Plate-spacing effect on unsteady flows and heat transfer characteristics in a channel with inclined plates

Flow and heat transfer characteristics in a channel with inclined plates are investigated numerically. To determine the effect of plate spacing, the ratios of plate pitch to channel height L/H = 1-9; plate angles alpha = 60 degrees, 90 degrees and 120 degrees; and plate lengths d/H = 0.2-0.6 are adopted and unsteady simulations performed. As L/H increases, unsteady flows related to the supercritical Hopf bifurcation are developed and heat transfer characteristics severely changed. Hence, the peculiar relation between plate pitch and vortex evolution is observed. When the plate pitch increases, the observed vortices between the inclined plates can be classified into three patterns, namely, recirculation bubble, standing vortex, and traveling vortex. Unsteady features depending on the plate pitch are also examined by spectral analysis. As the plate pitch increases, the steady state of recirculation bubble is changed gradually to a quasi-periodic state of the traveling vortex through the periodic state of the standing vortex. From these results, the heat transfer enhancement is discussed with vortex evolution, flow oscillation, and law of the wall.