June 20, 2010
June 20, 2010
June 23, 2010
Division Experimentation & Lab-Oriented Studies
15.161.1 - 15.161.14
An Inquiry-Based Exercise Involving a Tank of Water with a Hole in its Side
The tank draining exercise is part of a larger study on inquiry-based laboratory exercises for undergraduate engineering courses in the fluid and thermal sciences. Our research involves the development of the curricular material, measurement of learning gains, and measurement of changes in student attitude toward laboratory work. In this paper we discuss the laboratory hardware, the laboratory procedure, and typical results of using the tank draining hardware.
The tank draining exercise provides a laboratory experience to teach students about transient, incompressible flow. Draining of a tank is one of the few practical applications of transient flow that can be analyzed at the level of fluid mechanics knowledge typical of undergraduate engineering students. Mass conservation is applied to the tank to relate the change in height of the free surface to the exit velocity from the hole in the side of the tank. The tank draining experiment also affords a discussion of the whether hydrostatic pressure equation can be applied when the fluid is moving. This issue is explored in the pre-lab reading assignment.
In addition to addressing core concepts of fluid mechanics, the tank draining exercise is designed to develop qualitative reasoning skills. We define qualitative reasoning as the ability to predict trends in the behavior of a system from direct observations (experimental evidence) and qualitative manipulation of mathematical models. This skill is especially useful in a laboratory setting or on a factory floor where there may not be time to perform a detailed engineering analysis. Qualitative reasoning is described by the common expressions “thinking on one’s feet”, “using engineering experience”, and “back of the envelop calculation”.
Qualitative reasoning is a kind of higher order thinking practiced by experienced engineers. A laboratory exercise provides opportunities to develop and demonstrate qualitative reasoning skills because the system response can be predicted and then observed with minimal formal analysis. In the tank draining exercise, students make measurements on one tank. They are then asked to predict the results of repeating the measurements on a tank with a different shape. After making their predictions, they perform the measurements that provide immediate feedback on the accuracy of their predictions.
Similar tank draining experiments have been used in class demonstrations, in science museums, and by other authors1-4. For example, the supplemental material to the textbook by Munson, Young and Okiishi4 includes a video of water draining from three holes in a two liter soda bottle. Libii1, and Libii and Faseyitan2 describe a tank-draining experiment where the drain orifice is at the bottom of the tank. Saleta et al. use a configuration similar to that in Figure 1,
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