A flow device intended for a two-phase flow processing enclosure of the natural counter-flow type, in which an ascending gaseous flow and a descending liquid flow circulate. The device is formed by an appreciably horizontal tray having openings for the passage of the ascending gaseous flow, and a channel for recovering the descending liquid flow, the channel discharging into a flow orifice. The flow device includes a single guide device extending beneath the tray and connected to the flow orifice in such a way that the liquid flows on its outer wall. Also, a processing enclosure, particularly for processing a hydrocarbonated or aqueous type liquid flow, containing the flow device.