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Study of Isochoric Specific Heat Capacity Measurements for Liquid Isobutane

Published

Author(s)

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

Abstract

Isobutane is one of the most promising alternative refrigerants because of its zero ODP and negligible GWP. It can be used not only as a pure component but also as a component of binary or ternary mixture refrigerants. To design and evaluate cycle performance using these refrigerants, reliable equations of state are required. Although accurate thermodynamic property information is essential to develop and equation of state, available experimental data is limited, especially caloric information in the liquid phase. To better understand isochoric heat capacity behavior in a wider temperature range for liquid isobutane, it would be useful to examine properties derived from its equation of state. Figure 1 shows a twin-cell type adiabatic calorimeter that has been developed by Kuroki et al. In figure 1, a sample cell (K1) was filled with liquid isobutane (99.99 mol% purity) and a reference cell (K2) was always evacuated. The cells were separately placed inside adiabatic shields whose temperatures were controlled to maintain their thermal equilibrium by using sixteen thermocouple and four heaters. Also, the cells were surrounded by high vacuum to improve the adiabatic situation. During a measurement, and electric heater attached to the reference cell was heated with a constant current, and the heating power of another heater attached to the sample cell was carefully controlled so that the temperature difference between the cells was maintained within plus or minus} 5 mK. Each cell temperature was measured with a platinum resistance thermometer and was reported on the ITS-90. The pressure in the sample cell was measured with a quartz crystal transducer. The controls and measurements of the heater electric powers, temperatures, and pressures were automatically executed by a personal computer. The experimental isochoric specific heat capacities were then obtained by adopting Eqs. (1) – (3). The expanded uncertainties (with a coverage factor, K=2) of the present experimental data are estimated to be plus or minus} 36 mK for the temperature, plus or minus} 0.03 % for the pressure, and plus or minus} 2.2 % for the isochoric heat capacity in the liquid. By using the calorimeter, the isochoric specific heat capacity behavior of liquid isobutane was determined in a range of temperatures 227 K ¿ 417 K and pressures 3 MPa ¿ 29 MPa (Figure 3). Figure 4 shows comparisons of the 119 points experimental data with calculations from a Helmholtz-type equation of state developed by Miyamoto and Watanabe. From the comparisons, it is clear that the equation represents the present experimental data adequately.
Proceedings Title
Proc. Japan Symp. on Thermophysical Properties
Conference Dates
November 20-22, 2001
Conference Location
Sendai, 1, JA
Conference Title
Japan Symp. on Thermophysical Properties

Citation

Miyamoto, H. , Kitajima, H. , Kagawa, N. , Magee, J. , Tsuruno, S. and Watanabe, K. (2021), Study of Isochoric Specific Heat Capacity Measurements for Liquid Isobutane, Proc. Japan Symp. on Thermophysical Properties, Sendai, 1, JA (Accessed May 18, 2022)
Created October 12, 2021