Measurements of Mean Heat Transfer Coefficients for Turbulent Forced Convection in a Rectangular Duct With Uniformly Spaced Plate Inserts

An experimental investigation of turbulent forced convection from single and multiple heated plates in the spatially-periodic fully-developed region of air flows in a straight rectangular duct with uniformly spaced plate inserts is described. The focus in this work is on measurements of temporally- and spatially-averaged heat transfer coefficients on the surfaces of the aforementioned plates. The experimental technique is based on a lumped parameter analysis. Six different heated plates were specially designed, constructed, and instrumented for this work. Each of these heated plates was made up of a central metal section (brass, aluminum, or copper) and two plastic end sections (Ertalyte): the metal section was constructed from a top part and a bottom part, with grooves milled in the bottom part to accommodate three thermocouples and an electrical heating wire; the plastic sections were used to reduce the rates of heat loss from the ends to negligible amounts compared to that due to forced convection from the lateral surfaces of the metal section to the air. The Reynolds number used in the presentation of the results is based on the time-mean average streamwise velocity in the minimum cross-sectional area of the duct and a hydraulic diameter: its values ranged from 2,000 to 30,000. Details of the experimental technique used and the results obtained are presented and discussed.