零重力条件下低温射流抑制大尺寸液氢储罐热分层的数值研究

液氢是一种常用的沸点低、易蒸发的空间低温推进剂. 空间微重力环境中浮力对流被极大减弱,当推进剂储罐壁面存在局部漏热时,储罐内部气液两相流体系会出现环绕漏热源的热分层现象,引起局部过热沸腾,导致储罐内部压力急剧增大,危害系统结构安全. 利用低温射流抑制储罐热分层现象是一种有效手段. 低温流体通过设置在储罐内部的射流喷嘴与储罐内部的流体混合,消减局部高温,实现温度的均匀化. 采用全充满的二维大尺寸储罐模型,对零重力条件下液氢储罐内局部漏热引起的热分层现象开展了数值模拟,主要分析了位于靠近储罐底部的漏热带以及出口衔接段漏热带漏热形成的局部热分层现象的抑制和消除,并研究了不同低温射流条件对于消除零重力条件下液氢储罐内部热分层效果的影响. 研究结果表明对于大尺寸储罐,当采用圆形射流喷嘴且低温射流条件相同时,射流喷嘴的位置对罐体内部热分层消除效果影响不是很明显. 当射流喷嘴位于储罐内部同一相对位置且入射流量相同时,圆形射流喷嘴因出流方向更集中,罐内流场演变更快,消除热分层比半球形射流喷嘴更有效. 

NUMERICAL STUDY ON THERMAL DESTRATIFICATION IN LARGE SCALE HYDROGEN PROPELLANT TANK IN SPACE BY JET INJECTION UNDER ZERO GRAVITY CONDITION

Liquid Hydrogen plays a vital role in the future energy system as a space propellant, but it is sensitive to heat leakage from the environment because of its low boiling point and easy evaporation. On the other hand the buoyancy convection in the space microgravity environment is significantly reduced. When there is local heat leakage on the wall of the propellant tank, temperature stratification arises around the heat leakage source causing local overheating. It seriously affects the multiphase heat and mass transfer in the propellant tank which induces the tank pressure rise and jeopardize the structural safety of the system. To prevent the tank pressure from rising above the design of limits, venting or active pressure control techniques must be implemented. The cryogenic jet mixing is an effective means to suppress temperature stratification. The cryogenic fluid is mixed with the fluid inside the tank through a jet nozzle to reduce the local high temperature and achieve uniform temperature. In present paper, the thermal stratification phenomenon caused by the local heat leakage under microgravity condition was numerically simulated by using a fully filled two-dimensional large scale tank model. This paper mainly analyzes the suppression and elimination of local thermal stratification caused by heat leakage near the bottom of the storage tank and the outlet connecting section. The influence of different cryogenic jet mixing conditions on eliminating the temperature stratification effect is analyzed. The results show that the position of jet nozzle has no obvious effect on the elimination of thermal stratification inside the tank when the circular jet nozzle is used and the cryogenic jet condition is the same. When the jet nozzles are located in the same relative position inside the tank and the incident flow rate is the same, the circular jet nozzles have more concentrated flow direction, the flow field in the tank evolves faster, so the thermal stratification elimination effect is better than the hemispherical jet nozzles.