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1 April 1992 Evaluation of moisture content in porous material by dynamic energy balance
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The aim of this paper is to describe a procedure to evaluate the moisture content in porous medium by a non-destructive test. The method is based on the determination of the target thermal inertia by means of the measure of the energy input and the corresponding temperature increase, both obtained by 2-D optical sensors. Since the thermal inertia is strongly dependent from the water content, it is possible to estimate the spatial distribution of the moisture. This is done by applying a suitable mathematical model of the porous media accounting for the heat transfer in the transient state. In this phase of the research, we are chiefly interested in the analysis of the surface layer of the sample, so a simple thermal model of the dynamic energy balance can be used instead of a very complicated heat and mass transfer model. Tests are carried out on a series of flat homogeneous samples of bricks. The samples are first desiccated and afterwards conditioned to various known levels of moisture content. Then specimens are submitted to the test procedure, the measured thermal inertia is compared with computed values and correlated with the moisture content obtained following the gravimetric standard method. The test procedure consists in supplying a radiant flux in the visible and near-infrared band to the sample surface. Meanwhile, the local radiating field is carefully mapped using two spot radiometers and a calibrated CCD camera, working in this spectral range. The irradiation field is produced by standard lighting equipment and continuously monitored. The target global absorptivity in the 0.3 - 3 micrometers range is detected as well. The temperature variation is measured by an infrared thermal camera operating in the 8 - 14 micrometers band, linked to a proprietary real time grabbing, processing, and storing digital equipment. The most important information is contained in the initial temperature variation trend, therefore a very fast sampling rate is required. A dedicated software was developed producing the average temperature trend and also the local value of the thermal inertia.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ermanno G. Grinzato, Chiara Bressan, Paolo Giulio Bison, Andrea Mazzoldi, Paolo Baggio, and Cesare Bonacina "Evaluation of moisture content in porous material by dynamic energy balance", Proc. SPIE 1682, Thermosense XIV: An Intl Conf on Thermal Sensing and Imaging Diagnostic Applications, (1 April 1992);

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