介质物态变化对超低温阀门降温效果的影响

Influence of medium state change on cooling effect of ultra-low temperature valve

深入研究超低温阀门的关键技术,对提高我国特种阀门技术具有深远影响。在仿真模拟超低温阀门温度分布时,采用的分析方式忽略了低温介质吸收热量发生相变后,所产生的低温气体与阀门之间的热量传递。为此,以Class300-DN65超低温截止阀为例,研究了稳态工作过程中介质物态变化及相变产生的低温气体对阀门降温效果的影响。首先,对绝热状态下介质流动的过程进行了计算流体动力学(CFD)仿真模拟,并建立了其传热学模型,以解释热量的传递过程;然后,研究了发生热量传递时阀盖内部间隙、以及阀体内流场介质物态分布规律;最后,根据稳态流-热耦合分析了阀门的温度分布情况。研究结果表明:由液化天然气闪蒸以及汽化产生的低温气体会在阀盖内部空腔底部流动,不断与阀盖、阀杆对流换热,从而对其进行降温。未考虑低温气体对阀门结构温度场的影响时,填料函底部温度为10.6℃;考虑低温气体时,填料函底部温度仅为-0.2℃。因此,设计超低温阀门时需要考虑低温气体对阀门的降温效果,否则容易导致密封失效。

In-depth research on key technologies of ultra-low temperature valves has far-reaching impact on improving special valve technologies in China.When the temperature distribution of the ultra-low temperature valve was simulated,the analysis method used ignored the heat transfer between the low-temperature gas and the valve after the low-temperature medium absorbed the heat and underwent phase change.Therefore,taking Class300-DN65 ultra-low temperature cut-off valve as an example,the influence of medium state change and low temperature gas produced by phase change on valve cooling effect during steady-state operation was studied.Firstly,computational fluid dynamics(CFD)simulation of the medium flow process under adiabatic condition was performed,and a heat transfer model was established to explain the heat transfer process.Then,when heat transfer occurred,the internal clearance of the valve cover and the media distribution law of the flow field inside the valve were studied.Finally,the temperature distribution of the valve was analyzed by steady-state flow-thermal coupling.The research results show that the low temperature gas generated by evaporation and vaporization of LNG will flow at the bottom of the internal cavity of the valve cover,and constantly cool down the valve cover and stem by convective heat exchange,and the bottom temperature of the stuffing box is 10.6℃when the effect of low temperature gas on the temperature field of the valve structure is not considered;but the bottom temperature of the stuffing box is only-0.2℃when the low temperature gas is considered.Therefore,when designing the ultra-low temperature valves,it is necessary to consider the effect of cryogenic gas on the cooling of the valve,which otherwise may lead to seal failure.