A mixing device for mounting between two catalyst beds in a multi-bed down-flow catalytic reactor, wherein said mixing device comprises: a. a circular top wall; b. a circular bottom wall essentially parallel to the top wall and comprising a circular centrally located outlet opening; c. a cylindrical divider wall between said top wall and said bottom wall in fluid tight contact with said top and said bottom wall and wherein said divider wall has at least one opening that extends from the bottom of the divider wall to less than the full height of the divider wall; d. at least one inlet passageway for fluid wherein said inlet passageway is formed by the outer surface of the divider wall, the divider wall opening, a curved side wall abutting the outer surface of the divider wall and encompassing the divider wall opening and wherein the sidewall is connected to the divider wall in fluid tight contact and wherein said side wall extends less than the full height of the divider wall, and a capping top portion in fluid tight contact with the top of the side wall and the outer surface of the divider wall wherein the capping top portion is level with the top of the divider wall opening to form the at least one inlet passageway and wherein said inlet passageway is of greater radius, as measured from the center of the outlet opening to the side wall, at the inlet passageway opening than at the sidewall divider wall opening to form a constricted passageway to thereby impart an arcuate flow to the fluid; wherein "essentially parallel" means the top and bottom walls are within 5 degrees of being coplanar; and at least one cylindrical riser wall wherein the riser wall surrounds the outlet opening and wherein the radius of the riser wall, as measured from the center of the outlet opening to the interior surface of the riser wall, is less than the radius of the divider wall, as measured from the center of the outlet opening to the interior surface of the divider wall, and wherein the riser wall is in fluid tight connection with the bottom wall but does not extend to the full height of the divider wall. a. a circular top wall; b. a circular bottom wall essentially parallel to the top wall and comprising a circular centrally located outlet opening; c. a cylindrical divider wall between said top wall and said bottom wall in fluid tight contact with said top and said bottom wall and wherein said divider wall has at least one opening that extends from the bottom of the divider wall to less than the full height of the divider wall; d. at least one inlet passageway for fluid wherein said inlet passageway is formed by the outer surface of the divider wall, the divider wall opening, a curved side wall abutting the outer surface of the divider wall and encompassing the divider wall opening and wherein the sidewall is connected to the divider wall in fluid tight contact and wherein said side wall extends less than the full height of the divider wall, and a capping top portion in fluid tight contact with the top of the side wall and the outer surface of the divider wall wherein the capping top portion is level with the top of the divider wall opening to form the at least one inlet passageway and wherein said inlet passageway is of greater radius, as measured from the center of the outlet opening to the side wall, at the inlet passageway opening than at the sidewall divider wall opening to form a constricted passageway to thereby impart an arcuate flow to the fluid; wherein "essentially parallel" means the top and bottom walls are within 5 degrees of being coplanar; and