Study On The Rule Of Ventless Storage In Cryogenic Tanks

Along with the rapid development of science and the popularization of the cryogenic technology, the cryogenic liquids are widespread in industry. And research on the storage and transportation of cryogenic liquids attracts more attentions.In this thesis, the rule of the lossless storage in the horizontal cryogenic tanks was studied. The subject investigated included liquid nitrogen and liquefied natural gas (LNG). On base of thermodynamic analysis, the dimensionless number Gl was introduced to characterization of the relative heat loss in gas space of cryogenic tank. The Gl number's general rule was obtained through calculating the Gl number using physical property data of different cryogenic liquids. Based on this gas space heat loss theory, and also on the old ventless storage models and the achievements of the layer theory, the new model was established.In the process of calculating the ventless storage duration, lots of physical property calculation was needed. In this thesis, the density, the enthalpy, the viscosity, the conductivity factor, and the phase equilibrium parameter etc. of liquid nitrogen and liquefied natural gas was calculated. The LKP state equation was chose to calculate the density and the enthalpy. For liquid nitrogen, the accurate correlative formula was used to calculate the thermo physical property data. For the viscosity and the conductivity factor of LNG, programs were compiled respect. The programs were applied in vapor phase, liquid phase and critical state. For LNG, program was also compiled to calculate the bubble point temperature, to solve the phase equilibrium problems.In the process of calculating the state parameters of gas space in the tank, the parameters (P, T) need to be solved with (ρ,h). But (P, T) is implicit expression of (ρ,h). The problem can't be solved by simple iterative algorithm, and this problem is so complicated and needs searching roots in the two-dimension space. In this thesis, 25-point method is finally being presented. The 25-poing is based on the concept of Norm and the grid, and solves this two-dimension problem perfectly.In this thesis, a two-cube horizontal cryogenic tank was used to carry out the tests. One time static evaporation rate experiment and four times ventless storage tests were carried out, and the flow data and pressure data in all these tests were recorded. To validate the new model, the calculated values from the model and the data from the tests were checked. Result shows that the calculated values and the tested values were coupled well.At last, the new model was used to study the rule of ventless storage duration under different conditions, include different initial bulk coefficient, different heal loss rate, different tank size, etc. Some useful conclusions were obtained. Also the numerical model used for LNG was used to study the rule of ventless storage duration under different components. The general rule for mixture was obtained.