Quasi-steady state thermal performances of a solar air heater with two absorber

Quasi-steady state thermal performance of a solar air heater with a combined absorber is studied. The whole energy balance equations related to the system were articulated as a linear system of temperature equations. Solutions to this linear system were assessed from program based on an iterative process. The mean temperature variation with time and the thermal performance parameters were deduced from simulation outputs. Simulations were performed for typical days of the twelve months of the year. Results show maximum values of mean temperatures at solar noon ranging between: 78°C and 87°C for the cover, 102°C and 114 °C for the absorber 61°C to 67°C. Experimental and simulated results correlate well for hours before solar noon (with R²≈0.988) and show some discrepancies for hours after solar noon. These differences were related to the neglect of heat capacity effects in the model. Experimental and calculated solar heater efficiencies at solar noon approached respectively about 62 and 61%. The removal factor FR and the efficiency factor F’ calculated were respectively 0.4 and 0.33, whereas the values assessed from experiments were respectively 0.79 and 0.63. This model allowed predicting the collector performances and is more suitable for hours before solar noon.Keywords: Quasi-steady state, solar air heater, combined absorber, modeling, experimen

A comparative study of direct and indirect solar drying of mango

In this work, direct and indirect solar drying parameters of two mango varieties were estimated and compared using direct and indirect solar dryers under the same meteorological conditions. For both drying methods, drying curves were established and fitted using 10 semi-empirical models, drying rate and drying efficiency curves weredetermined, effective water diffusivity was estimated and quality of dry slice was evaluated. Results showed that in indirect solar drying, the tray position in the dryer did not have an influence on drying curves whereas in direct solar drying this influence was very significant. Indirect solar drying curves were suitably fitted by Approximation diffusion model (with R2. 0.99, RMSE.0.0387, E<12 % and c2<10-5) while direct drying curves were best fitted by Verma and al. and Approximation diffusion models (with R2.0.99, RMSE<0.0276, E<12 % and c2<10-3). Indirect solar dryingoffered highest drying rates and water diffusivities. Its diffusivities increased with the number of drying days between 1.5 x10-10 and 2 x10-10 m2/s whereas those of direct solar drying decreased with the drying days number between 5 x10-11 and 1.85 x10-10 m2/s. With efficiency from 2 to 48 % indirect solar drying was found to be more effective thandirect solar drying with efficiency from 0 to 34 %. Indirect solar drying with an average final water content of 16.6 % (dry basis) and a final water activity of 0.57 was then the most efficient, but also the most expensive. Thus, indirect solar dryer was found to be suitable for industrial or semi industrial mango drying, whereas direct solar dryer was appropriate to a family scale traditional mango drying

Drying parameters influence on ‘Ameclyae’ Opuntia ficus prickly pear oil quality

[EN] The aim of this work is to study the effects of drying conditions on the quality of extracted pricly pear seed oil, specifically α-tocopherol content. Drying experiments were carried on following a full 23 factorial design using a vertical drying tunnel. The temperature range was 45 to 70°C, relative humidity range was 15 - 30% and air velocity was 1 and 2 m/s. The Midilli-Kucuk model was found with satisfaction describing the seed air drying curves with a correlation coefficient of 0.999 and a standard error of 0.01. For each drying condition, the extraction of fixed oil seeds was performed at cold using mechanical pressing method. The oil quality was evaluated on the basis of the a-tocopherol content. The a-tocopherol was identified and quantified by high-performance liquid chromatography (HPLC-UV). According to the experimental results, it was found that convective drying of thin layer of seeds at soft air conditions, drying temperature of 45°C, relative humidity of 15% and air velocity of 1m/s give the optimal quality of extracted oil in terms of a-tocopherol content.Hassini, L.; Desmorieux, H. (2018). Drying parameters influence on ‘Ameclyae’ Opuntia ficus prickly pear oil quality. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 115-122. https://doi.org/10.4995/IDS2018.2018.7861OCS11512

