利用乙醇音速计算其它热力学性质

The valid temperature range of the light scattering method used to measure the speed of sound is particularly wide. Besides, the specific heat capacity at constant pressure is easier to measure compared with density sometimes. Under these circumstances, an iterative algorithm was proposed to calculate the density at high temperatures from the specific heat capacity at constant pressure at high temperatures. Taking ethanol as an example, the densities of ethanol at 298.15∼418.15 K and 1.0 MPa were calculated by using the prediction model, and were compared with the calculated results of Schroeder's equation of state, which results in the average absolute relative deviation of 0.0119% and the maximum deviation of 0.0298%. In addition, the speeds of sound in liquid ethanol over the temperature range of 298.45∼423.02 K were measured along 1.0 MPa isobars with an extended relative uncertainty of 0.9% (confidence factor is 2). Compared with Schroeder's equation of state, the average relative deviations of the calculated density and calculated specific heat capacity at constant pressure of ethanol at 298.15∼418.15 K and 1.0∼9.0 MPa were 0.0072% and 0.0067%, respectively, and the maximum deviations were 0.0298% and 0.0290%, respectively. It can be seen that the calculation accuracy of the prediction model for calculating thermodynamic properties at high temperatures is equivalent to the experimental measurement accuracy.