The Influence of Through-Metal on the Heat Loss From Insulated Walls

Abstract

Abstract The heat flow through insulation containing “through-metal,” or “thermal short-circuits” has been investigated. The heat flow through such a structure (occurring, for example, in the insulation of ship hulls) can be considerably larger than would be found from adding to the heat flow through the insulation that contributed by the “through-metal,” as if the two were independent. Thus the apparent effectiveness of an insulation can be very much smaller than would be calculated from the thermal conductivity alone. From the many different forms of thermal short-circuits, one specific type has been selected for investigation, i.e., that of metal strips or fins extending through insulation which is covered on its surfaces by sheet metal. General curves are developed and their application explained, from which an “increase factor” for any condition (conductivity and thickness of the insulation, conductivity and thickness of the strips, outside film conductance) can be read. The “increase factor” is defined as the ratio of the heat flow through an actual structure, compared with the flow that would occur if the insulation and heat flow through metal strips were independent of each other. The method of developing these general curves and the basis of the experimental technique used are explained in two Appendixes.