Atmospheric freeze-drying

Tq- inlet (ambient) temperature - freeze-drying temperature Tf - regeneration temperature T, - freezing temperature 

Assuming uniformly retreating ice front and using sorption isotherms for the solid adsorbent, Wolff and Gibert (1990b) proposed the following model for atmospheric freeze-drying in a fluidized bed of particulate adsorbent  

Derivation of Eqs. (21.1) through (21.3) along with simulation results for different process conditions are given by Wolff and Gibert (1990b). 

Because of the internally controlled mass transfer, drying times for atmospheric freeze-drying are longer than for the vacuum freeze-drying. The difference in drying time increases with particle size (thickness). Thus, for 5-mm-thick particles, about 2 hours are needed to reduce the moisture content from 4 kg/kg to 2 kg/kg in the vacuum process, whereas 6 hours are required 

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Di Matteo, P, Donsi, G. and Ferrari, G., The role of heat and mass transfer phenomena in atmospheric freeze-drying of foods in a fluidised bed, /. Food. Eng., 59 (2003) 267-275. 

Johnston, K.P. Williams, R.O. Enhanced aqueous dissolution of a poorly water soluble drug by novel particle 75. engineering technology spray-freezing into liquid with atmospheric freeze-drying. Pharm. Res. 2003, 20 (3),... 

Reyes, A., Vega, R.V., and Bruna, R.D., Effect of operating conditions in atmospheric freeze drying of carrot particles in a pulsed fluidized bed. Drying TechnoL, 28,1185-1192,2010. 

Rahman, S.M.A. and Mujumdar, A.S., A novel atmospheric freeze-drying system using a vibro-fluidized bed with adsorbent, Drying TechnoL, 26, 393-403, 2008. 

Wolff, E. and Gibert, H., Atmospheric freeze drying. Part 2. Modeling drying kinetics nsing adsorption isotherms. Drying TechnoL, 8(2), 405-428, 1990. 

Atmospheric freeze-drying of several foods, including mushrooms and carrots, was investigated in a fluidized bed of finely divided adsorbent that combined adsorption and fluidization, achieving improved heat and mass transfer and shorter drying time than vacuum drying [50,51]. Products could be dried economically using very simple equipment. 

K.E. Yassin and H. Gilbert, Atmospheric freeze-drying of foods in a fluidized bed of finely divided absorbent. In Proceedings of the Sixth International Congress on Food Science Technology, No. I, 1983, pp. 208-209. 

E. Wolff and H. Gibert, Atmospheric freeze-drying. Experimentation and modelisation. Proceedings of Sixth International Drying Symposium IDS 88, September 5-8, Versailles, France, M.A. Roques and A.S. Mujumdar (Eds.) Vol. l,p.OP411 (1988). 

Claussen IC, Ustad TS, Strommen I, Waide PM (2007) Atmospheric freeze drying—a review. Drying Technol 25 947-957... 

Figure 21.1 Process configuration for continuous atmospheric freeze-drying. (From Wolff and Gibert, 1990a.)...

Figure 21.4 Comparison between freeze-drying and atmospheric freeze-drying for...

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