Heat Exchangers - Fouling and Reduced Heat Transfer
Heat-transfer in heat exchangers are reduced by fouling.
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During operation with liquids and gases a dirt film may build up on the heat exchanger surfaces . The deposit film is referred to as fouling.
Increased thermal resistance caused by the deposit can normally only be obtained from tests or experience. The fouling factor can be determined as
Rd = 1 / Ud - 1 / U (1)
where
Rd = fouling factor - or unit thermal resistance of deposit (m2K/W)
Ud = overall heat transfer coefficient of heat exchanger after fouling (W/m2K)
U = overall heat transfer coefficient of clean heat exchanger (W/m2K)
(1) can also be expressed as:
Ud = 1 / (Rd + 1 / U)
Typical Fouling Factors
- Alcohol vapors : Rd = 0.00009 (m2K/W)
- Boiler feed water, treated above 325 K : Rd = 0.0002 (m2K/W)
- Fuel oil : Rd = 0.0009 (m2K/W)
- Industrial air : Rd = 0.0004 (m2K/W)
- Quenching oil : Rd = 0.0007 (m2K/W)
- Refrigerating liquid : Rd = 0.0002 (m2K/W)
- Seawater below 325 K : Rd = 0.00009 (m2K/W)
- Seawater above 325 K : Rd = 0.0002 (m2K/W)
- Steam : Rd = 0.00009 (m2K/W)
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