The aim of the present study is to develop mathematical analysis of a film dryer or refractance type dryer that helps in design, operation, modification, evaluating drying time and rates, improving quality and increasing energy efficiency. Strawberries juice was used as an example of liquid foods. For justifying this purpose a pilot plant refractance window dryer was designed. A film of juice with an initial thickness of approximately 3 mm, was applied on a hot glass plate heated by water underneath, that continuously contacts it. Nine experiments were conducted, namely: three variable flow rates per unit surface area of the dryer, 0.25, 0.21 and 0.18 m 3 /m 2 .s , and also three different levels of heating rates for each flow rate were also applied, i.e. 15.2 , 24.3 and 36.6kW/m 2 respectively. Liquid strawberries drying time ranged between 0.77-0.90 h compared to 5 h for traditional hot-air dryer at 60 o C .The model is reasonably accepted for predicting the drying coefficient-elapsed time product and moisture ratio with coefficients of determination of 97%.
The use of microwave energy is of growing interest due to brief time, volumetric heating due to its penetration and reduced processing time, making it an attractive source of thermal energy. The main objective of the present work is to study the effect of milk and tomato, strawberries juices temperatures and moisture contents, dry basis, on dielectric constant, loss tangent, loss factor and penetration depth at 2450 MHz affecting heat and mass transfer by microwave. It was found that the dielectric constant increased by increasing moisture contents, temperatures and increasing the ability of material to store energy. Dielectric constant and dielectric loss factor are exponentially satisfied with coefficients of determinations between0.84-0.91 for tomato and strawberries. The dielectric constant of milk satisfied a linear form with coefficients of determinations between 0.88-0.97. The loss tangent is deceased with increasing the moisture content indicating the energy lost or dissipated by the material, and satisfied a power form with coefficients of determinations ranged between0.75-0.98 for all tested materials. INTRODUCTION he ASAE (1994) reported that the dependence of dielectric properties of gains and seeds on temperature is not well documented, and the only information included shelled corn. Theraja (1993) reported that every medium is supposed to posses absolute and relative pemittivity. He added that for measuring relative pemittivity, vacuum or free space is chosen as the reference medium. It is allotted an absolute pemittivity of 8.854x10 -12 farad/m. Karmas (1980) mentioned that the variation of dielectric constant of moisture containing materials is approximately linear over a limited range from low to above 30% moisture content at room temperature. He stated that the dielectric
This study was carried out to evaluate some physical properties for two different varieties of peanuts, namely: Ismailia1 "Is1" and Giza5 "G5"such as length, width, shell thickness, weight, volume, percentage of void space, and density for kernels and Hulls. Hulled peanuts and kernels can be classified into three classes i.e. small, medium and large based on average values of their characteristics and associated standard deviation. Several empirical equations based on a large number of measurements for volume of an individual hull and kernel, bulk density are presented. The main objective of the present study is to evaluate some physical properties of two different Egyptian verities that affect design and development of; precision planting, grading, drying, fraying and storage machines.
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