In a falling film evaporator of the vertical-tube type in which liquid to be evaporated is supplied at the top on the outer surface of vertical heat exchanger tubes and the heat medium is supplied to the heat exchanger tubes at the bottom for flow inside the same, at least one larger tube element than the heat exchanger tubes is disposed between and fixed to tube plates at the both ends of the group of tubes to stabilize the group of tubes against tension and especially compression stresses. The larger stabilizing tube element is at its upper end connected with an inlet passage for the primary vapor passing through a steam dome communicating with the upper ends of the tubes and adapted to serve as a transportation channel for directing the primary vapor down through the group of tubes to a chamber formed under the lower tube plate and communicating with the lower, open ends of the heat exchanger tubes which chamber also forms a distributor for supplying the primary vapor to the heat exchanger tubes from underneath and a separator for particles possibly following with the primary vapor which particles are removed together with the primary condensate flowing out of the lower ends of the heat exchanger tubes from the bottom of the said chamber. The group of tubes in the housing is supported by the said upper tube plate and is hanging freely down from it.
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