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Experimental Densities, Vapor Pressures, and Critical Point, and a Fundamental Equation of State for Dimethyl Ether



E. Christian Ihmels, Eric Lemmon


Densities, vapor pressures, and the critical point were measured for dimethyl ether, thus filling several gaps in the thermodynamic data for this compound. Densities were measured with a computer-controlled high temperature, high-pressure vibrating-tube densimeter system in the sub- and supercritical states. The densities were measured at temperatures from 273 to 523 K and pressures up to 40 MPa (417 data points), for which densities between 62 and 745 kg/m3 were covered. The uncertainty in density measurement was estimated to be better than 0.1 % in the liquid and compressed supercritical states. Near the critical temperature and pressure, the uncertainty increases to a maximum of 1 %. Using a variable volume apparatus with a sapphire tube, vapor pressures and critical data were determined. Vapor pressures were measured between 265 K and 200 kPa up to near the critical point with an uncertainty of ? 0.1 kPa. The critical point was determined visually with an uncertainty of 1 % for the critical volume, 0.1 K for the critical temperature, and 5 kPa for the critical pressure. The new vapor pressures and compressed liquid densities were correlated with the simple TRIDEN model. The new data along with the available literature data were used to develop a first fundamental Helmholtz equation of state for dimethyl ether, valid from 131.65 to 525 K and for pressures up to 40 MPa. The uncertainty in density of the equation of state ranges from 0.1 % in the liquid to 1 % near the critical point. The uncertainty in heat capacities is 5 %, and the uncertainty in vapor pressure is 0.25 % at temperatures above 200 K. Although the equation presented here is an interim equation, it represents the best currently available.
Fluid Phase Equilibria


critical point, density, dimethyl ether, equation of state, vapor pressure


Ihmels, E. and Lemmon, E. (2007), Experimental Densities, Vapor Pressures, and Critical Point, and a Fundamental Equation of State for Dimethyl Ether, Fluid Phase Equilibria, [online], (Accessed May 26, 2024)


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Created January 21, 2007, Updated October 12, 2021