Flowrate quantification of the pumped-air stream from a 63 mm diameter centrifugal wheel atomiser

The air-pumping characteristic of a 63 mm diam centrifugal atomiser running dry within a cocurrent spray dryer was studied extensively using a novel e xperimental technique which involved the direct measurement of the wheel va cuum pressure together with the power required to pump the air. Approximate ly 10% of the power consumed by the atomiser was utilised in pumping the ai rstream. A further 25% was consumed in shearing the air around the wheel an d the remaining 65% was consumed by friction and motor losses within the dr ive train. Typically. the wheels considered pumped between 2 l s(-1) and 6. 5 l s(-1) of air at a maximum rotational speed of 50 000 rpm which correspo nded to between 5% and 16% of the primary air supply to the dryer. A dynami c closure of the wheel/atomiser body gap was observed occurring at 30 000 r pm to 40 000 rpm which was thought to be due to an upward acting force gene rated by the pressure differential either side of the wheel. This significa ntly affected the air-pumping behaviour of the wheel. (C) 1999 Elsevier Sci ence S.A. All rights reserved.