Measuring moisture content in building insulation materials by a hot film

Abstract

In a humid environment, porous insulation materials can acquire large amounts of moisture, which worsens the materials’ performance and causes corrosion. Current thermal methods to measure moisture content in porous materials require that a temperature sensor be placed some distance away from a heating element. As a result, the measurement is very sensitive to the distance between the heating element and the sensor. In addition, the required large heat flux induces unwanted convection and radiation heat transfer that interfere with the measurement. To solve these problems, this investigation proposed a hot film with two thermocouples attached to measure the moisture content. The hot film was embedded in the test material for a constant heating of 90 s. The sensed temperature rise rate for the final 50 s was obtained to infer the volumetric heat capacity for moisture content. The proposed method was used to measure moisture in sponge blocks with different moisture contents. By comparing the measured moisture contents with those determined by gravimetric weighing, it was found that the hot film method accurately measured the moisture in porous materials. The hot film method was more sensitive to low moisture content in porous materials than to high moisture content.