Experimental study and modelling of water sorption/desorption isotherms on two agricultural products: Apple and carrot

This work is focused on some properties of dried apple (Red Chief) and carrot (Misky). Water sorption isotherms of carrot and apple were investigated at three temperatures: 30, 40 and 60°C, corresponding to drying temperatures, by the static method consisting of the use of different sulphuric acid solutions. Guggenheim-Anderson-de Boer (G.A.B) model is found to describe the experimental curves better than Henderson, Hasley and Oswin models with a correlation coefficient superior to 0.97 for both products. The hysteresis phenomenon was clearly observed in the case of apple isotherms. The experimental data were also used to determine the isosteric enthalpy of desorption of apple and carrot. The isosteric enthalpy of desorption decreased with increase in moisture content and the trend became asymptotic

Étude du phénomène de colmatage chimique des distributeurs d'eaux utilisés en microirrigation

Les périmètres irrigués du Cap Bon sont alimentés principalement par les eaux du Canal Madjerda Cap Bon, les eaux de barrages et les eaux souterraines. Plusieurs techniques ont été testées par les agriculteurs dont la micro-irrigation se trouve la plus efficace. L'utilisation de ce système a révélé un problème d'entartrage des distributeurs. A cet égard, nous avons mené une étude complète permettant de connaître la qualité des eaux utilisées et de les caractériser selon leur pouvoir colmatant. L'analyse physico-chimique a montré que la majorité de ces eaux est caractérisée par une minéralisation favorisant une bonne culture, et que les fortes teneurs en calcium, magnésium et nitrate sont attribuées aux eaux des puits de surface. La caractérisation des eaux étudiées selon leur pouvoir entartrant a été effectuée au moyen de la chronoélectrogravimétrie CEG: On provoque la précipitation forcée du carbonate de calcium à une électrode indicatrice, par réduction de l'oxygène dissou à -1V/ECS (électrode au calomel saturée de chlorure de potassium) Cette technique a montrée que le pouvoir incrustant de ces eaux croît dans l'ordre: eaux des barrages ‹ eaux des forages ‹ eaux de Canal Madjerda Cap Bon ‹ eaux des puits de surface. L'inhibition chimique de la précipitation du carbonate de calcium apparaît comme une méthode de choix pour lutter contre l'entartrage des distributeurs d'eaux utilisés en micro irrigation. L'efficacité de trois inhibiteurs HMPS, STPP et le Claroffos 300 a été étudié par chronoélctrogravimétrie

Étude de l’effet d’un polyacrylate et d’un polyphosphate sur la morphologie et la minéralogie du sulfate de calcium

The retarding influence of polyacrylate and polyphosphate on the nucleation of calcium sulphate was investigated. SEM analyses show that these inhibitors didn’t only influence the nucleation kinetics but also the precipitate morphology by adsorption onto crystal growth sites. The influence of different concentrations of the additives on the mineralogy of solid precipitated was also examined. Spectroscopy Raman analyses showed that the calcium sulphate can precipitate under different phases, gypsum (CaSO$_4$.2H$_2$O), hemihydrate (CaSO$_4$.1/2H$_2$O) and / or anhydride (CaSO$_4$), as function of inhibitors concentrations

Experimental investigation on thermal performance of a PV/T-PCM (photovoltaic/thermal) system cooling with a PCM and nanofluid

In the present work, an experimental investigation is performed to assess the thermal and electrical performance of a photovoltaic solar panel cooling with multi-walled carbon nanotube&ndash;water/ethylene glycol (50:50) nano-suspension (MWCNT/WEG50). The prepared nanofluid was stabilized using an ultrasonic homogenizer together with the addition of 0.1vol% of nonylphenol ethoxylates at pH = 8.9. To reduce the heat loss and to improve the heat transfer rate between the coolant and the panel, a cooling jacket was designed and attached to the solar panel. It was also filled with multi-walled carbon nanotube&ndash;paraffin phase change material (PCM) and the cooling pipes were passed through the PCM. The MWCNT/WEG50 nanofluid was introduced into the pipes, while the nano-PCM was in the cooling jacket. The electrical and thermal power of the system and equivalent electrical&ndash;thermal power of the system was assessed at various local times and at different mass fractions of MWCNTs. Results showed that with an increase in the mass concentration of the coolant, the electricity and power production were promoted, while with an increase in the mass concentration of the nanofluid, the pumping power was augmented resulting in the decrease in the thermal&ndash;electrical equivalent power. It was identified that a MWCNT/WEG50 nano-suspension at 0.2wt% can represent the highest thermal and electrical performance of 292.1 W/m2. It was also identified that at 0.2wt%, ~45% of the electricity and 44% of the thermal power can be produced with a photovoltaic (PV) panel between 1:30 pm to 3:30 pm.</jats:p