Computational fluid dynamics and analytical modeling for predicting effects of airflow temperature and relative humidity on the terminal velocity of agricultural granular materials

This study proposes a methodology based on computational fluid dynamics (CFD) for predicting the terminal velocity of agricultural granular materials in different airflow conditions that eliminates the need for extensive experiments. Terminal velocities of three seeds, namely chickpea, lentil, and rice, representing spherical, disc, and cylindrical seed shapes, respectively, were measured as a function of airflow temperature and relative humidity (RH) in an open‐circuit vertical wind tunnel. Experiments were carried out using a 3 × 3 factorial design in three replications. Terminal velocities of lentil and rice seeds varied from 4.73 to 5.67 m/s and 4.1 to 4.67 m/s, respectively, at 15–25°C and 20–80% RH. For chickpea seeds, terminal velocities varied from 8.8 to 9.43 m/s at 26–39°C and 20–60% RH. The effects of airflow temperature and RH on the terminal velocity of grains were significant at the 1% level. For all three grains, terminal velocity increased with temperature and RH. CFD‐predicted and theoretically calculated values of terminal velocity were compared with experimental results. Results of the statistical analysis showed that terminal velocities of lentil and chickpea calculated using analytical models were significantly higher than those obtained experimentally, whereas they were lower for rice seeds at the 5% level. The terminal velocity obtained through CFD simulations was in close agreement with the experimental results at the 1% level for lentil, chickpea, and rice seed at 5% level. PRACTICAL APPLICATIONS: One of the impressive factors of optimizing the loss of harvesting of cereals is the terminal velocity and its variation regarding the ambient conditions. Computational fluid dynamics is a validated method that can simulate the phenomenon and help us with a prediction of some characteristics. The results can be a basis for doing so in simulating the transfer of granular material in food processing devices.