03Heat Exchanger Design.pdf

HEAT EXCHANGER DESIGN
GOALS:
u Role of heat exchangers in chemical processing
u Basic concepts and terminology
u Types of heat exchangers
u Design methodology
ð Sizing
ð Design
ð Rating
8/24/99 Heat Exchanger Design 1
PURPOSE OF A HEAT EXHANGER
u To Heat or Cool a stream flowing from item of
equipment to another. The steam may be a:
ð A liquid
ð A gas
ð A multiphase mixture
u To Vaporize a liquid stream
u To Condense a vapor stream
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SINGLE TUBE PASS, SINGLE SHELL
PASS COUNTERCURRENT HEAT
EXCHANGER
Shell Side Shell Side
Outlet Inlet Nozzle
Nozzle
Tube Side
Tube Side Outlet
Inlet Nozzle Nozzle
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TYPES OF HEAT EXCHANGER SERVICE
u Fluid heated by external utility
ð Steam
ð Hot oil or molten salt
bustion gas (furnace)
ð Electricity (resistive, inductive, microwave)
u Fluid cooled by external utility
ð Cooling water
ð Refrigeration
u Fluid heated or cooled by other process stream
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TYPES OF HEATING AND COOLING
CURVES
Sensible Heat - Heating
Sensible Heat - Cooling
T (K) ponent Condensation or Vaporization
ponent Cooling/Condensation
DUTY Q (kJ/s)
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CALCULATION OF COOLING CURVES
u Sensible Heat: Q = W Cp (Tin - Tout)
(For constant Cp: Q = W (Hin - Hout) otherwise)
u Latent Heat: Q = W λ
u ponent Cooling Curves: Requires point-by-
point flash calculations
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FEASIBLE COOLING CURVE
PAIRINGS
u Corollary of the Second Law of Thermodynamics:
Heat can only be transferred from
a higher temperature to a lower one.
u For heat exchangers this means that the higher
temperature cooling curve and the lower temperature
heating curve cannot intersect.
u When this condition is satisfied, the pairing of a heating
and cooling curve is said to be feasible.
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FEASIBLE COOLING CURVE PAIRINGS
T1in T1in
Countercurr