The invention relates to a compact rectifying unit for separation of mixed fluids using for heat transfer purpose a fluid heat carrier and its vapours on one of the sides of heat and mass exchanging walls. In order to increase the efficiency of the heat and mass exchange process, the heat and mass exchange tubes of the rectifying part and/or of the evaporator part have means to provide irregular/varying amounts of heat transfer between the inside and the outside of tube wall along the height of the heat and mass exchange tubes. This allows for a reduction in the rectification column height by 3-10 times.