利用跨接SRK状态方程计算CO2的热力学性质

Calculation of the thermodynamic properties for CO2 by crossover SRK EoS

中文关键词: SRK状态方程  跨接模型  近临界区  二氧化碳

英文关键词: SRK EoS  crossover model  critical region  carbon dioxide

中文摘要:

      CO2在近临界区的热力学性质的计算是超临界二氧化碳（S-CO2）工程应用的基础。基于平均场理论的立方型状态方程无法描述由于临界涨落引起的临界点附近的流体热力学性质的奇异性，需要引入跨接模型。基于Kiselev方法，本文建立了CO2的跨接SRK方程，在跨接方程中使用显式跨接函数以提高计算效率，计算了CO2的相平衡性质、单相区的pvT性质、比热容以及音速。结果显示，本文的跨接方程明显改进了原SRK方程对于饱和液相密度及液相区和超临界区pvT性质的计算，其中饱和液相密度计算和饱和气相密度计算平均绝对相对偏差分别提高了11.51%和1.49%，临界比定压热容cp、临界比定容热容cv和临界音速u分别提高了9.25%，8.72%和5.01%；跨接方程可正确描述比热容及音速在临界点的渐近奇异行为。

英文摘要:

      The calculation of the thermodynamic properties of CO2 in the critical region is the basis for the engineer-ing application of supercritical carbon dioxide (S-CO2). The cubic EoSs based on the mean field theory cannot describe the singularity of the thermodynamic properties of the fluid near the critical point caused by the critical fluctuations, and a crossover model needs to be introduced. Here, based on the Kiselev’s method the crossover SRK EoS for CO2 was established. The explicit crossover function was used in the crossover SRK EoS to improve calculation efficiency. The phase equilibrium properties, the pvT properties in the single-phase region, the heat capacity and the speed of sound for CO2 were calculated using both crossover SRK EoS and SRK EoS. The calculation results show that, the crossover SRK EoS in this paper has significantly improved the description accuracy of original SRK EoS for the saturated liquid density and the pvT properties in the liquid and supercritical regions. The average absolute relative deviations of saturated liquid density and saturated gas density are increased by 11.51% and 1.49% respectively, and the critical specific constant pressure heat capacity cp, critical specific constant volume heat capacity cv and critical sound speed u are increased by 9.25%, 8.72% and 5.01% respectively. The equation proposed here can accurately de-scribe the divergence behavior of heat capacity and speed of sound at the critical point for CO2.