Second Law Analysis in Assessing Constant Power Input Systems

A criterion for comparing the relative performance of various heat transfer augmentation methods used in constant power input systems is introduced. The analysis is based on the principle of minimizing the rate of total entropy generation. The heat transfer load (HTL), a parameter determined by the operating requirements of the heat dissipating process that indicates the difficulty of the heat transfer duty to be performed, is defined in the present study. By comparing the irreversibility distribution ratio (φ) of various configurations at a given heat transfer load, the most exergy efficient system can be selected. The data for three different types of fin configurations used in two constant power input applications (electronic equipment and internal turbine blade cooling) are utilized in demonstrating the technique. The results indicate which specific fin geometry of the particular configuration type analyzed will transfer the dissipated heat at the specified base surface temperature while requiring the least pumping power. Although the φ versus HTL criterion is applied to only fins in this study, the method can be extended to many other applications such as jet impingement cooling or mass transfer.