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For screw chiller units, the evaporators are mainly divided into two types: full liquid type and dry type. The most fundamental difference between full liquid and dry chiller units lies in the different structures of the evaporators they are equipped with. Full liquid units are paired with full liquid evaporators, while dry units are equipped with dry evaporators.
Structural Principle
Full liquid evaporator: Refrigerant flows in the shell side, while chilled water flows in the tube side. In simple terms, the refrigerant flows outside the copper tube, while the chilled water circulates inside the copper tube.
Dry evaporator: The flow path structure is exactly the opposite. The refrigerant flows through the tube section, while the cold water flows through the shell section. That is, the refrigerant flows inside the copper tube, and the cold water surrounds the outside of the copper tube.
Comparison of Two Types of Evaporators
1. Operating Conditions and Reliability
The wet type unit has numerous components and complex piping circuits, resulting in relatively poor operational stability; it is more suitable for fixed-condition operation and is prone to equipment failures when encountering operational fluctuations. The dry type unit has streamlined components and a simple circuit structure, ensuring reliable and stable operation, and can perfectly adapt to variable-condition operation scenarios.
2. Oil Recovery Performance
Under the condition where lubricating oil and refrigerant are mutually soluble: In the full liquid evaporator, oil recovery is achieved through a suction pump, which is challenging and the oil recovery process is unstable. Moreover, the oil recovery effect directly affects the operating condition of the unit; In the dry-type unit, oil recovery is realized through the pressure difference between high and low pressure in the system, and the oil recovery is smooth and stable.
3. Refrigerant filling volume
The interior of the full liquid evaporator shell is completely filled with refrigerant throughout. The filling volume is large, and it is mostly used in open-type compressors that are prone to refrigerant leakage, as well as some large-capacity screw compressors. The refrigerant filling volume of the dry evaporator is only 1/2 to 1/3 of that of the full liquid type, and the consumables are more economical.
4. Operating Energy Efficiency
The heat exchange efficiency of the full-immersion type unit is higher. Under the same input power, its cooling capacity is 10% to 12% higher than that of the dry-type unit.
5. Equipment Cost
The manufacturing cost of the flooded-type unit is higher, while the dry-type unit is more cost-effective.
Detailed explanation of the advantages and disadvantages of the flooded-type evaporator Advantages
The evaporator has excellent heat exchange efficiency and its overall energy efficiency is higher than that of dry-type evaporators. Under the same cooling capacity, the overall size of the unit is smaller.
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