Evaporator and condenser are sometime named as heat exchanger. As the name said, it is for hear exchanging. Evaporator is for absorption the heat from the air for air conditioners, or from water for chillers. How this realize? The refrigerant goes into the evaporator in low-pressure and low temperature status. The evaporation of refrigerant happens here, and the heat absorbed while evaporating. In this case, the heat in the room is transited to the refrigerant and the refrigerant goes to next step, so the heat indoor is taken away.
The Type of Evaporator
There are different types of evaporators. They have a common purpose, to help the refrigerant keep close contact with the air or water, and to enlarge the contact surface as much as possible. Following are some most commonly used evaporators.
1. The Copper Tube with Aluminum Fins Evaporator
This is commonly used in mini-split air conditioners, PTAC’s, VRF/VRV system, rooftop packaged air conditioners, etc. It is produced by multiple copper tubes go through countless layers of Aluminum fins. The copper tubes are closely contact with the Aluminum fins. Like this picture. Moreover, the Copper tubes are always inner grooved. The contact surface is enlarged a lot. There is normally a fan behind the evaporator, the fan will suck the air into the unit, and the air goes through evaporator in this process. The air contact with the fins, and the heat in the air will transit to the refrigerant inside the evaporator. It can freely adjust the size and shape, so it is widely used in above mention air conditioning units.
Another function of copper tube with aluminum fins evaporator is dehumidifying. As the evaporator is cold, the moisture in the air will be condensed on the fins. There is normally a drain pan under the evaporator to collect the condensed water and lead it float away. The air is kept dry in this way.
2. Dry Type Evaporator
There is a name called Shell and tube evaporator. Dry type is one of it.
This is mostly used in large HVAC units, like chillers. This evaporator is produced as multiple tube package inside a shell. The refrigerant goes inside the tubes, and the water is between the tube and shell. The refrigerant can contact with water in this way. There are ways in and out for water on the shell. The water floats through the evaporator, so the heat in water will be transit to the refrigerant. Dry type evaporator is the most commonly used shell and tube evaporator.
Its advantages are:
It makes unit easily control;
Not much refrigerant need to be charges in the cooling system;
But the disadvantage is heat exchange efficiency is not very high.
3. Flooded Type Evaporator
It is another type shell and tube evaporator. It is similar to the dry type evaporator, but the ways for refrigerant and water are reversed. The water float in the tubes now while the refrigerant is between the tube and shell.
The main advantage is high heat exchange efficiency. It is about 2 times higher than Shell and tube type evaporator. But the main disadvantage is more refrigerant need to be charged than dry type, so the cost will be higher accordingly.
There are other types evaporators like Falling film evaporator, Micro-channel aluminum evaporator, etc. We don’t discuss them here as they are not much used in HVAC units.
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