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PRESSURE DROP AND HEAT TRANSFER IN A MINICHANNEL FLOW SYSTEM INVOLVING TWO STRAIGHT SECTIONS SEPARATED BY A 90° BEND

Patrick H. Oosthuizen
Department of Mechanical and Materials Engineering, Queen's University, 130 Stuart Street, Kingston, ON, K7L 3N6, Canada

Abstract

Incompressible flow through a minichannel (here taken to imply a channel with a size that is of the order of 1 mm with flows that are such that the Reynolds number is between about 1 and 1000) system have been considered in the present study. The channel has a rectangular cross-section. The flow enters the channel with a uniform velocity and passes through a straight channel section that has a length that is 30 times the width of the channel. The flow then passes around a 90° bend. Following the bend, the flow passes down another straight channel which also has a length of 30 times the width of the channel. A uniform heat flux is applied over the entire surface of the duct. The flow geometry does not represent any that is likely to occur in minichannel system applications but is adequate for the evaluation of the assumptions often adopted regarding pressure losses, flow development length and heat transfer rates in real systems. It has been assumed that the flow is steady, that the flow is incompressible, that the velocity and temperature are uniform over the channel inlet plane, and that there is no slip on the channel boundaries. The governing equations have been written in dimensionless form. Solutions to these dimensionless governing equations have obtained using a commercial finite-element software package, FIDAP. The solution has the following parameters: the Reynolds number, Re, the Prandtl number, Pr, the height-to-width ratio of the channel cross-section, H, and the dimensionless radius of the bend Ri = ri/w where w is the width of the channel and ri the radius of the inside surface of the bend. Results are only presented here for Pr = 0.7 and Ri= 1. Re values between 10 and 500 and Hvalues between 0.5 and 2 have been considered. The effect of the governing parameters on the pressure losses, flow development lengths and heat transfer rates has been studied.

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