Measurement of the (p, $\rho$, T) Properties for Pure Hydrocarbons at Temperatures up to 600 K and Pressures up to 200 MPa

Abstract

The data available for the thermodynamic properties of propane, $n$-butane, and isobutane at temperatures above 440 K are outdated and show significant discrepancies with each other. The ambiguity associated with these data could be limiting to the development of any understanding related to the effects of mixing of these substances with other materials such as $\text{ CO}_{2}$, ammonia, and non-flammable or lower-flammable HFC refrigerants. In this study, the (p, $\rho$, T) properties of propane, $n$-butane, and isobutane were measured at temperatures ranging from (360 to 600) K and pressures ranging from (50 to 200) MPa. Precise measurements were carried out using a metal-bellows variable volumometer with a thermostatted air bath. The expanded uncertainties $(k = 2)$ in the temperature, pressure, and density measurements were estimated to be $<$5 mK, 0.02 MPa, and 0.88 kg $\cdot$ m$^{-3}$ ($T\le 423$ K, $p<100$ MPa), 0.76 kg $\cdot$ $\text{ m}^{-3}$ ($T\le 423$ K, $p\ge 100$ MPa), 0.76 kg $\cdot$ $\text{ m}^{-3}$ ($T>423$ K, $p < 100$ MPa), and 2.94 kg $\cdot$ $\text{ m}^{-3}$ ($T>423$ K, $p \ge 100$ MPa), respectively. The data obtained throughout this study were systematically compared with the calculated values derived from the available equations of state. These models agree well with the measured data at higher temperatures up to 600 K, demonstrating their suitability for an effective and precise examination of the mixing effects of potential alternative mixtures.