The application of exergy destruction minimization in convective heat transfer optimization

Abstract

An approach of heat transfer enhancement by reducing the irreversibility of process is discussed theoretically. The irreversibility of heat transfer process has been analysed with exergy. The irreversibility of heat transfer process can be expressed with exergy destruction. Other than entropy generation minimization and entransy dissipation minimization, a new approach called exergy destruction minimization is proposed to optimize heat transfer process based on the analysis. By setting exergy destruction rate as an optimization objective and fluid power consumption as a constraint condition, a momentum equation with an additional volume force is constructed through functional variation to numerically simulate convective heat transfer in coupling with energy equation. The approach of exergy destruction minimization is applied in the optimization of convective heat transfer and numerical calculation is carried out to validate this approach in circular tubes. The optimum velocity field with 380% increase in Nu number and 5% increase in flow resistance f is found by the numerical calculation on optimization equations. The results disclose that longitudinal swirl flow with multi-vortexes appears in the flow field, which leads to heat transfer enhancement. The more the vortexes are, the higher Nu number can be gotten. It is found that longitudinal swirl flow with multi-vortexes is a flow pattern with good heat transfer performance in circular tubes. The results of numerical calculation can be used to guide the design for tube inserts.