Yves Jannot

Experimental Determination and Modeling of Sorption Isotherms of Tropical Fruits: Banana, Mango, and Pineapple

Abstract 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 kgw · kgdm−1 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.

Modeling of Banana Convective Drying by the Drying Characteristic Curve (DCC) Method

Abstract Experimental convective drying tests of banana have been carried out for different air conditions to show the influence of air temperature, absolute humidity and speed on the drying rate. The analysis of the drying rate evolution as a function of product water content enables the identification of fourth drying phases: temperature rising (phase 1), exponentially decreasing drying rate (phase 2), linearly decreasing drying rate (phase 3) and very low drying rate (phase 4). The temperature rising phase 1 being very short and the last phase 4 being not reached during typical drying, the drying characteristic curve (DCC) has been represented by two different mathematical functions fitting phases 2 and 3. Their parameters have been determined by minimization of the quadratic errors between experimental and theoretical curves. It leads to a unique curve (the DCC) representing all air drying conditions the integration of which enables the calculation of the product water content with a maximum error of 0.09 between experimental and simulated values.

Transient hot plate method with two temperature measurements for thermal characterization of metals

This paper presents a study of the transient hot plate method with simultaneous measurements of front (heated) and rear face temperatures. In contrast to the classical device, a single sample of the material to be thermally characterized is set in contact with a planar heating element and inserted between two pieces of insulating material. The purpose was to simultaneously estimate thermal effusivity and conductivity of metals in a limited time t2 ( 30 s. The thermal effusivity is estimated between 0 and t1 by minimization of the quadratic errors between the experimental curve and the simulated curve T0(t). The thermal conductivity is estimated between 0 and t2 by minimization of the quadratic errors between the experimental curve and the simulated curve T2(t). To validate the model and the estimation process, experimental tests were realized on four samples of metals with conductivities varying from 6 to 140 W m−1 °C−1 and having typical area 44.5 × 44.5 mm2 and thickness varying from 16.7 to 80 mm.

A quadrupolar complete model of the hot disc

The hot disc method is a transient plane source method used for the estimation of the thermal conductivity and diffusivity of solid materials. A complete model based on the thermal quadrupoles formalism has been developed to represent the hot disc temperature variation. This model takes into account both the thermal contact resistance between the solid to be characterized and the hot disc and the thermal inertia of the hot disc. It makes it possible to realize the parameters estimation on all the recorded temperature measurements. This model is used to highlight the estimation uncertainty due to approximations in the heat transfer model.

MEASUREMENT ERRORS PROCESSING BY COVARIANCE ANALYSIS FOR AN IMPROVED ESTIMATION OF DRYING CHARACTERISTIC CURVE PARAMETERS

ABSTRACT The aim of this paper is to show the interest of the covariance analysis applied to measurement error in the particular case of the identification of a drying characteristic curve from experimental drying data. The modelisation of drying by use of the Drying Characteristic Curve (DCC) method is first presented with usual specifications (power function, critical moisture content …). The experimental procedure used to obtain drying curves and the data processing are detailled and analysed. Measurements errors are identified at the first step of the procedure and their effects on the estimation error of the exponent α of the power function are estimated. Three different methods for estimating α are presented under their matrix form: the least square method and two methods based on the «Gauss–Markov» or «Maximum likelihood» theorem, firstly under a simplified form suited if the estimation errors are uncorrelated and secondly under a complete form suited even if the estimation errors are correlated. These three methods are applied to experimental results obtained with ginger roots drying. The value of the exponent α of the power function and then the distances between the three corresponding theoretical drying curves (representing product water content vs. time) and the experimental points are studied. It is shown that in this particular application, the complete Gauss–Markov method leads to the better fitting and that the simplified Gauss–Markov method, since it is a priori non appliable in this case where errors are correlated, gives quite better results than the oridnary least squares method. The covariance matrices of the estimation errors of reduced water content, reduced drying rate and exponent α are also presented in order to show the correlations existing between the measurement errors of each variable during a drying cycle.

INVESTIGATION ON THE USE OF THE CEMENT MORTAR CONTAINING BANANA FIBERS AS THERMAL INSULATOR IN BUILDING.

This paper dealed with the valorization of Benin natural resources through the development of new composite materials made of banana fibers-cement mortar which could be used as thermal insulator in building. The developed composites were formulated and made by substituting a mix of sand and cement, in mass fractions, with the banana trunk fibers previously washed with hot water and dried. Cement was dosed at 250 kg m-3 of mortar and the ratio W/C was equal to 0.7 for the samples. The effected thermal tests by the hot plate method using two temperature measurements had shown a decreasing of the thermal effusivity and conductivity when the proportion of fibers increased. One had obtained the respective relative deviations of 25.54%, 56.09% and 65.68% between the thermal conductivity of the reference sample, which was equal to 1.14 W m-1 K-1, and that of the composites. These results made the composites interesting thermal insulators in building with reduction of the normally used quantity of cement and sand and valorization of agricultural waste. The water absorption was also calculated for each sample.