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How Do I Calculate View Factors for Radiant Heat Transfer?

All objects emit heat. That heat is absorbed by other objects. A view factor is a means of showing how much of the heat is absorbed. A simple example is a pot on a stove. The pot absorbs some of the heat; that's the process that cooks the pot's contents. The rest of the heat warms the kitchen. Calculation of the view factor tells you the efficiency of the stove.

Geometric Shape
- You must first identify the geometric shapes. This is due to the fact that different shapes produce different view factors. At the home page of R.J. Ribando at the University of Virginia, he identifies four common geometric configurations. Those shapes include perpendicular plates with common edges and parallel disks. The other two configurations are coaxial cylinders and parallel rectangles. Each configuration has two geometric objects so the view factor can be calculated for heat transfer from one object to the other.
Measurements
- After identifying the geometric shapes measurements are required. For example, to calculate the view factor for two parallel disks, three measurements are needed. The first measurement is the radius of the receiving disk. Next, you need the radius of the emitting disk; the one producing heat. Finally, you need to measure the distance between the two disks. In this simple example, you're now ready to calculate the view factor. For simplicity, assume both radius are 4 and the distance is 2.
Calculations
- Calculations to solve the view factor for parallel disks start with the creation of a fraction with the separation distance as the numerator or top number. The denominator, or bottom number, is the radius of the emitter. Divide the numerator by the denominator. Your answer is 2 divided by 4 or 0.50. Next, create a fraction with the radius of the receiver as the numerator and the distance as the denominator. You have 4 divided by 2 or 2. These numbers translate into a view factor of 0.610, according to the Indiana University software.
Software
- Calculation of view factors for anything other than simple objects requires complex mathematical computations. Software exists to do the calculating for you. Your part is inputting the necessary information for the computer to make the calculation. This involves items such as distance between the objects, angles and measurements; basically the same data needed for a simple problem.

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