液舱旋转射流气体惰化特性分析

Analysis of Gas Inerting Characteristics of Swirling Jet in Liquid Tank

针对LNG液舱壁惰化死角难以惰化、惰化进程监测误差大导致惰化效率低的问题,对C型独立液舱的气体惰化特性进行分析。建立数值模拟模型,分析舱内氧气体积分数及等值面分布形态、体积置换次数、惰化完成时间,比较旋流强度、进气速度和直径占比对惰化过程的影响,探讨其气体惰化特性。结果表明:随着旋流强度增大,惰化完成时间先缩短后延长再缩短,当旋流强度为1.0或1.5时去除惰化死角效果明显,且惰化完成时间短、耗气量少。增加惰性气体进气速度和提高直径占比,可以明显消除惰化死角且缩短惰化完成时间、减少耗气量。对惰化过程监测,采用出口平均氧气体积分数来判断惰化完成情况会造成误判,出口平均氧气体积分数降低至2%的时间与舱内最大氧气体积分数降低至2%的惰化完成时间的最大相对偏差为25.53%,最小相对偏差为1.40%,平均相对偏差为7.00%。因此,建议监测出口平均氧气体积分数,但是应在出口氧气体积分数达到2%后继续延长30%惰化时间,确保舱内最大氧气体积分数达标。

Aiming at the problems that the inerting dead corners of LNG liquid bulkhead are difficult to be inerted and the inerting efficiency is low due to the large monitoring error of inerting process,the gas inerting characteristics of C-type independent liquid tank are analyzed.A numerical simulation model is established to analyze the oxygen volume fraction and isosurface distribution,number of volume replacement and inerting completion time in the tank.The effects of swirl intensity,inlet velocity and diameter ratio on the inerting process are compared,and the gas inerting characteristics are discussed.The results show that with the increase of swirl intensity,the completion time of inerting is shortened first,then extended and then shortened.When the swirl intensity is 1.0 or 1.5,the effect of removing inerting dead corners is obvious,and the completion time of inerting is short and the gas consumption is low.Increasing the inert gas inlet speed and increasing the diameter ratio can significantly eliminate the inerting dead corners,shorten the completion time of inerting and reduce gas consumption.For the monitoring of inerting process,using the average oxygen volume fraction at the outlet to judge the completion of inerting will cause misjudgment.The maximum relative deviation between the time when the average oxygen volume fraction at the outlet is reduced to 2%and the time when the maximum oxygen volume fraction in the tank is reduced to 2%is 25.53%,the minimum relative deviation is 1.40%,and the average relative deviation is 7.00%.Therefore,it is recommended to monitor the average oxygen volume fraction at the outlet,but the inerting time shall be extended by 30%after the oxygen volume fraction at the outlet reaches 2%to ensure that the maximum oxygen volume fraction in the tank meets the standard.