Study of Isochoric Specific Heat Capacity Measurements for Liquid Water-Methanol Mixtures

Published

November 20, 2001

Author(s)

Hiroshi Kitajima, Hiroyuki Miyamoto, Noboru Kagawa, Joe W. Magee, Harumi Endo, Seizo Tsuruno, Koichi Watanabe

Abstract

Hydrogen bonding of water (H₂O) is certain to introduce an effect of the molecular energy to the heat capacity. Due to the presence of the strong hydrogen bonding, interactions between water and methanol (CH₃OH) molecules show anomalous thermodynamic properties. Measurements of thermodynamic properties are essential to characterize such interactions and to model this behavior with an equation of state. Specific heat capacity at constant volume (C_v) is one of the most important thermodynamic properties to develop and evaluate thermodynamic properties equations of state. With this point of view, C_v) values of water, methanol and their mixtures were measured with an adiabatic calorimeter developed at the NDA. After those early measurements, some modifications were carried out to improve the performance of the apparatus. This paper reports new measurements made after the modifications. The calorimeter is a twin-cell type whose sample and reference cells (33cm³) and their shields were heated by electric power. The cells were surrounded by 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. Absolute temperatures were measured with a platinum resistance thermometer (PRT) on the bottom of each cell and were reported on the ITS-90. The measurement and temperature-control tasks were executed every 30 seconds. During the interval, the cell temperature increased by about 35 mK. The experimental uncertainty of temperature measurements is plus or minus} 40 mK, and that of pressure measurements is plus or minus} 7 kPa. The expanded relative uncertainty for c_v is estimated to be 1% for liquid phase measurements, and for density it is about 0.2%. Blank test data for the empty calorimeter, required to eliminate the unsymmetrical effect of the cells and the measuring lines, were obtained by heating the evacuated cells. Blank tests covering a temperature range from 280 to 420 K were repeated before each measurement series. As shown in Figures 2 and 3, the new measurements of c_v and density for H₂O and CH₃OH were carefully compared with published equations of state. The low relative deviations shown in the figures support a conclusion that the performance of the apparatus was improved by the modifications.

Proceedings Title

Proc. Japan Symp. on Thermophysical Properties

Conference Location

Sendai, 1, JA

Conference Title

Japan Symp. on Thermophysical Properties

Pub Type

Conferences

Citation

Kitajima, H. , Miyamoto, H. , Kagawa, N. , Magee, J. , Endo, H. , Tsuruno, S. and Watanabe, K. (2001), Study of Isochoric Specific Heat Capacity Measurements for Liquid Water-Methanol Mixtures, Proc. Japan Symp. on Thermophysical Properties, Sendai, 1, JA (Accessed June 30, 2024)