Experiments were conducted to investigate the effect of different operating conditions on the process of wall deposition in a Buchi B290 pharmaceutical-type spray dryer, with a drying chamber diameter of 0.155 m and a main chamber height of 0.48 m. In the experiments, liquid flow rates were between 7 and 28 mL/min, airflow rates to the atomizer were between 170 and 670 L/hr, and main airflow rates through the dryer were between 20 and 38 m(3)/hr. The results suggested that the droplet concentration is more important than the initial droplet velocity in determining the rates of collision with walls. The collision of cold water droplets was simulated using a mathematical model based on tracking droplet trajectories, and the simulations of the deposition behavior give important guidance in interpreting the deposition mechanisms in the experimental results.