RESUMEN
This investigation explores the effectiveness of hot air-drying and ambient ventilation techniques in enhancing the storage quality of Khao Dok Mali 105 paddy rice within small-scale barns in Northeast Thailand. Through comprehensive analysis of moisture and temperature dynamics, the research revealed that an optimized main air pipe system significantly reduces moisture content from 25% db to a desirable 16% db, outperforming alternative systems. Spatial assessments within the barn highlighted the importance of placement, showing that front sections achieved lower moisture levels. This underscores the need for uniform moisture distribution and temperature management to prevent quality degradation. Notably, after 84 h of drying, variations in moisture content across different barn locations emphasized the critical role of environmental control. These insights pave the way for advancing grain storage practices, focusing on strategic ventilation and environmental monitoring to ensure rice quality over time. This study not only challenges traditional methods but also offers significant practical implications for optimizing small-scale rice storage, providing a pathway towards sustainable post-harvest processing in resource-constrained environments.
RESUMEN
This research introduced an energy-efficient drying method combining hot-air drying with stepwise microwave heating for producing quick-cooking red beans. Crucial parameters such as the effective diffusivity coefficient (De), and specific energy consumption (SEC) were examined across varying conditions with the aim of optimizing the drying condition. The results showed that De and SEC varied in a range of 0.53 × 10-9-3.18 × 10-9 m2·s-1 and 16.58-68.06 MJ·(kg·h-1)-1, respectively. The findings from the response surface methodology indicated that optimal drying conditions for cooked red beans are achieved at a hot air temperature of 90 °C, a microwave power of 450 W (corresponding to an initial intensity of 2.25 W·g-1), and a rotational speed of 0.2 Hz. These conditions lead to the maximum effective diffusivity coefficient and the lowest specific energy consumption. Further investigations into step-up (150-300 W to 300-450 W) and step-down (300-450 W to 150-300 W) microwave heating modes were conducted to refine the drying process for enhanced energy efficiency. The synthetic evaluation index revealed that step-down microwave heating strategies of 450 W-to-150 W and 300 W-to-150 W, applied at a temperature of 90 °C and a rotational speed of 0.2 Hz, were notably effective. These methods successfully minimized energy use while preserving the quality attributes of the final product, which were comparable to those of traditionally cooked and freeze-dried red beans. The combined approach of hot-air drying with step-down microwave heating presents a promising, energy-saving technique for producing quick-cooking beans that retain their rehydration qualities and texture.
RESUMEN
Stepwise drying is an effective technique that promotes energy saving without additional capital cost. The stepwise drying mode was investigated for energy consumption and dried product qualities using a coupled heat and mass transfer model associated with kinetics equations of volume shrinkage and degradation of ß-carotene in carrot cubes. Simulations were performed using a finite element method with extension of a chemical species transport. Validation experiments were carried out under constant drying modes at 60 °C, 70 °C and 80 °C using a lab-scale convective hot air dryer. The verified models were subsequently employed to investigate the effects of two step-up drying modes (60 to 70 °C and 60 to -80 °C). The optimal drying condition was determined using the synthetic evaluation index (SI) with criteria of high specific moisture evaporation rate (SMER), low shrinkage ratio and ß-carotene degradation. Simulated results showed comparable agreement with experimental data of moisture content, shrinkage ratio and ß-carotene ratio. Step-up drying of 60 to 70 °C gave the highest SMER of 0.50 × 10-3 kg of water evaporated per kWh, while the operation at constant temperature of 80 °C gave the lowest value of 0.19 × 10-3 kg of water evaporated per kWh. Model-predicted results showed less shrinkage of carrot cubes, but higher degradation of ß-carotene under step-up drying compared to single-stage drying under temperature of 60 °C. Based on the highest SI value (0.36), carrot cubes were optimally dried under step-up mode of 60 to 70 °C.
