Effective Diffusivities and Energy Consumption of Whole Fruit Chinese Jujube (Zizyphus jujuba Miller) in Microwave Drying

Abstract

Microwave drying of whole fruit Chinese jujube was performed at 45, 90, and 135 W. Ten commonly used mathematical models of thin-layer drying were compared. The Midilli model was best in describing drying time dependency of product moisture ratios. The initial drying rate and drying rate constant are linearly proportional to microwave power level. An effective diffusivity model was presented and validated with the Renka-Cline algorithm. The model has very high predictive precision, suggested by the relative percentage error of 3.734% on average between the model and the Renka-Cline algorithm. The effective diffusivity was proved to be a linear function of microwave power level and a quadratic function of moisture content. Energy consumption in microwave drying of Chinese jujube decreased as microwave power increased from 45 to 135 W, but 90 W was adequate for high-quality products with less energy consumption.

Keywords:

• Effective diffusivity equation
• Energy consumption
• Renka-Cline algorithm
• Shrinkage
• Thin-layer drying

Notes

Note: The Midilli model is expressed as MR = aExp(−kt ⁿ ) + bt; here, a, k, n, and b are model constants; MR is moisture ratio. R ², χ², and PE are coefficient of determination, chi square, and percentage error, respectively.