Abstract: Apparatus for desubliming, condensing or evaporating a fluid. The apparatus includes a chamber and at least one tubular member for desubliming, condensing or evaporating the fluid on the outer surface of the at least one tubular member. The chamber is provided with at least one inlet for the fluid and at least one outlet for the condensate and/or evaporate, and at least one supply and at least one discharge for a cooling and/or heating fluid. The tubular member includes an outer member and an inner member enclosed within the outer member. The inner member is in communication with the supply at a first end. The outer member is in communication with the discharge at a first end. The outer member is closed at a second end. The inner member is open and mouths into the outer member at a second end.