Developing forced convection in converging-diverging microchannels

In this paper, the effects of geometrical configuration on heat transfer performance and fluid flow of converging-diverging microchannels are studied numerically. Geometrical parameters are presented in nondimensionalized format, i.e., aspect ratio, S, waviness, λ, and expansion factor, γ. For five different aspect ratios and different levels of wall curvature, Nu and f are determined for three Re, i.e., 200, 400 and 600. Different mechanisms that affect the performance of the microchannel design are addressed and at each level of waviness, dominancy of each mechanism is discussed. Flow structures formed are studied and counter rotating vortices created in the trough region are found to have an adverse effect on heat transfer. At highly pronounced levels of wall curvature, chaotic advection is observed which results in higher heat transfer rates albeit with higher pressure penalties. Thus, converging-diverging design is introduced as a planar design with which chaotic advection may be achieved. A Performance Factor (PF) is proposed to capture heat transfer and pumping power characteristics of converging-diverging microchannels by comparing the wavy designs with their corresponding straight configurations. Based on the performance factor introduced, it is observed that the superiority of converging-diverging design shows itself at higher Re for which higher performance of up to 20% is observed.