Study on the Vapor-Liquid Equilibria using a Composition Analysis Technique from Ultrasonic speed for Hydrofluorocarbon Mixtures.

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The vapor-liquid equilibria for fluid mixture is important thermodynamic properties to measure the characteristics of system and to design the process. The studies on the vapor-liquid equilibria for several mixtures have been reported elsewhere. The composition of systems in these studies has been observed by analyzing on the gas clomatogram. However, this technique was very difficult to measure the vapor-liquid equilibria at very lower or higher temperatures than the room temperature. Because the different of conditions (pressure and/or temperature) between the sample chamber and the injection of gas-chlomatograph give rise to irregularity to the composition determination for systems, especially in the cases of those having higher bubble or dew points pressures.The ultrasonic speeds in fluid can be measured accurately at critical conditions. In the previous works. Takagi reported the vapor pressure and bubble point pressure for same hydrofluorocarbons measured by an acoustic absorptio … More n technique in the wide temperature ranges. In this work. the new apparatus for measurement the vapor-liquid equilibria was constructed. The method used here was the composition analysis technique from the ultrasonic speed in the hydrofluorocarbon mixtures. In the high pressure equilibrium cell made stainless steel, SUS3 16, two chambers to measure the ultrasonic speed in gas (upper side) and liquid (lower side) phases were set up in parallel. Also this vessel have two optical windows to observe the condition of cell inside.In order to confirm the reliability of new apparatus, the VLE for (1-x)HFC32 + x HFCI34a. which have the large difference in the vapor pressures between both pure substances. were measured at several temperatures. from 243.15 to 333.15 K, and compositions. x. The uncertainties of VLE obtained are within 2.5% for the bubble point pressure and 7% for the dew point pressure by comparison with the references data. For (1-x) HFC32 + x HFC 125, the vapor pressure difference between the pure substances was small. the VLE were also measured at same conditions described above. The experimental errors for this system. which have an azeotrope. were a larger than those for former system, especially for dew point pressure. Less