Entropy generation and exergy efficiency in adiabatic mixing of nitrogen and oxygen streams of different temperatures and environmental pressures

Abstract

The paper presents a non-dimensional model of entropy generation and exergy efficiency in the adiabatic mixing of a nitrogen stream and oxygen stream with different temperatures and environmental pressure. The resulting mixture has the same, i.e. environmental, pressure. Non-dimensional variables in the model represent the ratio of thermodynamic stream temperatures u, the ratio between the thermodynamic temperature of one stream and the environmental temperature u1, and the mole fraction y1 of one of the streams. The model comprises irreversibility due to different temperatures of streams because of the mixing of different gases, while exergies of streams also comprise their mole fractions in the ambient air (atmosphere). In this respect, the model takes the standard values of mole fractions of oxygen and nitrogen of yO2 = 0.21 and yN2 = 0.79. The values of stream mole fractions at which maximum values of entropy generation and minimum values of exergy efficiencies occur are given. Calculation results are given in respective diagrams.