(229d) When Things Go Wrong

The junior level unit operations laboratory course usually has objectives that include development of technical writing abilities, reinforcement of concepts learned in previous lecture courses and the acquisition of hands-on experience. Students (singularly or in groups) operate and analyze small-scale industrial equipment (e.g., a centrifugal pump) or measure some physical properties (e.g., thermal conductivity), do some number-crunching, put together a formal report and go on to the next experiment on the schedule. When the experiments all go as expected then the life of the student is relatively stress-free and the above objectives are routinely met. However, equipment problems sometimes intrude on the normal course of events and prevent the ?correct? data from being gathered. Rather than present a barrier to learning, such occasions can provide new insights into the issue under investigation. This paper documents four such cases in which lab ?problems? were used to aid student learning.

In a conduction heat transfer experiment an inaccurate temperature sensor led to errors in the determination of thermal conductivity. Students knew a priori that a sensor was malfunctioning, but did not know which sensor was involved. In a second case students attempting to determine the Reynolds number range over which a flow transitioned from laminar to turbulent were consistently reporting values one third of the ?true' values. In a piping system experiment students attempting to order friction factor values by relative roughness found an order of magnitude discrepancy when comparing one pipe against the others. Finally, in a determination of viscosity experiment, students attempting to quantify the behavior of a shear thickening fluid found instead that the experimental apparatus was indicating shear thinning behavior. In this paper we analyze all these four cases and show how each ?problem? was turned into a learning opportunity.