Thermal Mutual Inductance

Abstract

WHEN heat is dissipated from a hot body immersed in a fluid, the flow of heat is accompanied by a mechanical circulation of the fluid in the system of natural convection currents. The stored kinetic energy bestows on the heat current a property which has been termed ‘thermal ‘inductance, and curves I have obtained¹ for the thermal transients consequent on the sudden heating of a cylindrical body, or wire, immersed in a fluid, clearly show the influence of this inductive element. Experiments of this nature may, however, readily be extended to show the influence of a property which may be referred to as ‘thermal mutual ‘inductance. If we take two parallel wires, one vertically above the other so that the same system of convection currents link both, then any change in the heat flow from one might be expected to influence the heat flow from the other. There are two such changes possible, a transient and a permanent one. A steady change in the heat flow from the upper wire consequent on a change in the heat flow from the lower simply represents the case of a hot-wire anemometer used to explore natural convection currents. If, however, our system is to exhibit a property of thermal mutual inductance, then we expect a transient change in the heat flow (or associated temperature difference) from the upper wire to accompany any change in the heat flow from the lower.