Construction of Polynomials for Calculating the Thermophysical Properties of Low-Boiling Working Substances

Information technologies in the form of integrated electronic reference books and polynomials for determining the properties of working substances are widely used in engineering calculations and in the design of large-scale energy facilities. However, for a large number of small-scale energy projects, the interest in which increases from year to year, the use of non-traditional working substances is proposed. The analysis of the effectiveness of using such substances as working bodies of power plants, as well as the constructive elaboration of the elements of the thermal circuit, is significantly complicated by the need to repeatedly refer to reference books in “manual” mode, since modules for calculating thermophysical properties are often not integrated into modern computing programs. This paper presents a method for constructing polynomials of thermophysical properties of low-boiling working substances in the Wolfram Mathematica program. A step-by-step approbation of the proposed technique has been performed and approximation dependencies have been developed for calculating the properties of pentane in the single-phase region and on the saturation curve in the specified parameter ranges. The type (mathematical form) of polynomials for each of the considered areas of pentane properties is proposed. The properties were calculated based on the obtained dependencies and compared with the original data array. The calculated data on the properties of pentane by polynomials showed a good match with the initial reference data in a given range of parameters. All points of the algorithm for constructing polynomials are illustrated with screenshots of the program for ease of use of the technique.