Effect of inlet flap obstruction on thermohydraulic characteristics in a smooth circular tube in the transitional flow regime

Abstract

Heat transfer and pressure drop in a uniformly heated circular tube with a flap obstruction in the transitional flow regime is studied experimentally. Air (Pr = 0.707) is taken as the working medium. The Reynolds number (Re) is varied from 500 to 7037. Two heat flux conditions, 0.5 kW/m2 and 1 kW/m2, are considered. The height ratio (h) is varied from 0.15-0.25 and the width ratio (w) is varied from 0.25-0.75. Early onset of laminar to turbulent transition is noticed when flap obstruction is placed at the inlet. The earliest onset of transition is Re = 1918 and the latest is at Re = 3800 for the case of h=0.25 and w=0.25 and 0.5 kW/m2. The transition length for a heat flux of 0.5 kW/m2 case is more than twice the length for a plain channel. At higher heat fluxes, transition begins earlier. The presence of a flap obstruction disturbs the boundary layer resulting in early beginning of transition.