(666f) Air Pressure Effects on Powder Flow Rate for Hopper Discharge

This paper presents flow rate measurements using a purpose built critical orifice apparatus where discharge occurs into a closed chamber where the air pressure is controlled. Results using four pharmaceutical excipients show that the flow rate can be increased several times by lowering the atmospheric pressure by an amount as little as a few hundred Pa at discharge. This paper presents in detail the experiments and dimensional analysis which was carried out to obtain a general relationship between the flow rate and the applied vacuum. The potential impact of the experimental results and the proposed dimensional model is significant for the design of die fill operations on tablet presses and other powder dosing processes.