A chemical vapor deposition reactor comprising: a central axis of symmetry a flow flange assembly having a top and a bottom located opposite to the top of the flow flange assembly, wherein the flow flange assembly comprises a main flange body and an upper flow guide comprising an adjacent wall, having an interior surface and an exterior surface located opposite to the interior surface, connected to the main flange body and located between the main flange body and a reaction chamber volume, wherein a first fluid gap is formed between the interior surface of the adjacent wall of the upper flow guide and the main flange body of the flow flange assembly; wherein the flow flange assembly has (a) a bottom end interior surface with a normal line that is parallel to the central axis of symmetry and (b) a top end interior surface with a normal line that is perpendicular to the central axis of symmetry; a flow injector connected to a top of the flow flange assembly; and, a wafer carrier located adjacent to the bottom of the flow flange assembly, wherein the exterior surface of the adjacent wall has a top end and a bottom end located opposite to the top end, wherein the top end of the exterior surface has a diameter that is less than a diameter of the bottom end of the exterior surface, wherein the central axis of symmetry traverses the flow flange assembly, the flow injector and the wafer carrier, wherein a second gap is provided between the exterior surface of the adjacent wall of the upper flow guide at an outermost diameter of the upper flow guide and an upper surface of the wafer carrier at an outermost diameter of the wafer carrier, wherein the second gap is at a minimum value compared to values for all the other vertical separations between the exterior surface of the adjacent wall and the upper surface of the wafer carrier, and further wherein the first gap contacts the interior surface of the adjacent wall and extends along the interior surface of the adjacent wall from an innermost diameter of the upper flow guide to an outermost diameter of the upper flow guide, wherein the curved cross-sectional profile of the exterior surface of the upper flow guide is continuously curvilinear from the top end of the exterior surface of the adjacent wall of the upper flow guide to the bottom end of the exterior surface of the adjacent wall of the upper flow guide. a central axis of symmetry a flow flange assembly having a top and a bottom located opposite to the top of the flow flange assembly, wherein the flow flange assembly comprises a main flange body and an upper flow guide comprising an adjacent wall, having an interior surface and an exterior surface located opposite to the interior surface, connected to the main flange body and located between the main flange body and a reaction chamber volume, wherein a first fluid gap is formed between the interior surface of the adjacent wall of the upper flow guide and the main flange body of the flow flange assembly; wherein the flow flange assembly has (a) a bottom end interior surface with a normal line that is parallel to the central axis of symmetry and (b) a top end interior surface with a normal line that is perpendicular to the central axis of symmetry; a flow injector connected to a top of the flow flange assembly; and, a wafer carrier located adjacent to the bottom of the flow flange assembly, wherein the exterior surface of the adjacent wall has a top end and a bottom end located opposite to the top end, wherein the top end of the exterior surface has a diameter that is less than a diameter of the bottom end of the exterior surface, wherein the central axis of symmetry traverses the flow flange assembly, the flow injector and the wafer carrier, wherein a second gap is provided between the exterior surface of the adjacent wall of the upper flow guide at an outermost diameter of the upper flow guide and an upper surface of the wafer carrier at an outermost diameter of the wafer carrier, wherein the second gap is at a minimum value compared to values for all the other vertical separations between the exterior surface of the adjacent wall and the upper surface of the wafer carrier, and further wherein the first gap contacts the interior surface of the adjacent wall and extends along the interior surface of the adjacent wall from an innermost diameter of the upper flow guide to an outermost diameter of the upper flow guide, wherein the curved cross-sectional profile of the exterior surface of the upper flow guide is continuously curvilinear from the top end of the exterior surface of the adjacent wall of the upper flow guide to the bottom end of the exterior surface of the adjacent wall of the upper flow guide.