Technical Papers and Presentations

Numerical study of fluid flow and heat transfer in a finite three-dimensional rectangular, horizontal duct of length to width, and length to height ratio of 12:1 is investigated in this study. The left wall of the duct is uniformly heated while the right, top, and bottom walls are adiabatic. Air of uniform velocity and temperature is assumed to enter the duct. The finite element method approach is employed to solve the dimensionless continuity, Navier-Stokes and energy equations simultaneously with the COMSOL Multiphysics^® simulation software. Results are computed for different flow scenarios with low ranges of Re and Ri numbers; also, the cases of opposed and assisted convection are studied. The effects of the increase in Re and Ri numbers specifically on reverse flow are investigated. Plots of the dimensionless heat transfer parameter Nu/Re^0.4 against the dimensionless length scale are also generated for each rectangular plane in the 3-D geometry to understand the effect of the mixed convection flow on heat transfer.

In this work, the CFD and the Heat Transfer modules of COMSOL Multiphysics^® were very effective. First, the COMSOL Multiphysics^® software was opened then Model Wizard >> 3D >> Fluid Flow >> Nonisothermal flow >> Laminar flow >> General Studies >> Stationary were selected in that order to set-up the problem to be solved. The geometry was built using an inbuilt block function and dimensioned appropriately. Under the materials node, the whole block was selected and set to air. The velocity and the heat flux value for each flow scenario was calculated manually using the Re and Ri (Gr/Re²) numbers.

In the Laminar Flow physics, the walls, front, back, left, and right, were set to no-slip wall by default and incompressible flow was selected; the “include gravity” and “reduced pressure” checkboxes were checked to account for gravity and Boussinesq approximation. The inlet and outlet boundaries were selected appropriately. In the heat transfer in fluids component, the reference temperature was set to 273.15 K, the room temperature. Heat flux boundary was selected and the left wall was chosen. The general inward heat flux was selected and assigned the calculated heat flux value. Under the multiphysics component and under the Nonisothermal flow node, the whole block was selected and the Boussinesq approximation checkbox was checked. The outflow and inflow were selected for each flow scenario appropriately. The meshing technique and convergence criteria in the FEA method are varied for both assisted and opposed convection to obtain the best grid-independent results. Under the Meshes component and under mesh node, user-controlled mesh was selected and other appropriate boundary meshes were selected for the block.

The generated heat transfer averaged results in the form of Nusselt number plots as functions of the various geometric and flow parameters are compared with limited published work in the literature. Comparison shows good agreement. Results obtained in this work compare well with those in literature.