A Transient Experiment to Determine the Heat Transfer Characteristics of a 100 W Incandescent Light Bulb Operating at 48 W

A simple and inexpensive experiment that illustrates a number of heat transfer principles is presented for use in either the laboratory or the classroom.The purpose of this paper is to describe a transient experiment which determined the heat transfer characteristics of a 100 W light bulb, operating at 48 W. The fraction of the filament power absorbed by the glass envelope was measured and the fractions of the heat transferred from the glass envelope to the surroundings were determined for natural convection, forced convection and radiation.The glass bulb absorbed 26.3% of the filament radiation.At steady state, 64% (8.1 W) of the heat transfer from the glass envelope to the classroom surroundings was by convection and 36% (4.5 W) was by radiation.The calculated natural convection heat transfer coefficient was 7.1 2 and the experimentally determined forced convection coefficient was 12.9 2 .The effective classroom air velocity required to produce this coefficient was 0.6 (1.4 mph), which is in the upper range of air velocities mandated by ASHRAE Standards to keep classroom occupants comfortable in a 26C (79F) classroom.The experimental results indicated that very little of the heat transfer from the filament to the glass bulb occurred by convection through the argon/nitrogen atmosphere within the bulb; essentially all heat transfer from the filament to the bulb was by radiation.