The collection efficiency of a new helicoidal rotary demister, a novel technology for removing persistent fine droplets from gases, was evaluated using a tracer-based method. The demister uses a helicoidal element, which consists of a metal sheet wound as a spiral, designed to rotate at high speed within a cyclone body. Larger droplets are separated as they enter the cyclone housing, while the smaller droplets are carried by the gas into the helicoidal path of the rotating element, where they are centrifuged towards the outer collecting walls and, due to a baffle, flow counter-currently to the gas and are drained out from the bottom of the helicoidal element. The mist-free gas leaves through a channel located at the center of the spiral. The droplets collection efficiency and the pressure drop of the demister were measured under various conditions, to determine the impact of rotation speed and of gas flow rate. (C) 2010 Elsevier B.V. All rights reserved.