HEAT EXCHANGER












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DESIGNING THE HEAT EXCHANGER
















HEURISTICS for HEAT EXCHANGERS
  • Take true countercurrent flow in a shell-and-tube exchanger as- a basis.
  • Standard tubes are 3/4 in. OD, 1 in. triangular spacing, 16 foot    long; a shell 1 ft dia accommodates 100 sqft; 2 ft dia, 400 sqft, 3 ft dia, 1100 sqft.
  • Tube side is for corrosive, fouling, scaling, and high pressure fluids.
  • Shell side is for viscous and condensing fluids.
  • Pressure drops are 1.5 psi for boiling and 3-9 psi for other services.
  • Minimum temperature approach is 20°F with normal coolants.
  • Water inlet temperature is 90°F, maximum outlet 120°F.
  • Heat transfer coefficients for estimating purposes, Btu/(hr)(sqft)(°F): water to liquid, 150; condensers, 150; liquid to liquid, 50; liquid to gas, 5; reboiler, 200. Max flux in reboilers, 10,000 Btu/(hr)(sqft).
  •  Double-pipe exchanger is competitive at duties requiring 100-200 sqft.
  • Compact (plate and fin) exchangers have 350 sqft/cuft, and about 4 times the heat transfer per cuft of shell-and-tube units.
  •  Plate and frame exchangers are suited to high sanitation services, and are 25-50% cheaper in stainless construction than shell-and-tube units.
  •  Air coolers: Tubes are 0.75-1.00in. 00, total finned  surface 15-20 sqft/sqft bare surface, U = 80-100 Btu/(hr)(sqft bare surface)(°F), fan power input 2-5 HP/(MBtu/hr), approach 50°F or more.

NOW LET'S PUT THE ABOVE TO WORK

  • SPACE
  • SPACE
  • SPACE
  • SPACE
  • SPACE
















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