Keywords: engineering thermodynamics, basic exergy definitions, gravity potential exergy, exergy balance, exergy analysis, air expansion, turbines, air throttling, compression
Gravity influence on the exergy balance
New component of 'mechanical exergy' of substance, proposed earlier by Petela, is based on the difference of densities of the substance and the atmosphere. Application of this component does not fulfil the traditional exergy balance equation. Thus, additional equation term, called 'gravity input', is proposed here. The term, expresses the effect of gravity field on the considered process and is positive, negative or zero. The gravity input allows for widening of interpretation of exergetic analysis. Two exemplary processes are analysed: air expansion in turbine and air throttling followed by compression. The results from the new and traditional exergy balance are compared.