Experimental and Computational Investigation of Natural Convection in a Rectangular Duct with Internal Heat Source

Abstract

To design passive air-cooled heat exchangers, an experimental study on natural convection in a square or rectangular duct was felt necessary, as literature on this subject is not available. In the present study, experiments were carried out using a square duct of size 500 × 500 × 800 mm height fabricated with 3.0 mm thick aluminium sheet and a brass cylinder of diameter 25 mm and height 200 mm was used as internal heat source. The heated duct was cooled by natural circulation of air. A 3D Computational Fluid Dynamics (CFD) model for natural convection with variable properties of air and no-slip condition was developed. Laminar simulations of cooling of a vertical cylinder in a rectangular duct was obtained by solving the governing equations using Fluent 6.2.16 along with Gambit v4.6.0 as pre-processor for grid generation. Grid generation resulted in 23,800 cells with 24,185 nodes. Segregated solver solution methodology has been used for simulation with implicit linearization of the Equations (10–14). Finite volume or control volume discretization technique has been used with iterative solution techniques. Residual of the order of for momentum equation, laminar model and for energy equation was used for convergence and stability check. The solver used was based on SIMPLE algorithm. Variation of density and viscosity of air with temperature were accounted for in the simulation. The model was validated by using experimental data. Average heat transfer coefficients were estimated. It was found that the theoretically calculated average heat transfer coefficients were in good agreement with the modelled values.