A simple model for thermodynamic properties of air and combustion gases for educational purposes

Abstract

A new, simple model for the thermodynamic properties of dry air and combustion gases is presented. The model has been developed mainly for educational purposes with the focus on gas turbine cycle calculations included in university courses. The equations used are short and easy to include in a student computer program. This ideal gas model is based on well-known correlations from the open literature and each equation is an approximated fit to an appropriate expression from the original reference. In the new concept, each relation is expressed using a simple algebraic formulation that has an explicit inverse function. Therefore, the numerical result of an inverse function can be obtained directly, without the involvement of any iterative procedure. This simplifies the programming of auxiliary subroutines for thermodynamic properties. It becomes an easy task and the use of complicated models, in basic university courses, is avoided. Long and complex subroutines which are treated as "black boxes" are now excluded from the code, and a program for thermodynamic cycle calculation is then completely written by a student, starting from the very beginning.