Sorption isotherms of banana, mango, and pineapple have been experimentally found at 40, 50, and 60 C by use of the salt method for a range of water activities from 0.056 to 0.85. The sorption capacity of these fruits increases with the temperature for a given water activity. The experimental curves have been simulated by the GAB and BET models. The BET model ensures a better representation of the experimental results for water activity lower than 0.35 with maximum deviation of 1.0, 1.5, and 2.0 kgwÁkgdm À1 for respectively banana, mango and pineapple. On the contrary, the GAB model enables the representation of the whole desorption isotherms and the estimation of the water content corresponding to monolayer saturation and of the isosteric heat of sorption. It also takes into account the temperature effect. The isosteric sorption heat of the three studied products are deduced from experimental results and empirical correlations are proposed leading to a satisfactorily representation.
This paper presents a method dedicated to thermal conductivity measurement of thin (a few millimeters thickness) insulating and super-insulating materials. The method is based on the measurement of the temperature at the center of a heating element inserted between two samples, with the unheated surface of the samples maintained constant. A 3D model of the heat transfer in the system has been established and simulated to determine the validity conditions of a 1D model to represent the center temperature. This 1D model was then used to realize a sensitivity analysis of the center temperature to the different parameters. The conclusion is that the thermal conductivity may be estimated with a good precision for all insulating materials from a simple steady state measurement and that the thermal capacity may also be estimated from transient recording of the temperature with a precision increasing with the value of the thermal capacity of the samples. It has then been shown that a device with two samples of different thickness improves the precision of the estimation of the thermal capacity. These conclusions are validated by an experimental study on polyethylene foam and PVC samples leading to an estimation of their thermal properties very close to the values measured by other classical methods (deviation < 5%).
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