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VERSATILE, LOW COST CONVECTIVE HEAT TRANSFER LAB

Timothy C. Scott, Claude H. Mitchell

University of Virginia

Abstract

Illustrations of external convection generally require wind tunnels or expensive purchased modules. This paper describes a versatile, bench top rig for external free and forced convection which may be constructed for less than $200. The low cost allows enough units to be built so that students may work in small groups. The rig uses a common hair drier as the air source with a simple box to create a hot or cold jet. Various objects placed at different distances from the air source provide for Reynolds number variations. Experiments and test objects are described for transient heating and cooling of spheres and free and forced convection from a heated disc. The effects of free stream turbulence on forced convection can also be demonstrated. A web site is given from which the manuals and details of the rig may be obtained.

Introduction

Experiments to illustrate the phenomena of forced and free convection are a very important part of engineering heat transfer courses. The need for such laboratory work is increasingly important as more of our students arrive with little or no practical experience.

Several commercial equipment rigs may be purchased for external free and forced convection demonstrations. While these are smaller and more portable than most older experiments based on fixed wind tunnels, they are quite expensive. This means that most institutions will have only one of each. In large classes, this limits the amount of interaction that any individual student may have with the equipment.

A number of institutions have created some effective low-cost rigs for various heat transfer studies. For example, Cloette [1] used the temperature distribution in a copper rod acting as a fin to measure the forced convection to air from a fan. Erens [2] blew air over vertical hollow tubes of various cross sectional shapes with steam condensing on the inside. Mullisen [3] describes projects in which students instrument heated cylinders and attached them to bicycles, moving cars, immersed in flowing streams, etc. to determine forced convection. Campo [4] heated stainless steel spheres in an oven and then exposed them to still air.

Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright  2004, American Society for Engineering Education

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Scott, T. (2004, June), Versatile, Low Cost External Convective Heat Transfer Apparatus Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--13626