A rising film or vertical long tube evaporator is a type of evaporator that is essentially a vertical shell and tube heat exchanger. The liquid being evaporated is fed from the bottom into long tubes and heated with steam condensing on the outside of the tube from the shell side. This is to produce steam and vapor within the tube bringing the liquid inside to a boil. The vapor produced then presses the liquid against the walls of the tubes and causes the ascending force of this liquid. As more vapor is formed, the center of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards. This phenomenon of the rising film gives the evaporator its name.
Applications: There is a wide range of applications for rising tube evaporators, including effluent treatment, production of polymers, food production, thermal desalination, pharmaceuticals, and solvent recovery.