Salt Lake City, Utah
June 23, 2018
June 23, 2018
July 27, 2018
An activity is described in this paper to introduce freshman students to the concept of heat loss due to convection heat transfer. The activity is part of an introductory course to mechanical engineering. The overall goal of the introductory course is to help students learn concepts in mechanical design, forces and stresses, engineering materials, motion and power transmission, and thermal and energy systems. The course has several different activities. The goal of the particular activity described in this paper is to cover the thermal systems portion of the class. In the activity, a ball bearing (sphere) is specified to have a given diameter and initial temperature. A tutorial is given to help students draw the sphere in SolidWorks and define its material. The thermal utility of SolidWorks is used to set initial conditions, a convection heat transfer coefficient, an ambient temperature, and run a transient heat transfer simulation. The numerical simulation is treated as a lab experiment and emphasis is placed on the results while only basic instructions are given to manage mesh independence and numerical convergence. As they run the simulation, the students can visually see the color of the sphere change, indicating it is cooling over time. The students also create cuts through the sphere at different simulation times to discover that the temperature in the middle of the sphere is typically higher than the temperature at the surface. When the ball bearing is steel and the cooling fluid is air (Bi < 1), the temperature gradient can be a very small fraction of one degree Celsius. The students plot the average temperature of the sphere versus time as calculated using SolidWorks. Since cooling a sphere due to convection has an analytical solution for Bi < 1, the analytical equation is provided to the students. They are asked to generate a plot of temperature versus time using the analytical equation. Comparing the temperature versus time curve obtained by SolidWorks to that obtained using the analytical equation can show quite a difference when there is an error in the calculations. However, when the calculations are correct, the curves are found to have excellent agreement. The students are given a lecture on heat transfer before doing this activity. The physics of cooling a sphere using convection is described in the lecture. When the students come to perform the activity in the lab, they are paired into teams and each two students are asked to work together. They generate an engineering report showing their input data, results, and conclusions. The teams are assessed based on their ability to run the simulation, use the analytical equation, make the comparison, and provide a meaningful conclusion. A rubric is developed and teaching assistants (TA) are asked to grade. Grading the reports indicate a high level of attainment of the project goals. The TA’s load will be described and examples of the conclusions will be provided in the paper. The activity is implemented in classes of 48 students (Fall Semester) and other classes of over 200 students (Spring Semester). The project is scalable and can be applied in any mechanical engineering freshman class. It is found to have no limitations based on the class size as long as computers are available with the SolidWorks or equivalent software. A survey is used to capture the student’s perception of the activity. Results of the survey indicate the activity is well appreciated by the students. Results of the survey will be included in the paper.
Fadda, D., & Rios, O. (2018, June), Introduction to Heat Transfer in a First-year Mechanical Engineering Course Paper presented at 2018 ASEE Annual Conference & Exposition , Salt Lake City, Utah. https://peer.asee.org/30719
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