Last Updated: 4/30/2019

Radiation View Factors - Perpendicular Plates

The first of the four worksheets finds the view factor for perpendicular plates with a common edge (from the well-known analytical solution) and draws an isometric view of them on the screen. The user inputs the length of the common edge as well as the second dimension of the two plates.

Radiation View Factors - Coaxial Disks

The viewfactor for coaxial, parallel disks is computed from the analytical solution and then they are drawn to scale on the screen. The user inputs the radii of the two disks (emitter and receiver) and the separation distance.

Radiation View Factors - Coaxial Cylinders

View factors for finite-length, coaxial cylinders are computed using a combination of analytical solutions and view factor algebra. The user inputs the radii of the two cylinders and their length. All nine relevant view factors and a scale drawing are returned.

Radiation View Factors - Parallel Rectangles

On the fourth worksheet the view factor for parallel, aligned plates is computed from the analytical solution. The user inputs the length and width of the two rectangles and their separation distance. The view factor and a scale drawing are returned.

Radiation View Factors – Nusselt Unit Sphere Method for Arbitrarily-Oriented Rectangles

The Nusselt Unit Sphere method was developed by Wilhelm Nusselt (for whom the Nusselt number is named) as an experimental method.  His technique was converted to a computational algorithm by a NASA contractor.  See below.

The implementation included in the View Factor Spreadsheet is limited to two arbitrarily-oriented rectangles, but could be extended to other geometries.   The user enters coordinates defining the parallelograms and the algorithm returns the view factor.  A plot of the input geometry allows the user to check his/her inputs.

References:

Howell, J.R., A Catalog of Radiation Heat Transfer Configuration Factors

Modest, M.F., Radiative Heat Transfer, 2nd Ed., McGraw-Hill, 2003.

This spreadsheet provides a systematic template for solving radiative exchange problems involving up to 20 diffuse-gray surfaces.    Spaces are set up for surface radiative properties (area, emissivity) and for view factors connecting all pairs of surfaces.    Surface and spatial radiative resistances are computed from the input, the coefficients of the equations for Radiosity are compiled and the equations solved.    A six-surface example is provided and the spreadsheet automatically sets up and solves the required equations for as many as 20 diffuse-gray surfaces.   Complete derivations of the Radiosity method for black and gray surfaces are provided and a schematic of the equivalent dc circuit is generated.