Specific Heat Capacity at Constant Volume for Water, Methanol, and Their Mixtures at Temperatures from 300 K to 400 K and Pressures to 20 MPa

Specific heat capacities at constant volume (c v) of water, methanol, and their mixtures were measured with a new adiabatic calorimeter. Temperatures ranged from 300 K to 400 K, and pressures ranged to 20 MPa. Densities were determined at the initial and final end points during each calorimetric experiment. The calorimeter is a twin-cell type whose sample and reference cells (33 cm3) and their shields are heated by electric power. The cells are surrounded by a high vacuum. During the experiment, the heating power was carefully controlled so that the cell temperature increased uniformly. The reference cell was always evacuated and was heated with a constant current. The temperature of the sample cell tracked that of the reference cell temperature by means an automatic control system. Automated sample pressure measurements were made with a crystal quartz transducer. The expanded relative uncertainty for c v is estimated to be 1% for liquid-phase measurements, and for density it is about 0.2%.