干气密封的实际气体焦耳-汤姆逊效应分析

干气密封系统中气体通过过滤器、阀门、孔板和密封端面等组件时会发生焦耳-汤姆逊（JT）效应，可能导致密封气温度降低，甚至出现液相凝析。焦耳-汤姆逊效应一般通过焦耳-汤姆逊系数来反映。针对干气密封常面临的氢气、氮气、空气和二氧化碳，利用VDW方程、RK方程、SRK方程和PR方程4个经典状态方程（EOS）分别计算了相应的焦耳-汤姆逊（JT）系数，并与文献实验数据进行了比较，选择最佳状态方程作出各气体的JT系数曲线和焦耳-汤姆逊反转曲线（JTIC），并利用编程计算出空气和氮气通过干气密封端面时，由于JT效应引起的气体温降。结果表明：实际气体的焦耳-汤姆逊效应，对干气密封的节流环节会产生重要影响。常温条件下，氢气发生致热效应，而氮气、空气和二氧化碳气体发生致冷效应。采用4种状态方程计算焦耳-汤姆逊系数时，RK方程的平均相对误差和最大相对误差最低且分别小于4%和10%。干气密封气体的实际气体焦耳-汤姆逊效应能引起较大的温度变化，其中气体介质压力比介质温度对温差的影响更大。压力较小时JT效应引起的温降可以忽略。关键词：干气密封；实际气体；状态方程；焦耳-汤姆逊系数；反转曲线

Analysis of Joule-Thomson effect of real gas system sealed by dry gas

In a system sealed by dry gas, the Joule-Thomson (JT) effect occurs when the gas flows through the components of filters, valves, orifices and end faces, which may cause the temperature drop of sealing gas, even the appearance of liquid condensation. Generally, the Joule-Thomson effect is represented by Joule-Thomson coefficient. As to the hydrogen, nitrogen, air and carbon dioxide, which are often encountered for the cases of sealing by dry gas, the corresponding Joule-Thomson (JT) coefficients were calculated by four classical equations of state (EOS) of VDW, RK, SRK and PR. Subsequently, those calculated coefficients are compared with the experimental data in the literatures. The JT coefficient curves and Joule-Thomson inversion curves (JTIC) were plotted using the optimal equation of state. As to air and nitrogen through the end faces of dry sealing gas, the gas temperature drops caused by JT effect were calculated by applying the computer program. It shows that the Joule-Thomson effect of real gas, which have important influence on the throttle of dry sealing gas. At room temperature, hydrogen showed exothermic effect, while nitrogen, air and carbon dioxide endothermic (cooling) effect. The corresponding Joule-Thomson (JT) coefficients were calculated by the four classical EOS, the average relative error and maximum relative error of RK equation were the minimum, less than 4% and 10%, respectively. The JT effect of real gas causes large temperature difference in the dry sealing gas, of which the gas pressure more influences on the temperature drop than the gas temperature does. When the pressure is small, the temperature drop by the JT effect can be negligible.