Convective heat transfer and fluid flow in the inlet region of parallel-plate and corrugated channels

Mir Mosaddeq Ali, Purdue University

Abstract

Experimental and numerical investigations have been performed to determine the heat transfer augmentation for simultaneously developing flow in a corrugated channel, relative to a parallel-plate channel. The range of Reynolds number, Re, for the present study was between 150 and 4000 using water as the working fluid. Two channel spacings were considered with b/L = 0.15 and 0.23, where b is the channel spacing and L is the axial length of one corrugation cycle, for a single corrugation angle of 20$\sp\circ$. Flow visualization studies in the corrugated channel revealed the existence of steady and unsteady spanwise vortices and also suggested the presence of longitudinal vortices. Flow instabilities occurred in both the corrugated channels for Re as low as 500. Average heat transfer enhancement was approximately 125% and 200% in the corrugated channels with b/L = 0.15 and 0.23, respectively. The corresponding increases in the friction factor was approximately 120% and 275%. A performance evaluation under the design criteria of equal mass flow rate, equal pumping power and equal pressure drop per unit length established both the corrugated channels as superior to the parallel-plate channel in intensifying the heat transfer. Limited mixed convection experiments were performed in the larger corrugated channel for two Grashof numbers (Gr) approximately equal to 10$\sp5$ and 5 $\times$ 10$\sp4$ for 100 $<$ Re $<$ 400. The increase in heat transfer was about 25% at Gr = 10$\sp5$ relative to Gr = 5 $\times$ 10$\sp4$. A finite element method, employing isoparametric quadrilaterals, was used to predict the flow and heat transfer characteristics in the corrugated channel numerically for steady state conditions. The numerical results were found to underpredict the heat transfer augmentation achieved in the experiments. This difference is attributed to the presence of longitudinal vortices and unsteadiness in the actual flow that were not revealed by the two dimensional steady state calculations.

Degree

Ph.D.

Advisors

Ramadhyani, Purdue University.

Subject Area

Mechanical engineering

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