Showing papers by "Mohammed Farid published in 2002"

Microwave vacuum drying of banana slices

Abstract: Vacuum drying of banana slices was studied in a domestic microwave oven. The results show that banana temperature rises uniformly and rapidly to the saturation water vapor temperature corresponding to the vacuum used then rises slowly until most of the free moisture is lost. The thermal and drying efficiencies were found to drop from almost 100% at the beginning of the drying (high moisture content) to as low as 40% and 30% respectively at the end of drying. Both efficiencies were found to increase with the use of vacuum, especially at low moisture content.

The moving boundary problems from melting and freezing to drying and frying of food

Abstract: It was possible to describe large number of processes such as melting, solidification, microwave thawing, spray-drying, and freeze-drying by a single theoretical model. All these applications and some others have one thing in common, that is the formation of a moving interface during the process of heat and mass transfer. This interface may be defined by a sharp boundary or by a region, depending on the application considered. The unsteady-state heat conduction equation was found to describe well the transport of heat in these processes. Two different numerical solutions have been developed, one for the sharp interface and the other for materials that undergo phase transformation within a range of temperatures. In spite of the large variation in the applications considered in this paper, the agreement was good between the theoretical predictions and our experiments, and some of the measurements available in the literatures.

A simple and effective model for cross-flow microfiltration and ultrafiltration

Abstract: A semi-theoretical unsteady-state model for the flux in cross-flow microfiltration and ultrafiltration has been developed. The model predicts fouling behaviour for a wide range of particle sizes and foulant concentrations. The developed model uses only two coefficients, k1 and k2, incorporating both the influences of the cake formation and the shear cleaning of the membrane, to describe flux decline. These two parameters were found to be almost independent of the operating conditions. The model provides both a fundamental understanding of the key physical phenomena governing flux decline and a rational basis for the design of an improved and modified cross flow filters. Un modele semi-theorique a l'etat non permanent a ete mis au point pour les ecoulements en microfiltration tangentielle et en ultrafiltration. Le modele predit le comportement d'encrassement pour une large gamme de tailles de particules et de concentrations des salissures. Ce modele emploie seulement deux coefficients, k1 et k2, incorporant les influences de la formation du gateau et le nettoyage par cisaillement de la membrane, afin de decrire le declin du flux. Ces deux parametres s'averent quasi independants des conditions operatoires. Le modele permet une comprehension fondamentale des principaux phenomenes physiques qui gouvernent le declin du flux et fournit une base rationnelle en vue de la conception de filtres tangentiels ameliores et modifies.