A CONSTANT VOLUME APPARATUS FOR VAPOR-PRESSURE AND GAS-PHASE P-V-T MEASUREMENTS - VALIDATION WITH DATA FOR R22 AND R134A

We describe a constant volume apparatus using a spherical cell for the experimental determination of vapour pressure and gas phase pressure-volume-temperature (P-v-T) data for alternative refrigerants. This apparatus has been designed for measurements in the temperature range from 245 K to 365 K and for pressures up to 5 MPa. The modifications done to the existing apparatus and the experimental procedure employed to improve the quality of data are explained in detail. The uncertainties involved in the measurement of temperature, pressure, mass and volume are also discussed. New measured data for vapour pressure and P-v-T behaviour in gaseous state for high purity samples of chlorodifluoromethane (R22) and 1,1,1,2-tetrafluoroethane (R134a) and the validation of the experimental procedure are presented. The validation has been performed by comparing the measured data with correlations and data available in recent literature in terms of the following statistical parameters: percentage deviation, absolute average deviation, bias, standard deviation, root mean square deviation and the difference in pressure. The results indicate that the constant volume cell with measuring instruments and the procedure employed gives reliable and accurate data.