SECOND-LAW ANALYSIS OF HEAT TRANSFER ENHANCEMENT IN OFFSET-STRIP-FIN COMPACT HEAT EXCHANGERS
The second law of thermodynamics has been applied to evaluate the heat transfer enhancement of offset-strip-fin cores relative to plain plate-fin compact heat exchangers. Single-phase air flows, in both laminar and turbulent regimes are considered. The thermal-hydraulic performance in terms of the area goodness factor, jlf, and entropy generation number, Nsa, is presented. Recognizing that the irreversibility reduction is a trade-off between heat transfer enhancement and the corresponding pressure drop penalty, a new parameter, entropy generation distribution factor, ψ, is proposed. It is a ratio of entropy reduction due to improved heat transfer and the increased irreversibility due to friction loss; ψ > 1 implies net thermodynamic benefits. The magnitude of ψ is such that a better resolution is obtained for the change in entropy generation due to variations in operating conditions. The relative influence of the aspect ratio, α, fin density, γ, and fin-thickness-to-offset-length ratio, δ, of offset-strip fins on heat transfer enhancement and minimization of entropy generation is delineated.