Numerical analysis of drying characteristics of frozen material immersed in fluidized bed at low temperature under reduced pressure

A spherical frozen material was dried in a fluidized bed of inert particles at a low temperature (lower than the melting point of water) under reduced pressure. To evaluate the drying characteristics of the frozen material, the heat and mass transfers in the material during the drying process were calculated using one-dimensional differential equations. The fitting parameters (accommodation coefficient of internal sublimation and heat transfer coefficient at the surface of the material) were determined to fit the calculation results and the experimental data. Drying characteristics, such as the distributions of moisture content and temperature in the material during drying, were calculated. Operational conditions, such as bed temperature, humidity, and heat transfer coefficient (gas velocity) at the surface of the material were varied in the calculation, and the effects on the end time of drying were estimated. Sublimation in the interior of the material governs the drying characteristics. The dry region in the material became resistant to heat transfer. The calculation results are reasonable for expressing the drying characteristics of freezedrying, that is, our calculation method can be used to estimate the drying characteristics of frozen material in a fluidized bed.(c) 2022 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved.

Automated summary

This study examines the drying characteristics of a spherical frozen material using a fluidized bed drying method. The heat and mass transfers during the drying process were calculated using one-dimensional differential equations. The results indicate that sublimation within the material governs the drying characteristics, and the dry region within the material exhibits resistance to heat transfer.