Numerical Simulation And Experimental Study Of Flooding Process Of LN₂-VN₂

Flooding is widespread in many industrial applications such as cryogenic distillation columns,cryogenic heat exchangers and pre-cooling pipelines.It's occurrence often deteriorates the regular operation of industrial equipment.Due to the differences of physical property,the flooding mechanisms of LN₂-VN₂ and water-air are different.Unlike the normal fluids,which have been deeply studied by researchers,there is still a shortage of exploration for cryogenic fluids about the topic of flooding.In this paper,numerical and experimental methods are both utilized to explore the flow characteristics and physical regulations of flooding of LN₂-VN₂.The AIAD drag-force model has been used by many scholars to study the multiphase flow at room temperature.The drag coefficient of AIAD scheme is closely related to physical properties such as fluid density,shear stress distribution and volume fraction distribution.In this paper,the influence of physical properties on the drag coefficient is clarified.And the modification of AIAD model for the LN₂-VN₂ is carried out basing on the physical properties.It's the first time that the AIAD model has ever been modified for cryogenic applications.The numerical simulation of flooding phenomenon of LN₂-VN₂ is carried out basing on the modified AIAD model.And after comparing the numerical results with previous experimental data,the applicability of modified AIAD model for cryogenic multiphase flow is verified.We have obtained the LN₂-VN₂ flooding velocity for the first time with numerical methods,and explored the influences of geometric factors such as the pipe diameter,pipe length and inclination.It has been observed that the LN₂-VN₂ flooding process is often accompanied by“spray entrainment”and liquid backflow phenomenon.Comparison between LN₂-VN₂ and water-air shows that the flooding velocity of LN₂-VN₂ is always much lower.The improvement work of vacuum system is implemented on the previous experimental apparatus to improve the performance of thermal insulation system.Experiment work of flooding of LN₂-VN₂ is carried out under multiple inclinations.It's found that the flooding velocity obtained by experiment and calculation are in a good agreement,and the error between them is less than 15%.