Combined flow-mixing power-compensation calorimeter and vibrating tube densimeter for measurements at superambient condition

A new instrument combining a flow-mixing calorimeter and a vibrating tube d ensimeter inside a thermostatted environment has been constructed. The inst rument is designed for simultaneous measurements of calorimetric and volume tric properties at superambient conditions on mixtures for which both pure components are liquid at room temperature or one component is a liquid and the other is gaseous. The system yields simultaneously two properties: (1) the enthalpy of mixing determined in a heat-leak calorimeter with power com pensation; (2) the density difference between a mixture (solution) and a re ference liquid measured as a change in frequency of a tube vibrating in a f ield of permanent magnets. The instrument was tested in the full concentrat ion range using aqueous ethanol and aqueous methanol. The results are prese nted at temperatures between 348 and 573 K and pressures from 5 to 20 MPa f or mixing enthalpies Delta H-mix ranging from -160 to 5700 J-mol(-1). The c orresponding heating powers are between -60 and 850 mW, respectively. The r esults for Delta V-mix of mixing volumes were measurable from 348 K to 523 and between 5 and 13 MPa with the maximum volume change being -4.0 cm(3)-mo l(-1). The errors in Delta H-mix and Delta V-mix near mole fraction of 0.5 are believed to be less than 5% over the temperature and pressure ranges gi ven above.