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Laboratory Demonstrations/Experiments in Free and Forced Convection Heat Transfer Introduction

A number of papers have been written recently on methods for improving or supplementing the teaching of heat transfer including the use of spreadsheets to solve two-dimensional heat transfer problems1, a new transport approach to teaching turbulent thermal convection2, the use of computers to evaluate view factors in thermal radiation3, and a new computational method for teaching free convection4. Supplemental experiments for use in the laboratory or classroom have also been presented including rather novel experiments such as the drying of a towel5 and the cooking of French fry-shaped potatoes6. Hunkeler and Sharp7 found that 42% of students in senior laboratory over a four year period were Type 3 learners, that is, action-oriented “hands- on” common sense learners. Thus, an excellent method for reinforcing course content is to actively involve students in laboratory exercises or demonstrations which are designed to compare their experimental data with data or correlations from the literature.

As part of the combined requirements for CHEG 3143, Heat Transport, and CHEG 3232, Laboratory II, junior level chemical engineering students at the University of Arkansas were required to perform simple heat transfer experiments or demonstrations using inexpensive materials that are readily available in most engineering departments. During the first offering in the Fall semester of 2004, the students were required to design, implement and analyze the results from basic experiments. During the second offering in the Fall semester of 2005, the students were asked to suggest and implement improvements in the basic experimental design which could lead to better agreement between their experimental results and results from literature correlations. This exercise has several benefits: • It provides an opportunity for students to have additional “hands-on” experience; • It demonstrates a physical application of correlations found in the textbook; and, • It helps students develop an appreciation for the limitations of literature correlations. Results from three of these experiments (free convection cooling of an upward-facing plate, forced convection cooling by flowing air over an upward facing horizontal plate, and forced convection heating of a rod by flowing air through an annulus) are described below. In addition, survey and test results are presented which help to demonstrate whether the experiments/demonstrations improved or enhanced the students’ understanding of the appropriateness and limitations of heat transfer correlations found in the literature.

Free Convection Heat Transfer from an Upward Facing Horizontal Plate

Free convection heat transfer is encountered in many practical applications, including heat transfer from pipes, transmission lines, baseboard heaters and steam radiators. Correlations are available for predicting free convection heat transfer coefficients for many different geometries. One of the important geometries is the upward facing horizontal heated surface or plate, the subject of this investigation. The overall objectives of this experiment were to: 1. Determine the experimental free convection heat transfer coefficient for the top surface of a horizontal hot plate exposed to air, and

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Clausen, E., & Penney, W. (2006, June), Laboratory Demonstrations/Experiments In Free And Forced Convection Heat Transfer Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--867