Lecture 07 (2014). Transient heat conduction. Plane walls, cylinders and spheres

This lecture continues with unsteady/transient heat conduction, specifically in large plane walls, long cylinders and spheres. After the exact equation for one dimensional heat transfer was derived in previous lecture an example is done. The example is about a dead body with temperatures known and the problem is to found the time of death. Two approaches are used. The first approach using a lumped system approach which should not give good results as the Biot number is too large. The second approach is to use a one term approximation. The one term approximation was first done incorrectly to illustrate that the Biot number calculation for the lumped system approach cannot be used. Thereafter it was done correctly using the correctly calculated Biot number. The lecture was based on the textbook of Cengel and Ghajar (4th edition) and was presented as part of a heat transfer class to the fourth year students of the Department of Mechanical and Aeronautical Engineering by Prof Josua Meyer, Head of the Department of Mechanical and Aeronautical Engineering of the University of Pretoria, South Africa. Lecture was presented on 12 February 2014.