High-Pressure Isochoric Apparatus and Technique for Accurate Phase Loop Determinations: The Bubble Point Region

We present our new high-pressure isochoric apparatus for phase loop determinations at Texas A&M University. We start at high pressures in the cell (up to 200MPa), come down as isochores, and hit low temperature bubble points when entering the two phase region. This apparatus has a high-pressure cell made of Be-Cu, coarse and fine heat transfer, automatic temperature monitoring and control, and pressure measurement systems. The accuracies of the sensors are ±2mK for the platinum resistance thermometer and 0.01% full scale for the Paroscientific pressure transducer. Calibration and testing procedures use carbon dioxide and methane. We present an improved statistical treatment for phase loop determinations using the isochoric technique. It has produced maximum uncertainties, usually in the proximity of the cricondentherm, of 0.45% in temperature and 0.04% in pressure for phase boundaries of multicomponent mixtures (up to 22 components) taken with the low-pressure isochoric apparatus.