A tray for use in a mass transfer column to facilitate interaction between fluids when they are flowing within the mass transfer column, said tray comprising: a tray deck having an upper surface; an inlet area on the tray deck for receiving a downward flow of liquid onto the upper surface of the tray deck; a plurality of apertures distributed across an area of the tray deck and extending through the tray deck to permit upward passage of fluid through the tray deck for interaction with the liquid after it leaves the inlet area and flows across and above the area of the tray deck on which the apertures are distributed; an outlet positioned remotely from said inlet area on the tray deck for allowing removal of liquid from the upper surface of the tray deck after it has flowed from the inlet area and interacted with the fluid passing upwardly through the apertures in said area; a plurality of spaced-apart baffle walls extending upwardly from the upper surface of the tray deck and positioned to narrow a width of a flow path of the liquid when it flows from the inlet area to the outlet and to force the liquid to change its direction of flow at least three times and thereby lengthen the flow path; and a downcomer extending downwardly from the outlet to receive liquid when it enters the outlet and then convey it downwardly to a discharge outlet located at a lower end of the downcomer, wherein said downcomer includes an inclined or horizontal portion that causes the discharge outlet to be positioned beneath and in vertical alignment with the inlet area on the tray deck, wherein the inlet area and the outlet are located diagonally opposite from each other at opposite ends of the tray deck. a tray deck having an upper surface; an inlet area on the tray deck for receiving a downward flow of liquid onto the upper surface of the tray deck; a plurality of apertures distributed across an area of the tray deck and extending through the tray deck to permit upward passage of fluid through the tray deck for interaction with the liquid after it leaves the inlet area and flows across and above the area of the tray deck on which the apertures are distributed; an outlet positioned remotely from said inlet area on the tray deck for allowing removal of liquid from the upper surface of the tray deck after it has flowed from the inlet area and interacted with the fluid passing upwardly through the apertures in said area; a plurality of spaced-apart baffle walls extending upwardly from the upper surface of the tray deck and positioned to narrow a width of a flow path of the liquid when it flows from the inlet area to the outlet and to force the liquid to change its direction of flow at least three times and thereby lengthen the flow path; and a downcomer extending downwardly from the outlet to receive liquid when it enters the outlet and then convey it downwardly to a discharge outlet located at a lower end of the downcomer, wherein said downcomer includes an inclined or horizontal portion that causes the discharge outlet to be positioned beneath and in vertical alignment with the inlet area on the tray deck, wherein the inlet area and the outlet are located diagonally opposite from each other at opposite ends of the tray deck.