This is the evaporator that conducts evaporation under reduced pressure which areused to evaporate the materials substances like thermolalible substances.
In these type of evaporators some mechanical device are fitted to circulate the contents heating in it. For example an evaporating pan in which the materials is agitated by a stirring rod or by a mechanical propeller.
The liquid is circulated by means of a pump and as it is under pressure in the tubes the boiling point is raised and no boling take places. And it enters the body of the evaporator.
In forced circulation evaporator liquid is circulated through the tubes at high pressure by means of a pump. Hence boiling does not takes places because boiling point is elevated. Forced circulation of the liquids also creates some form of agitation. When the liquid leaves the tubes and enters the vapor head, pressure falls suddenly. This lead to the flashing of super heated liquor. Thus the evaporation is effected.
The construction of forced circulation evaporator consists of steam jacketed tubes are held between two tube sheet. The tube measures 0.1 m inside diameter and 2.5 m long.
The parts of the tubes projects in to the vapor head which consists of a deflector. The vapor head is connected to a return pipe which runs down wards and enters in to the inlet of a pump.
Steam is introduced in to the calendria. Pump sends the liquid to the tube with a positive velocity. As the liquid move up through the tube it gets heated and begins to boil.
As result the vapour and liquid mixture rushes out of the tubes at a high velocity. This mixture strikes the deflector in n effective separation of liquid and vapour.
The vapour enters the cyclone separator and leaves the equipment. The concentrated liquid enters to the pump for furthur evaporation. Finlly the concentrated product is collected.
1. If evaporation is conducted under reduced pressure, forced circulation evaporator is suitable for thermolabile substances.
2. This method is used for the concentratin of insulin and liver extracts.
3. It is well suited for crystallizing operation where crystals are to be suspended at all times.
1. In forced circulation evaporator there is a rapid liquid movement due to high heat transfer coefficient.
2. Salting, scaling and fouling are not possible due to forced circulation.
3. This evaporators is suitable for themolabile substances because of rapid evaporation.
4. It is suitable for the viscous preparation because pumping mechanism is used.
1. In forced circulation evaporator the hold up of liquids is high. The equipments is expensive because the power is required for the circulating the liquids.
1. Mehta RM, Pharmaceutics-I: heat processes - evaporation (1996), Page no: 166 - 169.
2. C.v.s subrahmanyam et al., pharmaceutical engineering principles and practices - evaporation, 2001, page no. 351 - 352.