30F-10 |
Simulation of microwave and fluidized-bed drying of particulate foods with a two-phase flow model |
H. FENG, Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, 382-F AESB MC 646, 1304 W Pennsylvania Ave, Urbana, IL 61801 Microwave drying can significantly reduce drying time and hence improve product quality. An inherent problem associated with microwave dryingis the non-uniformity of the heating. Combining microwave radiation with hot air fluidization provides an effective means of overcoming the non-uniform heating problem. This technique incorporates a fluidized bed into the microwave cavity. The fluidization provides a pneumatic agitation so that time-averaged microwave radiation can be received by a single food particle. An engineering study was conducted to simulate the process kinetics of a microwave and fluidized bed combined drying system and to lay a foundation for the design, scale-up, and operation of such a drying system. The purpose of this study is to simulate the process kinetics of microwave and hot air combined drying of particulate foods in a fluidized bed with two-phase flow equations. The drying problem is modeled as an air-solid flow in a vertical conduit with volumetric heat generation inside the particles. The hot air is described with a continuity equation, a momentum equation, and a total energy equation. The same set of equations is also derived for food particles. The mass transfer term in the equations is evaluated with a simplified diffusion equation. Microwave heat generation is described with an empirical equation. A finite difference program based mainly on the particle energy equation is developed to estimate particle drying. The model simulation is checked against the experimental results of diced apples. The model prediction for product moisture agrees well with the experimental result. Predicted product temperature is slightly lower than the measured. This may be caused by error in the estimation of the microwave power term. The development and validation of an air-particle model will provide a relatively simple means of simulating the drying kinetics of microwave and convective drying in a fluidized bed.
Session 30F, Food Engineering: Transport processes and kinetics
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