Rising Film Evaporator

The feed is given at bottom of shell & tube type heat exchanger and rises in tubes. Heat is given on the shell side by heating medium. As feed receives heat, vapor generated pushes the liquid on the wall as a film and lifts the liquid upwards. As more vapor is formed, the centre of the tube will have a higher velocity which forces the remaining liquid against the tube wall forming a thin film which moves upwards. The mixture of liquid & vapor are separated at top in vapor- liquid separator.