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Vapor phase acoustic measurements for R125 and development of a Helmholtz free energy equation

机译：R125的汽相声学测量和亥姆霍兹自由能方程的建立

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This paper presents speed of sound measurements on pentafluoroethane (R125) in the vapor phase. The measurements were performed in a stainless steel spherical resonator of similar to 900 cm(3) at temperatures in the range 260-360 K and pressures up to 500 kPa. Acoustic virial coefficients and ideal gas heat capacities are deduced directly from the data. The whole set of speed of sound measurements and the ideal gas heat capacities are then correlated in the forms u(2)(T, p) and c(p)(o)(T), respectively. Analytical expressions for the temperature dependencies of the thermodynamic virial coefficients, based on a hard-core square-well potential, are then assumed and the model is fitted to the acoustic data, obtaining a virial equation of state for the vapor phase. A highly accurate Helmholtz equation of state a(rho, T) is established on the basis of the measured data, representing the (p rhoT) surface of the vapor phase in the same temperature and pressure ranges. The ideal gas Helmholtz equation a(o)(rho, T) is obtained from the former c(p)(o)(T) correlation. Given the high accuracy of the equation form, only very precise experimental data, such as acoustic measurements, are suitable for fitting the a(R)(rho, T) equation parameters. Both the thermodynamic models are validated on available density data. The good level of consistency reached by the Helmholtz equation, shows its form to be very reliable. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 20]
机译：本文介绍了在气相中对五氟乙烷（R125）进行声音测量的速度。在类似于900 cm（3）的不锈钢球形谐振器中，在260-360 K的温度和最高500 kPa的压力下进行测量。直接从数据推导出声维里系数和理想气体热容量。然后将整套声音测量速度与理想气体热容量分别以u（2）（T，p）和c（p）（o）（T）的形式进行关联。然后基于铁心方阱势，假定热力学维里系数的温度依赖性的解析表达式，并将模型拟合到声学数据中，从而获得气相的维里状态方程。根据测量数据建立高度精确的亥姆霍兹状态方程a（rho，T），表示在相同温度和压力范围内气相的（p rhoT）表面。理想的气体亥姆霍兹方程a（o）（rho，T）从前一个c（p）（o）（T）相关性获得。鉴于方程式的高精度，只有非常精确的实验数据（例如声学测量）才适合拟合a（R）（rho，T）方程参数。两种热力学模型都根据可用的密度数据进行了验证。亥姆霍兹方程达到的良好一致性水平表明其形式非常可靠。 （C）2000 Elsevier Science B.V.保留所有权利。 [参考：20]

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