Examining student misconceptions of conservation of mass and energy in pipe flow using very low cost experiments

Abstract

Misconceptions concerning how to apply conservation of mass and energy to engineering systems plague many of our undergraduate students. For example, many students struggle with understanding how to use conservation of mass to predict fluid velocity in a pipe or how to use conservation of energy to predict pressure drop in a pipe. In this study, the use of very low cost fluids experiments is investigated to examine and correct student misconceptions connected to Conservation of Mass and Energy in pipe flow. The approach documented here takes advantage of simple, inexpensive, easy to use experimental hardware to enable students to make measurements and observations that directly challenge their misconceptions. In particular, this paper looks at the implementation of very low-cost pipe flow experiments in large Mechanical Engineering lecture classrooms to examine how hands-on active learning can supplement more traditional lecture classes to deepen student understanding of engineering principles. The low-cost pipe flow experiment was fabricated using a four step approach: (1) the geometry of the pipe flow experiment was defined using CAD software, (2) A plastic mold of the experiment was 3-D printed using rapid prototyping, (3) the experimental geometry was molded in thin plastic sheets using vacuum forming, and (4) the final experiment was assembled from the vacuum formed sheets to produce multiple copies of the experiment. The resulting experimental hardware was simple, robust and inexpensive enough to distribute individual copies to groups of four students with the cost to each student in the class much less the price of a textbook. The pipe flow experiment was implemented in junior-level fluid mechanics classes with 106 students. The students were divided into two groups, one of which worked with the low-cost experiment, the others received a lecture presentation of the same material. The efficacy of the hands-on experiments in clarifying student understanding of the conservation laws was assessed via pre and post quizzes given to all students before and after either they did the hands-on experiments or they attended a lecture on the same material. After the intervention, significantly more students who participated in the hands-on experiment demonstrated an understanding of the linear pressure drop in a pipe than students who attended a lecture on head loss.