The Effect Of Stratification To The Evaporation Properties Of Type C Independent Tank

Liquefied Natural Gas(LNG)has attracted wide attention and is considered to be a sustainable fuel,most of which is stored in low temperature storage tanks at-163℃.In the process of low-temperature storage,LNG evaporation will inevitably occur due to heat leakage from the outside.At the same time,the multi-component of LNG will lead to spontaneous thermal stratification in the tank during evaporation.This stratification will evolve continuously with the evaporation process.After a period of time,it may occur rolling,resulting in a large number of flash vapors instantaneously,which will cause the safe storage of LNG.The evaporation performance of cryogenic fluids in stratified state is of great value in engineering application.Based on the 1.5m~3 independent type C cryogenic tank,the effect of stratification on evaporation performance is investigated by combining physical experiment with numerical simulation.The main work includes three parts:First,using liquid nitrogen as working fluid,the free evaporation process of a 1.5m~3independent type C tank was simulated based on the experimental model.The results show that the relative error between the experimental and numerical simulation values of average daily evaporation rate is 6.75%.The data of temperature monitoring points obtained from the experiment are consistent with the data obtained from numerical simulation,and the relative error is less than 4%.Within the allowable error range of the project,it can be considered that the model and algorithm meet the requirements of evaporation rate prediction.Then,the evolution process of stratification is studied in detail by using the two-dimensional tank model.The influence of initial filling rate on evaporation performance in static stratification was analyzed.The results show that the time needed for stratification to roll increases with the increase of initial filling rate,and the roll duration increases with the increase of initial filling rate.Based on this,a method for predicting the time of stratified evolution and the maximum evaporation rate during rollover in an independent C-type tank is proposed.The numerical simulation data of evaporation rate are compared with the experimental data of hourly evaporation rate in segments.The results show that the trend of evaporation rate is basically the same,and the relative error of stratified evolution time and maximum evaporation rate is controlled within 15%,which proves that the model is in accordance with the experimental data.The algorithm can predict the time needed for stratification to roll and the peak evaporation rate of flash vapor caused by roll of an independent type C cryogenic tank.Finally,the effect of stratification on evaporation performance of 1.5m~3 independent type C tank under sloshing condition is analyzed.The effect of stratification on evaporation rate under different sloshing frequencies and amplitudes was investigated.The results show that when the amplitude of sloshing is fixed and the excitation frequency is near the natural frequency,the maximum evaporation rate considering the delamination is about 20%higher than that without considering the delamination at the same time,and the time required for the delamination to evolve to rollover is obviously shortened.When the excitation frequency is far away from the natural frequency,the maximum evaporation rate with stratification is about 5%higher than that without stratification at the same time.The time required for stratification to rollover is shortened with the increase of frequency.When the sloshing frequency is fixed and the magnitude is natural frequency,the maximum evaporation rate considering stratification is about 20%higher than that without stratification at the same time.The overall evaporation rate increases with the increase of amplitude,and the time required for stratification to roll increases with the increase of amplitude.