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)
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)
Work, heat and energy systems.
Conductive heat transfer takes place in a solid if there is a temperature gradient.
Heat transfer between a solid and a moving fluid is called convection. This is a short tutorial about convective heat transfer.
Make-up water to steam boilers should be treated with oxygen scavengers to avoid serious corrosion problems.
Overall heat transfer coefficients in common heat exchanger designs - tubular, plate or spiral.
Average overall heat transmission coefficients for fluid and surface combinations like Water to Air, Water to Water, Air to Air, Steam to Water and more.
Walls or heat exchangers - calculate overall heat transfer coefficients.
Heat transfer due to emission of electromagnetic waves is known as thermal radiation.