Abstract
The insulating materials and conditions described in the paper are those relating to such temperatures as are likely to be met with in heating, cooling, ventilating, or refrigerating practice. The symbols and nomenclature used are those adopted by the Committee on Heat Transmission of the National Research Council (U.S.A.).
The first section describes respectively, the hot-plate and hot-box methods of testing, the former being the more suitable for materials which are comparatively homogeneous, and the latter for walls or other built-up sections. Illustrations are given of the hot-plate apparatus at the University of Toronto, on which much of the experimental work was performed. It is frequently impossible to compare tabulated values of heat conductivity because of differences in test conditions, and accordingly in the second section the effects of (a) mean temperature and temperature coefficient, (b) differences of temperature on the hot and cold sides, (c) superficial pressure, (d) surface resistance, and (e) time effect, are considered in detail and an attempt is made to indicate their relative values. A table of characteristic conductivities is given at the end of the paper. The third section deals in a similar manner with the effects of differences in the materials themselves or in their application. These include the influence of: (1) size and thickness of samples, (2) laminated structure, (3) density of fibrous and cast materials, (4) air spaces in materials or structures, (5) moisture, and (6) infiltration of air or gases.
The objective in all cases is to obtain the greatest insulating value per unit of cost, and this is not always favourable to the use of material having the lowest conductivity. Structural strength and resistance to fire, moisture, and vermin are frequently important factors. The paper concludes with some statistics concerning the production and consumption of insulating materials in Canada.
Get full access to this article
View all access options for this article.