Characterization of Hydrolytic Degradation of U-f Joints Through Apparent Diffusivity

The hydrolytic aging of an adhesive joint (wood-urea/formaldehyde resin) is characterized by measurements of the apparent diffusivity of two inert gases within the bond. This kind of measurement is of some interest, because it includes both chemical and geometrical changes in joint structure.Apparent diffusivities are determined in a diffusion cell after various degradation times in a cold water bath. Our results show that diffusivity increases with aging time with an asymptotic trend. Nevertheless, when the joint undergoes cyclic aging (immersion/drying), chemical degradation occurs mainly during the first cycle, while mechanical degradation observed during the drying steps also appears during the following cycles. The values of apparent diffusivity show that the solute transport is a real diffusional transport phenomenon and that resin joints are not porous

Modeling of transient mass transfer of a gaseous component in an isothermal porous adsorbent

The present study is avoided to a better understanding of the complexity of the adsorption process of a gaseous constituent on a porous solid (wood) with the purpose to improve the modeling. During the sorption on the porous solid, the diffusion mass transfer of the gaseous substance A occurs simultaneously in gaseous and adsorbed phases. The mass balance equations are written for the simultaneous diffusion transfers. The thermodynamic equilibrium between the phases is also represented. Four different models have been compared. Numerical results have been compared with experimental data and show that the hypothesis of equilibrium conditions between the gaseous and the adsorbed phases is not always verified

Biochar as a catalyst for hydrogen production from methane conversion

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Using a parametric study to analyse the performance of wood solar dryers with glazed walls

Parameters characterizing wood and air were studied in order to analyze the performance of a wood solar dryer functioning under Moroccan climate. A mathematical model based on the climate data of Rabat city was used to investigate theoretically the wood drying process. Two wood speciesthuya (Tetraclinis articulate) and pine (Pinus pinaster)-were examined in the present study. The results obtained by computer simulations are in good agreement with the experimental values. Furthermore, our findings indicate that the use of a global mass transfer coefficient for low temperature convective and homogenous drying conditions allows the influence of the principal operating parameters (wood thickness, wood density, air temperature, air velocity and ventilation mode) on the drying time to be estimated with great accuracy. Analyses pertaining to the two studied wood species revealed that(1) pine dries more quickly than thuya, (2) the drying process is faster in the summer relative to other seasons, (3) increasing the air velocity by 100% results in a 20% reduction in the drying time, and (4) continued ventilation reduces the drying time by 43%.   PDF XM

Experimental study of thermal effect on olive wood porous structure during carbonization

The study presented in this paper is an investigation on the porosity changes induced by the carbonization of Tunisian olive wood. The porosity is measured by mercury porosimetry. The experimental results show that the total porosity of carbonized wood increases with the temperature. It should be underlined that the formation of some macropores during the increase of the temperature is certainly due to the breaking of the cell wall by the mercury penetration. The weakness of the cell wall is observed when the degradation rate of the three pseudo components of wood, the notion of which has been introduced by the authors in a previous article [Grioui et al. 2006], becomes high which corresponds to the temperature range between 523 K and 548 K

Solar drying of pine lumber: Verification of a mathematical model

This work presents verification of a mathematical model for drying of a wood stack in a greenhouse type solar dryer. A simplified heat and mass transfer numerical model has been developed with input parameters based on the actual metrological data of a Moroccan climate. For its validation, a comparative study is performed in this work; the present model is solved to simulate the solar drying of pine wood using experimental data of previous wood drying experiments. The average relative discrepancies between the model predicted and experimental data are 1,2% for wood moisture content, 1% for drying air temperature and 5% for the air relative humidity. The close agreement between the predicted and experimental results shows the ability of the model to reproduce experimental drying data for wood

Modeling and simulation of an industrial indirect solar dryer for Iroko wood (Chlorophora excelsa) in a tropical environment

This paper presents a modeling of an instrumental indirect solar wood dryer less expensive functioning in a Cameroonian climate applied to the climate of Yaoundé. The dryer is easy to build and electric energy is only used for the fan. Applications are done on Iroko wood (Chlorophora excelsa), a tropical wood 50mm thick most utilized in Africa. A satisfactory agreement between experimental and numerical results was found. Influences of thickness, wood initial water content and airflow rate were studied

Modelling of a solar wood dryer with glazed walls

This work present a study of a solar wood dryer in a Moroccan climate. The wood drying process is investigated theoretically by a mathematical model based on actual climate data. The model constantly gives dryer humidity and temperatures (air and walls) as well as wood temperature and moisture contents. For verification, the present drying model is executed within the simulation program with experimental data of wood drying experiments conducted in two dryers located in two different sites. The computational results show a reasonable agreement between the predicted and measured wood moisture content.Este trabajo presenta un estudio de un secador solar de madera en un clima marroquí. El proceso de secado de madera es investigado teóricamente desarrollando un modelo matemático basado en datos climáticos reales. El modelo da a cada momento, la humedad y la temperatura  del secador (aire y paredes) así como la temperatura y la humedad de la madera. Para la verificación experimental, este modelo de secado es introducido en el programa de simulación con datos experimentales de secado de madera de los experimentos realizados en dos secaderos situados en dos lugares diferentes. Los resultados muestran un acuerdo razonable entre la humedad de la madera predicha y medida experimentalmente. 

Sorption behavior of four tropical woods using a dynamic vapor sorption standard analysis system

Sorption behavior of four tropical woods coming from Cameroon is studied using a Dynamic Vapor Sorption-Intrinsic apparatus. Sorption isotherms at 20°C and 40°C of Triplochiton scleroxylon (obeche), Entandrophragma cylindricum (sapele), Sterculia rhinopetala (lotofa) and Terminalia superba (frake also called limba) are compared to those in the literature with methods using saturated salts for lotofa and frake with satisfactory results. Experimental values are fitted using two sorption isotherm models. Sorption hysteresis is greatest in sapele and least in frake. When temperature increases, differences in the hysteresis of sorption among the woods decreases. Hystereses of all studied woods ranged from 0,5 to 3%. Our studied woods have lower equilibrium moisture content probably caused by the higher values of extractives content. The water sorbed molecules on multilayer during both adsorption and desorption at 20°C and 40°C is greater in the case of frake and lower in the case of lotofa. The water sorbed molecules on multilayer of sapele is greater than those of obeche. The predominance of multilayer over monolayer of our woods is from 0,2 to 0,4 relative humidity in adsorption phase, and from 0,3 to 0,4 relative humidity in desorption phase