A Guided Inquiry Approach To Teaching Fan Selection

The selection of a fan for sufficient airflow for a particular system involves much more than determining the flow requirements and selecting a fan out of a catalog. A designer must understand that the flow rate of a fan is dependent on the amount of backpressure in the system while the backpressure depends on the flow rate. The characteristic curve for a fan and the impedance curve for a system show these dependencies. The actual amount of flow that a fan will deliver to a given system is determined by the intersection of these two curves. Students could be taught about this as part of a traditional lecture. The exercise described in this paper is an attempt to enhance their learning experience through a guided inquiry laboratory exercise. The students learn to generate both the fan and system characteristic curves. The curves are used to predict the actual flow rate of a fan in an application. Once the fan is mounted into the device the actual operating flow rate is determined. As part of the exercise the students also plot characteristic curves for fans in series and in parallel to determine what happens in those configurations. The system used for the exercise is a familiar computer power supply. This exercise has been implemented twice in small groups. The first time the subject was introduced in a lecture which included an in class demonstration. The second time the exercise was used to introduce the topic. A lecture during the next class was used to answer any questions the students had about the topic. This paper discusses the learning objectives, equipment, procedure and preliminary findings from the two implementations. Also, the optional in-class demonstration is discussed.