超临界水射流焦汤系数计算与节流过程降温效果分析

The calculation of Joule Thomson coefficient of supercritical water jet flow and the analysis on cooling effect in the process of throttling

高温流体通过喷嘴是节流流动的过程,会引起流体内部温度的变化,将影响高温射流冲击力与热裂解效应等。应用超临界水物性方程与焦汤系数的定义公式,推导出了射流通过喷嘴过程的焦耳汤姆逊系数的求解公式,并编制程序迭代求解,得到不同参数条件下焦耳汤姆逊系数分布特性与变化规律,并采用焦汤系数计算公式,计算得到不同参数下过喷嘴节流过程中降低温度值的变化规律。结果表明,在25~65 MPa和650~1 000 K的条件下,焦耳汤姆逊系数为正,随着反应腔内温度的增加,焦耳汤姆逊系数先增大后减小,在文中条件下的最大值为4.92;而随着反应腔内压力的增加,焦耳汤姆逊系数降低,在65MPa,650 K条件下取得最小值0.22。焦汤效应的最大值均出现在过热蒸汽区,且随着温度的增加,最大值偏离分界线。在射流喷射过程中,温度压力降低值不可忽略,文中条件下最大可达73.5 K,应当合理设置反应腔内温度压力值,降低高温射流通过喷嘴过程的温度损失。

It is a process of throttling flow when high-temperature fluid flows through nozzles.It can change the internal temperature of fluid,and consequently impact the impact force and thermal cracking effect of high-temperature jet flow.In this paper,the formula for calculating Joule Thomson coefficient during the running of jet flow through the nozzle was deduced by applying the definition formulas of physical property equation and Joule Thomson coefficient of supercritical water.Then,a program was prepared for iteration calculation to figure out the distribution characteristics and change laws of Joule Thomson coefficient for different parameters.Finally,Joule Thomson coefficient calculation formula was adopted to calculate the change laws of temperature drop corresponding to different parameters in the process of nozzle throttling.It is indicated that Joule Thomson coefficient is positive under the condition of25to65MPa and650to1000K.As the temperature inside the reaction chamber increases,Joule Thomson coefficient increases first and then decreases.And its maximum value is4.92in the conditions described in this paper.As the pressure inside the reaction chamber increases,Joule Thomson coefficient decreases and reaches the minimum0.22,under the condition of65MPa and650K.Maximum Joule Thomson effect occurs at superheated steam zones,and deviates from the boundary line with the increasing of temperature.Temperature and pressure drops shall not be neglected during the jetting of jet flow.And its maximum could reach73.5K in the conditions described in this paper.Therefore,it is necessary to set rationally the temperature and pressure inside the reaction chamber so as to decrease the temperature loss of high-temperature jet flow when it runs through the nozzle.