A gas blower device for blowing gas onto a surface of a traveling strip includes a plenum in the form of a hollow box for containing gas and comprising two side surfaces, a back surface and a front surface opposite to the back surface. The front surface having a profile of convex type symmetry with respect to a mid-plane perpendicular to the plane of the strip, so that a middle ridge of the front surface is located at the smallest distance from the plane of the strip. The front surface further presenting multiple tubular nozzles protruding at the front surface and having a gas outlet orifice facing in use the traveling strip. All the outlet orifices are essentially in a plane parallel to the strip plane. The gas blower device further includes a gas intake tube for feeding the plenum with gas.