Forced-convective internal cooling of a horizontal equilateral-triangle cross-sectioned duct

An experimental determination of the steady-state forced convection from the internal surfaces of a horizontal, uniformly heated electrically, equilateral-triangle cross-sectioned duct with sharp corners has been undertaken. The average Nusselt number Nu_D, using the hydraulic diameter as the characteristic physical dimension, is a constant if the flow in the duct is laminar, but a function of the air's Reynolds number, when the flow is turbulent. Non-dimensional correlations, which can be used for predicting the value of the steady-state rate of convective heat transfer from such a triangular duct into the airflow, have been deduced, viz. Nu_D = 3·25 for laminar flows, i.e. Re_D < 1450; and Nu_D = 0·012 Re_D^0·83 for turbulent flows, i.e. Re_D ≥ 1450.