Abstract

An original method of calculating isochoric and isobaric heat capacity based on the fundamental relationships of thermodynamics is presented. The theoretical development of the methodology for calculating isochoric and isobaric heat capacity can be used to obtain high metrological data on the thermophysical properties of new low-boiling working substances of power plants operating on the Rankine organic cycle and to replenish existing databases. The technique allows the use of heterogeneous experimental results of acoustic and thermal measurements to calculate the basic thermodynamic functions without information about the values of ideal gas functions, and also to evaluate the consistency of experimental data. Formulas are derived for calculating isobaric and isochoric heat capacities, which are based on reliable equations describing experimental data on the speed of sound and density depending on state parameters. The method was tested using both the characteristics of the reference substances (H₂O and CO₂), and own new experimental data on the thermal and acoustic properties of octafluorocyclobutane (c-C₄F₈) in the liquid phase for temperatures of 320 and 340 K and pressures from 4 to 10 MPa. The isochoric heat capacity was calculated from measurements of the density of octafluorocyclobutane and the speed of sound in it. According to the latest series of density measurements in a limited region of the states of the liquid phase of octafluorocyclobutane obtained by the constant volume piezometer method, the isochoric heat capacity was calculated using the equation proposed in this work. The uncertainty of the experimental data used for the test calculation of the density did not exceed 0.25%, and the speed of sound did not exceed 0.05%. The standard deviation in the description of the dependence of thermal quantities was 0.23%, and acoustic—0.15%.

中文翻译：

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利用联合热声测量结果计算某些热力学函数的技术

摘要

提出了一种基于热力学基本关系的等压和等压热容计算方法。用于计算等容和等压热容量的方法的理论发展可用于获得有关朗肯有机循环下运行的电厂新型低沸点工作物质的热物理性质的高计量数据，并补充现有数据库。该技术允许使用声学和热测量的异质实验结果来计算基本热力学函数，而无需有关理想气体函数值的信息，也可以评估实验数据的一致性。导出了用于计算等压和等容热容量的公式，它们基于可靠的方程式，该方程式描述了根据状态参数确定的关于声速和密度的实验数据。使用参考物质（H₂ O和CO ₂），并拥有有关八氟环丁烷（c -C ₄ F _8）的热和声性质的新实验数据。）在液相中，温度为320和340 K，压力为4到10 MPa。通过测量八氟环丁烷的密度和其中的声速来计算等容热容。根据通过恒定体积压强计法获得的八氟环丁烷液相状态的有限区域中的最新密度测量系列，使用本文提出的公式计算了等容热容。用于密度的测试计算的实验数据的不确定性不超过0.25％，并且声速不超过0.05％。热量相关性描述中的标准偏差为0.23％，声学值为0.15％。