Thermal and Flow Analysis of Air in a Uniformly Heated Circular Channel with an Inlet Flap Obstruction in Laminar, Transitional, and Turbulent Flow Regimes

Abstract

An experimental investigation has been carried out to study the thermohydraulic performance of air in transitional flow regime in a circular uniformly heated channel fitted with flap obstruction at the inlet. The Reynolds number (Re) varied from 500 to 7,037. The channel is uniformly heated using heat fluxes of 0.5 and 1 kW/m2. Three height and width ratios were used as variable parameters. Correlations for predicting the Nusselt number and friction factor were developed. It was found that for a uniformly heated (1 kW/m2) plain channel, the critical Re for the start of transition is 2,752, and the critical Re for transition termination is 3,667. It was also found that placing the flap obstruction at the inlet of the test section results in early start and end of the laminar-turbulent transition. At heat flux of 0.5 kW/m2, the transition begins as early as Re = 1,840 and ends at Re = 3,588, and similarly, for a heat flux of 1 kW/m2, the transition begins at Re = 1,859 and ends at Re = 3,604. The highest Nusselt number enhancement was reported for hight ratio of 0.75 and width ratio of 0.25 and for a heat flux of 1 kW/m2.