Prise en compte de l’environnement dans le transfert de technologie. Cas des séchoirs

Leséchage est un procédé de conservation utilisé depuis longtemps en Afrique car adapté aux techniques et énergies disponibles localement. Cependant l’importance des séchoirs proposés comparé à ceux utilisés montrent que les critères de construction et d’énergie ne suffisent pas à en garantir l’utilisation durable. A l’aide du modèle STOU, il est montré que le système dans lequel évolue le produit sec doit être pris en compte pour éviter les échecs de transfert des technologies. La méthode de conception distribuée permet de prendre en compte l’environnement. Son application a permis la conception d’un séchoir de mangues; la simulation de son fonctionnement montre qu’il permet d’obtenir une qualité plushomogène de mangues sèches. Aussi les liens entre les acteurs du système environnant doivent être identifiés : Caractériser ces différents systèmes et liens permet de proposer des séchoirs plus adaptés à la fois à l’environnement mais aussi répondant mieux à l’utilisation prévue du produit sec. Ainsi, l’identification des réseaux d’acteurs du séchoir a spiruline au Tchad met en évidence 4 types de réseau et donc de séchoir en fonction de l’utilisation de la spiruline Drying is used and well-known as food preservation process. But energy and build criteria are not sufficient to guaranty a long use of a designed dryer. The use of the STOU model allows the necessity of the taking into account of the environmental system to be pointed out. The design method is used because it considers that environment. Its applicationallowed the design of a dryer for mangoes. The simulation of the dryer running shows that such a dryer gives a better quality of the final dry product. The links between the actors in the system are identified. That allows the design of the dryer to be in a better accordance to the need. In the case of the Spirulina transformation in Chad, the identification of the actor networks allows to differentiate 4 networks depending on the dry Spirulina use

Caractérisation du séchage convectif de la variété de mangue Amélie

Dans cette étude, une caractérisation du séchage convectif de la variété de mangue « Amélie » est réalisée à travers l’établissement des cinétiques de séchage de 50°C à 70°C et de l’isotherme de désorption à 40°C. La diffusivité effective est identifiée et varie de 0,75x10-9m².s-1 à 50°C, à 1,07x10-9m².s-1 à 60°C et 1,29x10-9m².s-1 à 70°C. L’énergied’activation déterminée à partir de données expérimentales est de l’ordre de 25 kJ/mole. Parmi les modèles semi-empiriques de cinétique de séchage et d’isotherme de désorption, le modèle de Page, avec un coefficient de corrélation supérieur à 0,99, s'est avéré le meilleur modèle pour décrire les courbes de séchage de l’ «Amélie », tandis que les modèles d’Henderson modifié, de GAB et de Peleg ajustent  convenablement l’isotherme à 40°C de cette variété de mangue. La teneur en eau correspondant à l’activité de l’eau de conservation 0,6 est évaluée à 15,31% (base sèche) et la teneur en eau en monocouche d’eau identifiée à partir du modèle de GAB est de 10,5 % (base sèche). In this study, a characterization of the convective drying of « Amélie » mango variety is carried out through the establishment of drying kinetics from 50°C to 70°C and of the desorption isotherm at 40°C. The effective diffusivity is identified and varies from 0.75x10-9m².s-1 at 50°C, to 1.07x10-9m².s-1 at 60°C and 1.29x10-9m².s-1at 70°C. The activationenergy determined from experimental data is about 25kJ/mole. Among semi-empirical models of drying kinetics and desorption isotherm, the Page model, with a correlation coefficient higher than 0.99, was found to be the best model to describe " Amélie " drying curves, while Modified Henderson, GAB and Peleg models suitably fitted the desorption isothermat 40°C of this mango variety. The moisture content corresponding to 0.6 water activity of conservation is evaluated at 15.31% (dry basis) and the mono-layer water content identified from the GAB model is X m=10,5% (dry basis)

Profils des teneurs en eau de la patate douce durant son séchage convectif

International audienc