Abstract
Among the various thermophysical properties, critical temperature and density are the most basic quantities of state. A determination method of these properties is studied, which uses a digital-image processing for the image around the vapor-liquid phase boundary of sample fluid near the critical point. Critical temperature and density can be determined on the basis of quantitative measurements. Conventional method was based on the personal observation of the meniscus. Author improvement is determination of the inner volume of a sample cell, which was measured using liquid normal butane. Using a new method, the following critical parameters were predetermined. Critical temperature of 304.143 K and density of 466.6 kg/m3 were determined with the expanded uncertainties (k=2) of 0.010 K and 1.1 kg/m3, respectively for carbon dioxide. Critical temperature of 407.808 K and density of 223.0 kg/m3 were determined with the expanded uncertainties (k=2) of 0.0094 K and 1.1 kg/m3, respectively for isobutene.
