Calculation of the Height of the Drying and Separation Chamber in a Fluidized (Spouted) Bed

This study is devoted to improving the drying process of paddy rice using microwave (electromagnetic) energy in a spouted bed. The main objective is to determine the optimal height of the drying and separation chamber based on theoretical analysis and experimental validation. The influence of key process parameters, including electromagnetic wave power density, grain moisture content, and temperature evolution, was investigated. Experimental results showed good agreement with theoretical predictions, indicating that the heating time of the grain layer is approximately 2.1 s, with a nearly uniform temperature increase rate. It was established that the grain temperature should not exceed 50°C in order to preserve its germination properties, which limits the heating duration under fixed-bed conditions. Furthermore, an increase in grain moisture content leads to higher heat capacity and enhanced absorption of electromagnetic energy (up to η ≈ 0.8), resulting in accelerated heating. Although the magnetron generates a power density of up to 80 W/m², the effective absorbed power by the grain was found to be approximately 16 W/m². The analysis also revealed that electromagnetic radiation intensity is the dominant factor influencing mass reduction, closely correlated with temperature rise. Based on the obtained results and the application of Duval’s approach, a theoretical framework is proposed for determining the rational height of the drying chamber, ensuring sufficient residence time for complete drying while preventing premature particle entrainment. The findings can be used for the design and optimization of efficient microwave-assisted grain drying systems.

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