Comparative Analysis of Equations of State for Calculating the Thermodynamic Properties of a Vapor-Liquid Multicomponent
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COMPARATIVE ANALYSIS OF EQUATIONS OF STATE FOR CALCULATING THE THERMODYNAMIC PROPERTIES OF A VAPOR-LIQUID MULTICOMPONENT REFRIGERANT BLEND COMPRISING THE WORKING FLUID OF A LOW-TEMPERATURE THROTTLING REFRIGERATION UNIT E. G. Bychkov,1 B. A. Makarov,1 V. I. Yakovlev,1 Ya. V. Samokhvalov,1 and A. A. Zherdev2
UDC 621.565.6
The computation methods of the thermodynamic properties are used for theoretical studies of multicomponent refrigerant blends (MRBs) for low-temperature throttling refrigeration units, providing cryostatting modes for cooled objects in the temperature range of –90 – –160 °С. The article presents the comparative analysis of the state equations for calculating thermodynamic properties of multicomponent refrigerant mixtures. Quantitative and qualitative differences in the results of calculations in the lowtemperature region are determined. Keywords: low-temperature refrigeration unit, refrigerant blend, thermodynamic properties, equation of state.
The calculation of the thermodynamic properties of multicomponent refrigerant blends (MRBs) constitutes a fundamental task in the theoretical study of phase transitions in closed-cycle low-temperature throttling refrigerators (LTTRs), on which basis the cryostatting mode is determined. Units for the low-temperature fractionation of hydrocarbons and methane liquefaction were among the first refrigeration units developed on the basis of LTTRs using MRBs of various qualitative compositions. Saturatedhydrocarbon blend variations (such as isobutane, n-butane, propane, ethane, methane, etc.) providing cooling temperatures down to –160 °С were used as the working fluid in such units [1]. Later, V. M. Brodyanskii and his students reasonably proposed nitrogen-based MRBs. These MRBs were developed as the working fluid for microcryogenic systems at the nitrogen cryostatting level. In general, the choice of MRB components is based on differentiating the components by the boiling point. In practice, it is also important to consider the pattern of the blend temperature changes in the process of removing the heat load (following the throttle), which, in turn, depends on the characteristics of the solution formed by the refrigerant blend. For solutions characterized by complete solubility (for example, blends of nitrogen and fluorocarbon refrigerants), the boiling point depends on the concentration of the components, increasing with an increase in the proportion of high-boiling components. For these blends, low temperatures are obtained either by lowering the pressure of the return stream or by introducing a more volatile component into the blend to reduce the partial vapor pressure of the main component. Since return stream pressure reduction involves the risk of air entering the working fluid, as well as requiring an increase in the overall dimensions of the compressor, this approach is not generally used in the design of actual LTTRs. 1 2
Central Scientific Research Institute “Kurs”, Moscow, Russia.
Bauman Moscow State Technical University, Russia; e-mail: BychkovEG@ky
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