17H-21 |
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F. Vegara-Balderas, B. U. Kozanoglu, E. Torres-Madrid, and J. WELTI-CHANES4. (1) Ingenieria Quimica y Alimentos, Universidad de las Americas-Puebla, Cholula, Puebla, 72820, Mexico Fluidized bed drying has booth theoretically and experimentally studied by many researchers. However the drying process, at relatively high temperatures or long residence times, may cause the partial degradation of thermolabile products in systems as foods. A fluidized bed operation under vacuum offers the possibility of eliminating these problems. With this last idea in mind a research work was developed to design and build a fluidization column to operate under vacuum conditions and to evaluate its functionality with small cubes of carrot. The column was made of glass with a inside diameter of 100 mm and height of 800 mm, it was fitted with a stainless-steel perforated distributor consisting of openings 1 mm in diameter, with a 3% free area and a calming section filled with Raschig rings located underneath. The air was heated by a system of electrical resistences and the vacuum conditions were achieved through a rotary vacuum pump. Several temperature and pressure measuring probes as well as a sampling point were integrated to the column. Tests with carrots cubes (5mm) were run a three distinct temperatures, 30, 40 and 50°C, and at atmospheric and vacuum pressure (10 mm Hg). Pressure drop in the bed was in the range of 0.5 to 0.8 kPa, consequently the variation of the air pressure along the bed was practically negligible as compared to the absolute pressure. Application of vacuum had an important effect to reduce the drying time for carrot, effect that is more important when the air temperature is reduced, a 50% reduction of drying time was reached at lower air temperatures and vacuum operations. Kinetic drying data were used to simulate the vacuum fluidized drying process using a transient mathematical model obtained good results. Quality of carrots, color and rehydration rates, was improved using vacuum conditions. Results seem to indicate that in the case of porous particles, like carrots cubes, a decrease in operating pressure enhances the drying process.
Session 17H, Food Engineering: Thermal processes
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