Heat Capacity of Saturated and Compressed Liquid Dimethyl Ether at Temperatures from (132 to 345) K and at Pressures to 35 MPa

Jiangtao Wu, Joseph W. Magee

Index: 10.1021/acs.jced.8b00037

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Abstract

Molar heat capacities at constant volume (Cv) of dimethyl ether have been measured with an adiabatic calorimeter. Temperatures range from the triple point to 345 K, and pressures up to 35 MPa. Measurements were conducted on liquid in equilibrium with its vapor and on compressed liquid samples. The samples are of high purity, as verified by chemical analysis. Calorimetric quantities are reported for the two-phase (Cv(2)), saturated-liquid (Cσ or Cx′), and single-phase (Cv) molar heat capacities. Low temperature Cv(2) data were employed to estimate vapor pressures for values less than 340 kPa by applying a thermodynamic relationship between the two-phase internal energy U(2) and the temperature derivatives of the vapor pressure. Vapor pressures were calculated at temperatures as low as the triple-point temperature. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k = 2 and thus a two-standard deviation estimate) is estimated to be 0.7% for Cv, 0.5% for Cv(2), and 0.7% for Cσ.