A cold plate apparatus that has an outlet plenum leading to an outlet opening includes an outlet transition that connects the outlet opening to the outlet plenum. The outlet transition defines a smoothly curving flow path from a direction along a long dimension of the outlet plenum, which is parallel to a plane defined by the outlet opening, to a direction along a centerline of the outlet opening, which is at an angle from the plane defined by the outlet opening. The outlet transition provides a smooth variation of cross-sectional area from the outlet plenum to the outlet opening.