Critical parameters for propane determined by the image analysis

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Abstract

The (p, ρ, T) measurements and visual observations of the meniscus for propane were carried out carefully in the critical region over the range of temperatures: −60 mK  (T  Tc)   40 mK and of densities: −4 kg · m−3  (ρ  ρc)  6 kg · m−3 by a metal-bellows volumometer with an optical cell. Vapour pressures were also measured at T = (320.000, 343.132, 369.000, and 369.625) K. The critical point of Tc, ρc, and pc was determined by the image analysis of the critical opalescence. Comparisons of the critical parameters with values given in the literature are presented.

Introduction

In previous publications [1], [2], we reported measurements of thermodynamic properties of propane in the compressed liquid phase between the temperatures (280 and 400) K at pressures up to 200 MPa by a metal-bellows variable volumometer. In this paper, the results of vapour pressure measurements, (p, ρ, T) measurements, and visual observations of the meniscus for propane in the critical region using an optical cell and a metal-bellows volumometer are presented. The critical parameters were determined by the image analysis [3] of the critical opalescence. Comparisons of the critical parameters with values given in the literature [4], [5], [6], [7], [8], [9], [10], [11], [12], [13] are also reported.

Section snippets

Materials

The propane was supplied by the Takachiho Chemical Industrial Co., Ltd., Ibaragi, Japan, and its mol-fraction purity was specified by the supplier to be 0.99997. The sample to be loaded was degassed five times by freeze–thaw cycling with liquid nitrogen before loading. The sample loaded in this study is supplied by the same cylinder as the previous work [1], [2] used.

Apparatus and experimental procedure

The measurements were carried out using an optical cell and a metal-bellows volumometer in a pressure vessel. The apparatus and

Results and discussion

We measured the vapour pressure for propane at T = (320.000, 343.132, 369.000, and 369.625) K with different positions of the meniscus to confirm no impurity effect. The mean values of these measurements are given in table 1. Comparison of the present vapour pressure measurements with the experimental data by Miyamoto and Uematsu [1] and Thomas and Harrison [8] is also given in table 1. The present values are in good agreement with those data within the present uncertainties, although the pressure

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