Developing equations for ideal gas air properties

ABSTRACT: The equations for property data of air as an ideal gas are developed. The equations are presented as a function of temperature. Although there are several software capable of using property tables for example, EES, VisSim and etc., others require equations for property calculations such as FORTRAN. Equations are developed by using the ―CurveFitting Expert‖ software. Equations are presented for air properties as a function of temperature are; enthalpy, internal energy, entropy, reduced pressure and reduced volume. Many equations were developed but only those which have high correlations are presented (i.e., equations with highest R2). Moreover, the percent deviations of the calculated properties were studied and the equations which have more than one percent deviation from the tabulated data were neglected. Two equations to calculate temperature as a function of reduced pressure and enthalpy are also presented. The property equations developed in this study were used to simulate a 320 hp actual gas power turbine engine of a small military ship with reheater and recuperator. EES, MATLAB software and the developed equations were used to calculate various properties and the efficiency of the cycle. The difference in the final result (i.e., thermal efficiency) obtained by using the developed equations compared with the result obtained by using the EES software was around 0.1 % which indicated that the developed equations are accurate. Keywords: Curve fitting, air properties, ship propulsion, EES software. …………………………………………………………………………………………………………………………………………………………………………………………………………