Evaporators are heat transfer surfaces in which there is a volatile liquid refrigerant gets vaporizes by removing the heat from the refrigerated space or product. The liquid refrigerant enters the evaporator from the expansion valve where it gets boiled off and absorbs the latent heat from the space.
To evaporate the refrigerant at a lower temperature, it is necessary to keep it os low pressure in the evaporator. The liquid refrigerant boils and changes to a vapor state in the evaporator, it is due to the low pressure. Evaporators absorb large quantities of heat and then cool down.
There are a variety of evaporators. Every evaporator distinguishes in the way to achieve heat transfer. Let’s learn about some of them.
Kinds of Evaporators:-
This evaporator consists of tubular heat exchangers for concentrating a feed. Forced circulation evaporators are used where there is a high chance of feed or product liquor slating or scaling, it is also used when the feed has a high viscosity and the thermal and flow properties of the process liquor are poor.
In this mechanism, the feed is pumped at high velocity through the tubes. It is done to ensure the heat transfer coefficient. This evaporator is best for the crystallization of slurries and other solutions.
The working of such an evaporator achieves high velocity and low residence time in a small space. This is due to the high heat transfer. It also prevents the feed from reacting with the vessel of evaporation.
This is a shell and tube-type heat exchanger. The liquid that needs to be evaporated is fed into the evaporator from the bottom. The liquid within the evaporator boils up into vapor as there is a condensation of steam on the outer surface of the vertical tubes. When the liquid progresses up the tube, the volume of vapor increases and leads to higher central core velocity.
Because of this high velocity, the remaining liquid of the tube creates a thin film that moves rapidly. This rapid movement also leads to a high heat transfer coefficient and a reduction in the residence time.
Falling FilmThis evaporator is used to evaporate heat-sensitive liquids. In this, the feed enters from the top of the evaporator and gets distributed through the heating tubes. The liquid flows and forms a thin film on the tune walls and evaporates partially. The heating medium provides heat that ensures a high heat-transfer coefficient. After this, the liquid and the vapor flow downwards. The design of the distributor head of the falling film is in such a way that ensures the uniform wetting of the tube surfaces.
Agitated Thin Film
This evaporation consists of jacketed shells and high-speed rotors. The working of this evaporator includes the feed that enters the evaporator from the top. With the help of a fast-spinning rotor, the feed is agitated and spread out into a thin film on the shell walls. Then it distributes the liquid in the form of a thin film on the heated wall. After that, the rotor wipes the fluid from the walls which are inside the heating shells.
The working principle of this evaporator enables businesses to achieve extremely high evaporation rates.
This is the evaporator where the process needs multiple evaporators. In this when the water vapor discharges from one effect, the next effect uses it as the heating medium which consists of a lower boiling point.
Many operations use this multi-effect evaporator to concentrate aqueous fluids and also allow obtaining the product at the lowest temperature.
In this evaporator, the first effect gets heated up with the raw steam. The other effect gets the arrangement of subsequently reducing boiling points. Its principles enable the operation to reuse the latent heat in the water vapor. In such evaporators, the feed moves from high to low pressure which eliminates the need to pump the feed.
Wrapping it up:-
The evaporator is the mechanism that converts the fluid from liquid to vapor or gaseous form. In this above article, we discussed the types of evaporators as well.
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