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Chapter 8: Modeling Radiation and Natural Convection

This tutorial is divided into the following sections:

8.1.Introduction

8.2.Prerequisites

8.3.Problem Description

8.4.Setup and Solution

8.5.Summary

8.6.Further Improvements

8.1. Introduction

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.

8.2. Prerequisites

This tutorial is written with the assumption that you have completed one or more of the introductory tutorial Fluid Flow and Heat Transfer in a Mixing Elbow (p. 35) found in this manual and that you are familiar with the ANSYS Fluent tree and ribbon structure. Some steps in the setup and solution procedure will not be shown explicitly.

8.3. Problem Description

The problem to be considered is shown schematically in Figure 8.1: Schematic of the Problem (p. 278). A three-dimensional box has a hot wall of aluminum at 473.15 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 293.15 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.

The working fluid has a Prandtl number of approximately 0.71, and the Rayleigh number based on

(0.25) is . This means the flow is most likely laminar. The Planck number is 0.006, and measures the relative importance of conduction to radiation.

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