Enhanced heat transfer characteristics of low Reynolds number airflows in three-dimensional sinusoidal wavy plate-fin channels are investigated. For the computational simulation, steady state, constant property, periodically developed, laminar forced convection is considered with the channel surface at the uniform heat flux condition; the wavy-fin is modeled by its two asymptotic limits of 100% and zero fin efficiency. The governing equations are solved numerically using finite-volume techniques for a non-orthogonal, non-staggered grid. Computational results for velocity and temperature distribution, isothermal Fanning friction factor f and Colburn factor j are presented for airflow rates in the range of 10 ≤ Re ≤ 1500. The numerical results are further compared with experimental data, with excellent agreement, for two different wavy-fin geometries. The influence of fin density on the flow behavior and the enhanced convection heat transfer are highlighted. Depending on the flow rate, a complex flow structure is observed, which is characterized by the generation, spatial growth and dissipation of vortices in the trough region of the wavy channel. The thermal boundary layers on the fin surface are periodically disrupted, resulting in high local heat fluxes. The overall heat transfer performance is improved considerably, compared to the straight channel with the same cross-section, with a relatively smaller increase in the associated pressure drop penalty.
Enhanced forced-convective heat transfer behavior of air flows (Pr ~ 0.7) in a compact heat exchanger with three-dimensional, sinusoidal-wavy-plate fins is investigated both experimentally and computationally. Plate-fins with three different corrugation aspect ratio γ = (2A/L) = 0.0667, 0.1333, and 0.2667 are explored. Experimental j and f measurements are presented for flow rates in the range 500 < Re < 5000. Computational results, based on control-volume techniques, are obtained for periodically-fully-developed flows with 10 ≤ Re ≤ 1000. The numerically simulated local temperature and flow field map shows the complex influence of corrugation aspect-ratio γ, and the concomitant j and f predictions are in good agreement with experimental measurements. Both j and f increase with γ to reflect the relatively stronger flow recirculation in the wall-trough regions, and spatially more frequent periodic boundary-layer disruptions upstream of the corrugation peaks that enhance heat transfer in plate-fin channels. The relative enhancement, as measured by the Area Goodness Factor (j/f), however is found to be highest with γ = 0.0667.
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