A Laboratory Exercise To Demonstrate How To Experimentally Determine The Operating Point For A Fan

Students often have a difficult time understanding how to determine the operating point for a fan when it is placed into a system. They first have to gain some understanding of fan curves and system flow impedance curves. Then they must superimpose the curves to determine the actual operating point. This can be explained within the context of a lecture, but students seem to gain a better understanding of the concept by actually finding the operating point of a fan in a laboratory setting. This paper describes one such exercise than can be used for this purpose. In order to run this exercise the students must first learn to generate fan curves and system impedance curves. These preliminary exercises are briefly discussed in this paper. Once they have acquired those skills they proceed to test a real system to determine the fan operating point. An ordinary power supply from a personal computer is used for the demonstration because most of the students are very familiar with the device. The students are required to plot a system flow impedance curve for the enclosure and a fan curve for the fan. They plot both curves and predict what the actual operating point for the fan is when installed in the power supply. Finally, they physically install the fan and measure the actual operating point to see how close they have predicted the actual value. For exercises like this to be instructive, the students must have a real chance to be successful. The results of this exercise depend heavily on how carefully the students take their measurements for the fan curve and the flow impedance curve, but when reasonable care is taken they can predict the actual operating point within 5% or less. Values within 1% are not uncommon. This gives the students an outstanding chance of a successful outcome. This paper discusses the equipment used, the preliminary work to learn to produce the necessary curves, the final exercise, and a set of typical results.