98 mixing efficiency when the tube diameters is 0 55 inch and the orifice diameters is 0 185 inch the pressure drop between the entrance to the mixer tubes and the inlet end of the catalyst bed is kept at 0 334 inches water and the pressure drop between the manifold and the interior of the transfer tubes is kept at 0 418 inches water a mixer assembly having twenty transfer tubes with four orifices in each tube is able to achieve a 97 mixing efficiency when the tube diameters is 0 364 inch and the orifice diameters is 0 104 inch the pressure drop between the entrance to the mixer tubes and the inlet end of the catalyst bed is kept at 1 75 inches water and the pressure drop between the manifold and the interior of the transfer tubes is kept at 3 74 inches water a mixer assembly having twenty transfer tubes with four orifices in each tube is able to achieve a 97 mixing efficiency when the tube diameters is 0 364 inch and the orifice diameters is 0 104 inch the pressure drop between the entrance to the mixer tubes and the inlet end of the catalyst bed is kept at 0 37 inches water and the pressure drop between the manifold and the interior of the transfer tubes is kept at 0 76 inches water a mixer assembly having twelve transfer tubes with five orifices in each tube is able to achieve.