body or may be only at the lower or upper portion of the ejection duct the two baffles 3 a and 3 b moreover may be reduced to two short segments at any portion of the ejection duct the two baffles 3 a and 3 b are preferably aligned one to the other and in the zone where they are present they divide the ejection duct in two zones 2 a and 2 b having semielliptical or semicircular section and decreasing extent from bottom to top in the case the baffles 3 a and 3 b reach the opening 2 they divide it in two openings 2 a and 2 b having semielliptical or semicircular section in the case the baffle 3 is spiral shaped it may be free to rotate around the central body 1 the fig2 a represents a top view of the nozzle according to the present invention having two baffles 3 a and 3 b connecting the solid central body 1 to the internal walls of the ejection duct said baffles dividing the opening 2 in two openings 2 a and 2 b having semielliptical or semicircular shape the fig2 b represents a section of the same nozzle at the basis plane wherein 1 is the solid central body 3 a and 3 b are the two baffles which connect it to the walls of the ejection duct and 2 c and 2 d are the two zones wherein the ejection duct is divided by said baffles the fig3 discloses a longitudinal section of the nozzle of the invention along the a a line of fig2 a the central body 1 is connected to the walls of.