These are two types.
(i) Long vertical tube falling film evaporator
(ii) Long vertical tube rising film evaporator
(i)Long tube vertical (climbing film) rising film evaporator:
Construction:
This consists of a long tubular heating element incorporating the tubes 25 mm to 50 mm and 3 to 10 meters in length. And also it contains at the top a separator or vapour space for removing entrained liquid from the vapour. The deflector is provided just above the tube sheet.
Working:
The feed at near boiling is fed to the bottom of the evaporator. It is then pumped inside the tubes. Steam is provided on the shell side. Liquid and vapour are separated in the vapour separator at the top. Deflector acts as both primary separator and foam breaker. Multiple effects are used to achieve higher steam economy.
Applications:
Its counter heat exchange design gives the ability to handle foam and forth forming type materials.
(ii)Long tube vertical falling film evaporator:
Construction: This consists of a long tubular heating element incorporating the tubes 50 mm to 250 mm and 3 to 10 meters in length.
Working:
The feed to the evaporator is fed to the top of the evaporator through efficient liquid distributors. Steam is given on the shell side. The concentrate is collected at the bottom. The same operation is repeated in multiple effects to achieve steam economy.
The main problem in this type of evaporator is that of distributing the liquid uniformly as a film inside the tubes. This is done by a set of perforated metal plates above a carefully levelled tube sheet.
Applications:
(i) Long vertical tube falling film evaporator
(ii) Long vertical tube rising film evaporator
(i)Long tube vertical (climbing film) rising film evaporator:
Construction:
This consists of a long tubular heating element incorporating the tubes 25 mm to 50 mm and 3 to 10 meters in length. And also it contains at the top a separator or vapour space for removing entrained liquid from the vapour. The deflector is provided just above the tube sheet.
Working:
The feed at near boiling is fed to the bottom of the evaporator. It is then pumped inside the tubes. Steam is provided on the shell side. Liquid and vapour are separated in the vapour separator at the top. Deflector acts as both primary separator and foam breaker. Multiple effects are used to achieve higher steam economy.
Applications:
Its counter heat exchange design gives the ability to handle foam and forth forming type materials.
(ii)Long tube vertical falling film evaporator:
Construction: This consists of a long tubular heating element incorporating the tubes 50 mm to 250 mm and 3 to 10 meters in length.
Working:
The feed to the evaporator is fed to the top of the evaporator through efficient liquid distributors. Steam is given on the shell side. The concentrate is collected at the bottom. The same operation is repeated in multiple effects to achieve steam economy.
The main problem in this type of evaporator is that of distributing the liquid uniformly as a film inside the tubes. This is done by a set of perforated metal plates above a carefully levelled tube sheet.
Applications:
- Used in desalination industries to separate water and salts in seawater. Optimized models of the multi-effect system having smooth or double fluted tubes are used to obtain better performance ratio. Submerged vertical tube evaporator developed from the classic falling film evaporators are used to provide fresh water with better thermal efficiency.
- It is employed in a high capacity refrigeration system that uses propane as the refrigerant.
- Used widely in liquid food evaporation.