Forced turbulent air flow with heat convection in a square duct

A model is presented for solving the system of turbulentforced heat convection in a horizontal square duct with fullydeveloped velocity distribution and developing temperatures.Air is the only fluid considered.Similar algebraic expressionsfor turbulent viscosity and conductivity were assigned in each ofthree layers into which the duct cross-section was dividedThisimplies considerable similarity between the velocity and temperaturefields.Two sets of thermal boundary condition~ were imposed onthe duct walls.Firstly, the ,two vertical duct sides areisothermal and the horizontal ones adiabatic, while secondly, allsides are isothermal.The numerical solution was carried out by the finite elementmethod based on the Galerkin proFess.Triangular elements wereused in solving the momentum equation, and tetrahedral elements inthe case of the energy equation.The computer program wasconstructed to enable calculation for any duct length withoutincreasing the computer capacity needed, and with adequate accuracy.Another program obtained the system parameters at any cross-section,by means of the Simpson method.An experimental rig was constructed in accordance with the’above system, providing a velocity development length, and twoisothermal and two adiabatic walls in the heating section.Wallshear velocity, axial velocity, and temperature were measured atthe duct exit.These data guided the choice’ of values of all themodel assignable constants.WThe solution was determined for constant,~briefly, forvariable fluid properties.Two alternative techniques for the