Multivented twin-screw extruder

In a gaseous phase disengaging apparatus for a liquid phase process material having process material entrance and discharge ends, a housing provided with a pair of overlapping cylindrical axially parallel bores each provided with substantially identical co-rotating helical screws advancing said process material toward said discharge end, said helical screws being in relatively close clearance with said bores for the full transverse extent of said bores except in the region where said bores overlap, throughout which overlap region said screws interact in individual screw tip to peripheral expanse proximity, liquid phase raw process material inlet port opening sequentially into each screw channel of said apparatus and axially spaced outside and intermediate gaseous phase vent ports of radius R.sub.v opening internally into continuous communication with each apparatus material advancing passage, the axis of said outside vent ports being disposed inwardly of the housing bores by an amount a such that R.sub.v .ltoreq. a, the center-to-center axial spacing S.sub.v between said outside ports expressed in terms of t = lead of screw, R.sub.s = outside radius of screw, R.sub.v = radius of said vent ports, n.sub.T = number of tips and .gamma.= the outward angular inclination of said vent ports from normality with respect to the plane including the axes of said screws, being such that S.sub.v = t/2 (2 - 3/n.sub.T) + (t/.pi.) cos.sup.-1 (1 - a/R.sub.s) - (.gamma.t/.pi.) whereas said intermediate vent ports are axially disposed at approximately equal intermediate spacings between said outside vent ports.