The specific aims of the research are to define the inter-relationships among heat and mass transfer and the collection of particulates and fluid properties, flow rates, system geometry, particle properties, etc. for the following systems: (1) contact with liquid drops under circumstances which promote circulation within the drops; (2) contact with liquid in the form of froth; and (3) contact with wetted surfaces in geometries which provide strong secondary flow patterns in the gas. It was found that both transport rates and particulate collection might be increased considerably by employing a scrubber especially designed to promote the mechanism of drop oscillation. All of the research is based on thesis investigations on: (1) liquid drops with internal circulation; (2) baffled conduits; (3) froth systems; and (4) automatic control. Details of these several investigations are given with charts and references included.