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Forced and Induced Draft air-cooled heat exchangers

asked Jul 26, 2014 in Process by ChemKB (8,210 points)

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answered Jul 26, 2014 by ChemKB (8,210 points) | selected Oct 30, 2014 by odadmin
 
Best answer

Forced Draft air cooled heat exchangers

Forced draft air cooled heat exchangers diagram

  • Fans are located below the tube bundles
  • Air is pushed across the finned tube surface
  • Better accessibility to the fan for maintenance and fan-blade adjustment
  • Fan and V-belt assembly are not exposed to the hot-air stream that exits from the unit
  • Less structural support is required, and capital cost is lower.
  • Longer mechanical life
  • In theory, the primary advantage of the forced-draft unit is that less power is required. This is true when the air temperature rise exceeds 54°F (30°C), because the fan is pumping denser air.

Induced draft air cooled heat exchangers

Induced draft air cooled heat exchangers diagram

  • Fans are located above the bundle
  • Air is pulled across the finned tube surface
  • Since air velocity approaching the bundle is relatively low, it provides more even distribution of air across the bundle
  • Better suited for exchangers designed for a close approach of product outlet temperature to ambient-air temperature
  • Less likely to recirculate the hot exhaust air, since the exit air velocity is much higher than the forced-draft unit
  • In a service in which sudden temperature change would cause upset and loss of product, the induced-draft unit gives more protection in that only a fraction of the surface (as compared with the forced draft unit) is exposed to rainfall, sleet, or snow.
  • Will transfer more heat by natural convection with fans off because of the stack effect.
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