(263b) CFD-Dpm Simulations of Spray Drying Process: Drying Kinetics of Individual Droplets in Water Droplet Group

Spray drying processes have played considerably essential roles in several industries, such as pharmaceutical, food, ceramic, and others. However, many factors affect the physical properties of dry particles, and the detailed mechanism of dry particle generation is not sufficiently clarified. Therefore, the operating conditions are determined by trial and error to obtain the desired product. A look at the work published so far reveals the existence of maps of velocity, temperature, humidity, and pressure within spray dryers obtained using computational fluid dynamics; CFD. However, the drying kinetics of individual droplets and their subsequent change in diameter as their trajectories are still missing.

In this study, we performed CFD-DPM simulations of droplet drying in a mini spray dryer. The developed model and calculation results were validated based on mini spray drying tower experiments. We focused on the drying behavior in the droplet group and investigated the changes in the droplet diameter and the driving force of evaporation. The results of the numerical simulation revealed that the driving force of evaporation, ΔT, changed every moment as the droplets traveled through different temperature distribution fields in the drying tower. Therefore, each droplet has different drying kinetics in the spray dryer. Also, it was suggested that the prediction of the drying kinetics of the droplet group was insufficient under the assumption of the steady condition, and the influence of the surrounding droplets should be considered.

Furthermore, we investigated the effects of operating conditions of the spray drying process (such as air temperature, airflow rate, liquid feed rate, and droplet diameter) on the drying kinetics of the droplet group. The numerical simulations were performed under various conditions to calculate the drying kinetics of the droplet group in the spray dry process. The calculated results revealed that the drying kinetics of the droplet group strongly depended on the driving force for the droplet evaporation(∆T). Finally, we proposed a method to estimate the drying kinetics of the droplet group from the operating conditions by organizing with the thermal efficiency and Nusselt number.