Measuring moisture content in porous insulation materials based on transient temperatures over a period of 100seconds

摘要

Porous materials can absorb large amounts of moisture under high-humidity conditions. Numerous methods have been developed to determine moisture content, but a rapid, inexpensive and accurate measurement method is lacking. The current investigation proposed the measurement of moisture content in porous materials based on transient temperature responses over a period of 100seconds. A lacquered nichrome wire was used as the heating element, and the transient temperatures were monitored by two highly sensitive fiber-optic sensors. Through curve-fitting of the transient temperature responses with the composite heat conduction theory, the volumetric heat capacity (product of the density with the specific heat) of the tested material was inferred. The moisture content was determined from the difference in the volumetric heat capacity of the material with respect to its dry state. The above method was used to quantify the moisture content of sponge blocks with volumetric moisture mass ranging from 0 to 75kg/m(3). Two series of isolated tests were conducted to evaluate the repeatability of the measurements. The maximum difference in the measured volumetric moisture mass between the proposed method and the gravimetric method was less than 7kg/m(3), and this accuracy is sufficient for engineering applications.