Moisture Gain of Spray-Applied Insulations and Its Effect on Effective Thermal Conductivity-Part I

Abstract

The presence of free water in fibrous insulating materials can have a very det rimental effect on their thermal and physical properties. Fiberglass and cellu lose insulations were spray-applied to horizontal aluminum plates and exposed to air at relative humidities of 30, 50, and 70% and temperature differences of 20 and 27 C°. The moisture gain was determined by periodically weighing the samples, and the effect of the moisture on the heat flow and temperature distri bution was measured by heat flow sensors and thermocouples. Drying was also investigated by reducing the relative humidity to 10% once steady state had been reached. The rate of moisture gain and the total moisture gain increased with increasing relative humidity and temperature difference, and, after an initial increase, the apparent thermal conductivity would attain a quasi-steady state value that was directly proportional to the moisture gain.