization suggestions are given for the precooling process.(3)The theoretical method is used to analyze the pre-cooling heat transfer mechanism of cryogenic LNG corrugated hose.The heat transfer control equations of nitrogen and cold insulation layer are established.Then,the method of numerical integration is used to solve the average temperature of the section and the heat transfer control differential equations.Also,the temperature equation of the cold insulation layer under the pre-cooling stable operation condition,which is changed by time and space position is obtained by the theoretical method.The temperatures of the inner wall and the cold insulation layer are calculated,and the theoretical results are compared with the numerical simulation results.The accuracy of these two results is verified by doing so.The sensitivity analysis method is used to study the influences of the thickness of the cold insulation layer,the speed of nitrogen and the radius of the hose.The research work of this paper can provide useful guidance for the pre-cooling process optimization of cryogenic LNG corrugated hose.