Heat Exchangers Types of heat exchangers Constraints on temperature differences Materials Costing.
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Transcript of Heat Exchangers Types of heat exchangers Constraints on temperature differences Materials Costing.
Heat Exchangers
• Types of heat exchangers
• Constraints on temperature differences
• Materials
• Costing
Shell-and-Tube Heat Exchanger
Double-Pipe Exchanger
Spiral Heat Exchanger
Plate Heat Exchanger
Shell-and-Tube Heat Exchanger
Shell and TubeExchanger TermsFanaritis, J.P., Bevevino, J.W. "Designing shell and tube heat exchangers". Chemical Engineering, 83(13), 62-71, 1976.
Bayonet type - floating inner tubesand floating heads for large temperature differences
Heat Exchanger SelectionBrown, 1985
Shell and Tube Plate Spiral
General purposegas/liquid service
Liquids, low Psteam
Gases, boiling orcondensing
No temperaturecross
High temperaturecross OK
No to moderatetemperature cross
Low fouling Medium fouling High fouling
Good for alloys Limited space
Air-Cooled Exchangers
• Design for worst case - summer air temperatures of 30-35 C
• Typical approach temperature is 50 C• Maximum process fluid temperature ca. 260
C• Typical inlet process fluid temperature <
150 C
Ganapathy, 1978; Ulrich, 1982
Air-Cooled or Fin-Fan Exchanger
Air Cooling vs Water Cooling
Air cooling (+)• corrosive• water pollution• water consumption• maintenance
Water cooling (tower) (+)• temperature control• space• freeze up• noise• achievable T• power
Heat Integration
• Temperature profiles– crossovers– phase changes– correct delta T
• Keeping heat in the process saves utility costs– integrated processes save money– heat exchangers (always) leak
T cross
Design EquationQ U A MTD
Q=amount of heat transferred (from process design)A=heat exchanger areaMTD=mean temperature difference=fTLMf=correction factor for exchanger geometryf=1 for true counter-current; f<1 when cross-flow
TT T
TT
LMh c
h
c
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