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# Modeling Radiation and Natural Convection

Many techniques have been introduced in the past years to improve the efficiency of heat exchange systems involving natural convection and/or forced convection, and with or without phase change. In this area of research, researchers have considered heat transfer enhancement in natural convection using an array of discrete plate segments in lieu of a continuous uninterrupted surface. Their study was aimed at reducing the thermal boundary layer thickness in order to obtain higher heat transfer coefficients.

In this tutorial, combined radiation and natural convection are solved in a three-dimensional square box on a mesh consisting of hexahedral elements.

This tutorial demonstrates how to do the following:

• Use the surface-to-surface (S2S) radiation model in ANSYS FLUENT
• Set the boundary conditions for a heat transfer problem involving natural convection and radiation
• Calculate a solution using the pressure-based solver
• Display velocity vectors and contours of wall temperature, surface cluster ID, and radiation heat flux

### Problem Description

The problem to be considered is shown schematically in picture below. A 3D box (0.25m x 0.25m x 0.25m) has a hot wall of aluminum at 473 K. All other walls are made of an insulation material and are subject to radiative and convective heat transfer to the surroundings which are at 293 K. Gravity acts downwards. The medium contained in the box is assumed not to emit, absorb, or scatter radiation. All walls are gray. The objective is to compute the flow and temperature patterns in the box, as well as the wall heat flux, using the surface-to-surface (S2S) model available in ANSYS FLUENT.