Investigating convective heat transfer with an iron and a hairdryer

Abstract

A simple experimental set-up to study free and forced convection in undergraduate physics laboratories is presented. The flat plate of a domestic iron has been chosen as the hot surface, and a hairdryer is used to generate an air stream around the plate. Several experiments are proposed and typical numerical results are reported. An analysis and discussion of the results can be useful even for students at the most elementary levels; for higher levels, comparisons between the measured heat transfer coefficients and the well-established empirical correlations are included, showing good agreement.

Fourier analysis of thermal diffusive waves

“…Several laboratory experiments investigating radiative and convective heat transfer can be found in the literature. [8][9][10]…”

Scales of free convection around a vertical cylinder

“…The scale analysis starts by defining a cylindrical control volume of (unknown) thickness δ and height z around the cylinder (figure 1). The heat flow from the wall is of the order of 2πr 0 zk T /δ, where T = T w − T ∞ and k is the thermal conductivity of the fluid 1 . The thermal energy is carried away by an enthalpy stream occupying the annular area A = π(d + δ)δ, where d = 2r 0 .…”

“…It is only for values of the Prandtl number close to unity (most gases and liquids, including air and water) that all three forces are of the same order of magnitude. 1 In this paper the concept of the order of magnitude with accompanying symbol ∼ is used in an intuitive sense. A more precise definition is given in [3].…”

“…As has recently been remarked [1], in some physics and engineering curricula convective heat transfer may be given relatively little attention in comparison with conduction and radiation. The reason for this is that solutions to problems in convection are for the most part based on experimental correlations involving numbers that originate in dimensional analysis [2].…”

An experiment in heat conduction using hollow cylinders

“…It is one of the three basic mechanisms of heat transfer and the most widely explained in undergraduate textbooks, with the statement of the basic Fourier law and the definition of parameters such as thermal conductivity or thermal resistance [2]. Conduction refers to the transfer of thermal energy between neighbouring molecules in a substance due to the existence of a temperature gradient.…”