NEW DETECTION METHOD FOR DETERMINING PHASE BOUNDARIES

Modifications in the electronics and experimental set-up of the vibrating tube densimeter (Wood et al., 1989. Rev. Scientific Instruments, 60(3): 493-494) allowed the development of a new detection method for determining phase transitions. The method uses the sharp drop in the amplitude of vibration of a vibrating tube when phase separation occurs. The new detector should be especially useful at high temperatures and pressures where other methods are more difficult to use. Combining phase equilibria detection with conventional density measurements allows the vibrating tube to be used to explore P, V, T, and x at phase boundaries. The experimental procedure and set up are presented together with results from measurements of the vapor pressure of both water and aqueous NaCl solutions. The reliability and estimated accuracy of this method for determining vapor pressure is about +/- 0.4%.