热力学排气系统中节流效应及其冷量利用分析

Analysis on Throttling Effect and Cooling Capacity Utilization in Thermodynamic Vent System

为更好地理解热力学排气系统(TVS)的运行机理,优化其运行参数,针对节流装置,建立了热力学模型,讨论了节流过程中状态参数的变化规律,对比了单相气体、单相液体节流的性能特性,进一步揭示了焦汤节流效应的原理,分析了不同节流背压下节流前低温工质(液氢和液氧)压力和温度对节流性能的影响,并结合TVS实际应用,阐述了节流最大制冷量的利用效果,提出了优化的TVS工作区间。研究表明:在节流过程不发生相变情况下单相气体节流制冷效应要比单相液体节流制冷效应更加显著;而在节流过程发生相变情况下液体节流至两相后,由于空化吸热导致流体温度降低,对于液氢,0.5MPa的压降可产生接近3 K的温降。对于液体节流,节流前压力对节流过程影响可忽略,而节流前温度和节流背压对节流过程起主导作用;对于液氢在在轨运行工况下,考虑到节流制冷量的充分利用,同时保证换热过程体积含气率不高于90%,推荐TVS系统中节流背压范围为75~143 kPa。

In order to understand the operation mechanism of a thermodynamic vent system(TVS) better and optimize its operating parameters, a thermodynamic model is established for a throttling device. The variations of the state parameters during throttling are discussed. The throttling performance of single-phase gas and single-phase liquid is compared. The effects of the pressure and temperature of the pre-throttle fluid(hydrogen and oxygen) on the throttling performance under different throttling back-pressures are discussed and the principle of the Joule-Thomson effect is further revealed. In combination with the practical application of TVS, the utilization of the maximal throttling cooling capacity is illustrated and an optimized TVS operating interval is proposed. The results show that the cooling effect of single-phase gas throttling is more significant than single-phase liquid in the case of no phase change in the throttling process;the temperature of the liquid throttling to the two-phase must be reduced, the latent heat of the two-phase fluid can be utilized, and thus the available cooling capacity is larger;as the heat absorption through gasification leads to the decrease of the fluid temperature such that the pressure drop of 0.5 MPa can produce a temperature drop close to 3 K for liquid hydrogen. For liquid throttling, the pre-throttle temperature and the throttling back-pressure play the leading role in the throttling process, while the pre-throttle pressure can be neglected. Considering the full utilization of throttling cooling capacity and a guarantee of no higher than 90% gas volume fraction for heat exchange, TVS is recommended to have throttling back pressure range of 75-143 kPa for hydrogen under the in-orbit operation.