We proposed a micro-pin-fin based membrane separator. An enclosed membrane with micron scale holes was symmetrically populated in a rectangular duct. When gas phase interacts with the membrane, the gas-liquid interface cannot break through the pin-fin holes due to the increased surface energy. A two-dimensional numerical model simulated the separation process. The volume of fluid (VOF) method tracked the gas-liquid interface. Multiscale grids were used. When a bubble attacks the pin-fin membrane, strong liquid circulation occurs at the membrane entrance. Pressures in the side region are larger than those in the core region. Liquid plugs are shortened due to the pressure driven flow from side region to core region to cause the bubble coalescence. The separation length was shortened while increasing the gas flow rates. The bubble lengths were weakly influenced by gas flow rates. Liquid plugs are quickly shortened following the membrane entrance. The frictional pressure drop of the two-phase mixture in the side region was larger than that of liquids in the core region, even at low gas flow rates. The ultra large gas flow rates yielded quite large bubble pressure to exceed the capillary pressure limit, causing the separator failure. Ultra-low and large gas flow rates specified the separator operation range. (C) 2015 Elsevier Ltd. All rights reserved.