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14 TRG-TRC012-EN
notes
period one
Components
Another type of evaporator found in helical-rotary chillers is the direct
expansion (DX) shell-and-tube evaporator. In this type of evaporator the
cool, low-pressure liquid refrigerant flows through the tubes and water fills the
surrounding shell. As heat is transferred from the water to the refrigerant, the
refrigerant boils inside the tubes and the resulting vapor is drawn to the
compressor. Baffles within the shell direct the water in a rising and falling flow
path over the tubes that carry the refrigerant. The resulting turbulence
improves heat transfer.
Since the tubes of a flooded evaporator contain water, they can be mechanically
cleaned without removing the refrigerant charge. The tubes of a direct
expansion evaporator must be chemically cleaned. Additionally, flooded
evaporators are typically more effective, but are more costly.
Direct Expansion Evaporator
refrigerant
refrigerant
vapor
vapor
liquid
liquid
refrigerant
refrigerant
chilled
chilled
water
water
return
return
chilled
chilled
water
water
supply
supply
tube bundle
tube bundle
baffles
baffles
Figure 23