Rice drying is a critical post-harvest process that ensures food security. Freshly harvested rice typically has a moisture content ranging from 22% to 30%. If not dried to below 14% in a timely manner, enhanced enzyme activity and mold growth can significantly degrade the quality of both the rice and the resulting rice products. As an efficient convective drying device, the deep bed dryer removes moisture through the synergistic effects of airflow, temperature, and relative humidity, making it one of the widely applied drying technologies today. However, a core issue remains: how to design the aeration system to ensure that the drying airflow uniformly penetrates the rice layer, avoiding localized over-drying or insufficient drying?
Diswandi Nurba from IPB University in Indonesia at al. systematically evaluated the performance of four aeration system designs through a combination of Computational Fluid Dynamics (CFD) simulations and AHP-TOPSIS multi-criteria decision analysis, providing a scientific answer to this problem. The study had been published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2024577).
Traditional aeration system designs for dryers often rely on empirical methods or single-parameter testing, making it difficult to comprehensively consider the influences of multidimensional factors such as airflow, pressure, temperature, and humidity. This study employed a “simulation + multi-criteria decision” approach: first, CFD technology was used to simulate four aeration system models (composed of two floor shapes—“conical” and “sloping”—and two air pipe formations—“rectangular” and “circular”), visually presenting the distributions of airflow velocity, pressure, temperature, and humidity within the drying chamber. Subsequently, the AHP-TOPSIS method was introduced, using the quantitative data obtained from CFD (such as airflow uniformity, pressure variation, and temperature and humidity fluctuations) as evaluation indicators. Through multi-dimensional weight analysis, the optimal design was comprehensively selected. This method not only avoids the one-sidedness of single indicators but also reduces experimental costs through computer simulations, providing a more efficient technical pathway for dryer design.
The research results indicated that among the four models, “Model 4”, which utilized a “sloping floor + circular pipe formation”, performed the best. CFD simulations revealed that the sloping floor design reduced airflow obstruction at the base of the dryer, allowing air to diffuse more freely before entering the rice layer. The circular pipe formation achieved a more uniform radial airflow distribution, avoiding the “airflow blind spots” often associated with rectangular pipes. The combination of these two features resulted in smaller fluctuations in airflow velocity and more uniform temperature and humidity distributions within the drying chamber. A 5-hour drying simulation showed that Model 4 achieved an average drying rate of 2.22% per hour, reducing the average moisture content of the rice to 13.9%, significantly outperforming the other models.
This study deeply integrates “visual simulation” with “multi-dimensional evaluation”. Traditional designs often lead to inconsistent rice quality due to “uneven airflow distribution”. The new method not only visually presents where the airflow is strong or weak but also uses mathematical models to comprehensively compare the advantages and disadvantages of different designs, providing clear directions for optimization.
In practical applications, the “sloping floor + circular pipe formation” aeration system design can enhance drying efficiency and reduce mold losses caused by localized under-drying. Moreover, by ensuring more uniform temperature and humidity control, it safeguards the quality of the rice—this is particularly important in tropical regions, where the high temperature and humidity environment necessitate that rice be dried within 12 to 24 hours post-harvest. Optimizing drying technology can help mitigate food loss.
DOI: 10.15302/J-FASE-2024577