Research On Temperature And Thermal Stress Transient Characteristics Of Cryogenic Liquefied Gas Storage Tanks

With the development of our country's economy,the reform of energy structure and the popularization of cryogenic technology,cryogenic liquefied gases,especially liquid-hydrogen(LH2)and other energy gases,have begun to play an important role in China's modernization process.Cryogenic liquefied gas storage tanks(referred to as"cryogenic storage tanks")are the main storage and transportation equipment for cryogenic liquefied gas and are widely used in energy,chemical,petroleum,medical,aerospace and other fields.The filling process of cryogenic liquefied gas is an important part in the use of cryogenic storage tanks.The filling method is directly related to the economics of the filling process and the safety of cryogenic storage tanks.Irregular filling operation can lead to excessive cooling rate and excessive temperature gradient in the cryogenic storage tank during filling,which may cause a large transient thermal stress in the tank and result in the structure of tank invalid.However,there are few studies on the filling process of vertical cryogenic storage tanks,and the previous research focuses on theoretical and numerical simulation methods to study the temperature and pressure distribution in the storage tank,and without further study of the influence of non-uniform temperature field on the tank structure.Considering the volume of vertical cryogenic storage tanks is large,there are many difficulties in on-site experiment,so the thermal-mechanical coupled numerical simulation method is used to study the effects of various parameters,such as the filling mass flow,storage tank volume,length-diameter ratio,on the transient temperature and thermal stress of cryogenic storage tanks.The specific work is as follows:(1)A CFD numerical model was established to simulate the filling process of vertical cryogenic storage tanks,and the rationality of the CFD model was verified by experiments data from literature.The results show that the average relative error of the tank wall temperature at the three monitoring points of T3(temperature monitoring point near the straight edge of the lower head),T9(temperature monitoring point of the center of the cylinder),and T15(temperature monitoring point of the upper head)is 8.63%and the maximum relative error is 14.14%%,which meets the engineering accuracy requirements.Based on the CFD model,a unidirectional thermal-mechanical coupled numerical model was established through ANSYS.(2)By using the CFD model to study the temperature drop characteristics of the cryogenic storage tank during the LH2 filling process,it was found that the internal space average temperature of 50 m3 cryogenic storage tank(tank diameter is 3200 mm,working pressure is 0.7 MPa,and charge mass flow is 8 kg·s-1)will quickly fall from room temperature 295K to low temperature 40K within 8 s of the start of filling.Through a plurality of temperature monitoring points arranged along the axial direction of the storage tank,it can be found that the temperature drop rate of the tank wall gradually decreases from the bottom to the top in the axial direction.(3)According to the established 50 m3LH2 cryogenic storage tank(the tank diameter is 3200 mm,the pressure is 0.7 MPa)CFD and ANSYS numerical model,we can study the effect of filling mass flow on the temperature drop characteristics and thermal stress of the tank wall,it is found that the filling mass flow is faster,the temperature drop of the tank wall at the same location is faster,simultaneously it causes the larger transient thermal stress on the cryogenic tank,and the faster thermal stress reduction rate with time.Under free-constrained conditions,when the filling mass flow rate is 10 kg·s-1,the tank will have a thermal stress peak at the beginning,reaching 243.45 MPa.(4)By studying the effects of tank volume,aspect ratio,and pressure on the temperature drop characteristics and thermal stress distribution of the tank firstly,it found that the tanks have the same temperature drop characteristics under different parameters,and the temperature drop rate at the same position of the tank wall and the maximum transient thermal stress of the tank wall were both proportional to the volume and aspect ratio of the tank,so for large-scale or large aspect ratio cryogenic storage tanks,it is recommended to reduce the filling mass flow rate.