Numerical model to study the statistics of whole milk spray drying

Abstract

Using a numerical model, this study investigates the spray drying process of whole milk by providing statistics on droplet conditions at exit and first impact with the surfaces of the chamber. A comprehensive four-stage droplet evaporation model was validated against an experiment and then coupled to an Euler–Lagrange model for simulating the milk droplet trajectories inside a dryer. Results show that larger droplets remain for a shorter time in the chamber and contain more moisture on exiting. Higher injection angles result in longer residence times, which leads to lower moisture content for the droplets. By increasing the injection velocity of droplets, their relative velocity compared to the airflow increases, raising the rate of evaporation, and consequently more droplets exit the chamber as fully dried. Furthermore, decreasing the airflow rate and humidity, as well as increasing the airflow inlet temperature, results in a lower moisture content in the final powder. When the droplets impacted the wall of the chamber for the first time, nearly 67% of them were fully dried, and 55% had a velocity magnitude less than 1 m/s. A considerable portion of droplets (close to 52%) impacted the wall at an angle of less than 8°. • A modelling approach to better understand the drying of milk droplets in spray dryers is presented. • This approach includes modelling the flow, particle tracking, and a comprehensive drying model. • The validate drying model captures temperature and moisture content distribution. • This model is then used to extract statistical information about the drying state of milk droplet. • The statistical study provides insight into the effects of key operating parameters.