A computational study of enhanced heat transfer in laminar flows of Newtonian and non-Newtonian (power-law and Herschel-Bulkley) fluids in corrugated-plate channels.

摘要

Single-phase periodically developed, constant property, laminar forced convection in sinusoidal corrugated-plate channels with uniform wall temperature is considered. Newtonian, power-law non-Newtonian, and Herschel-Bulkley fluids are considered in the current dissertation work. Numerical solutions are obtained using the control-volume method and the commercial code FLUENT.; For the Newtonian fluids, a wide range of channel corrugation aspect ratio (0 ≤ γ ≤ 1), different flow rates (10 ≤ Re ≤ 2000) of viscous liquids (Pr = 5, 35, and 150) are considered. The flow field is found to be strongly influenced by the corrugation aspect ratio, γ, and it displays two distinct regimes: undisturbed laminar or no swirl, and swirl flow regimes. In the no-swirl regime, the flow behavior is very similar to that in fully developed straight duct with no cross-stream disturbance. In the swirl regime, flow separation and reattachment in the corrugation troughs generates transverse vortex cells that grow with Re and γ, the transition to this regime also depends on Re and γ. The mixing produced by these self-sustained transverse vortices is found to enhance the heat transfer by up to thirty four times that in a flat parallel-plate channel, depending upon γ, Re, and Pr. The corresponding friction factor, however, is only seventeen times higher.; Similarly, for the power-law non-Newtonian fluids a wide range of channel corrugation aspect ratio (0 ≤ γ ≤ 1), flow rates (10 ≤ Re _g ≤ 1500), and pseudoplastic flow behavior indices (n = 0.5, 0.8, and 1.0) are considered. Typical velocity and temperature distributions, along with extended results for isothermal friction factor f and Collburn factor j are presented. The enhanced forced convection is found to be strongly influenced by the corrugation aspect ratio γ, and the flow field displays two distinct regimes: undisturbed laminar or no swirl, and swirl flow regimes. In the no-swirl regime, behavior similar to that in fully developed straight duct flows with no cross-stream disturbance is obtained. The shear-thinning nature of the fluid, however, decreases f and enhances j. In the swirl regime, flow separation and reattachment in the corrugation troughs generates transverse vortices that grow with Re_g and γ. (Abstract shortened by UMI.)