Power-dependent modeling of moisture transport and energy performance during microwave drying of pharmaceutical wet granules

Abstract

This study provided a comprehensive modeling framework for microwave drying of pharmaceutical wet granules using 30, 45, 60, 75, and 90 W. The study assessed key drying process parameters, including moisture-removal kinetics, drying efficiency, specific energy consumption, effective moisture diffusivity, and apparent microwave activation energy. Increasing microwave power from 30 to 90 W reduced the time required to achieve 90 % moisture removal from 2,117 to 498 s, respectively. At this common endpoint of moisture removal, the 90 W condition achieved the highest cumulative drying efficiency (11.33 %) and the lowest cumulative specific energy consumption (19.92 MJ/kg). Furthermore, effective moisture diffusivity increased from approximately 6.09 × 10 ⁻⁹ to 34.61 × 10 ⁻⁹  m ² /s, and the apparent microwave activation energy was 15.23 W/g. The Weibull model well described the moisture-removal performance, and its parameters correlated with microwave power. In addition, empirical models were developed to estimate cumulative drying efficiency and specific energy consumption as simultaneous functions of power and drying time. This finding indicated a non-monotonic relationship between microwave power and energy performance; specifically, enhanced power improves overall performance only when the decrease in drying time offsets the rise in instantaneous energy input. This proposed framework provides a quantitative basis for evaluating various microwave-drying conditions and helps identify appropriate operating regions within the examined spectrum.