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International Heat Transfer Conference 10

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

SECOND-LAW ANALYSIS OF HEAT TRANSFER ENHANCEMENT IN OFFSET-STRIP-FIN COMPACT HEAT EXCHANGERS

Raj M. Manglik
Thermal-Fluids and Thermal Processing Laboratory, Mechanical and Materials Engineering, University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45220, USA

P. P. Fang
Department of Mechanical, Industrial and Nuclear Engineering University of Cincinnati, Cincinnati, Ohio 45221-0072, USA

DOI: 10.1615/IHTC10.2330
pages 67-72

Résumé

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.

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