Heat Exchanger Design Thermal Fluid System Design Final Project Department of Mechanical Engineering

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Heat Exchanger DesignThermal / Fluid System
DesignFinal ProjectDepartment of Mechanical
EngineeringFall 2005December 13, 2005Team
MembersAndrew BurianJack CopenhaverChris
HaireBrandin RayProfessor John Toksoy
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Required Design Parameters

• Heat Exchanger Must Cool the Chemical From 35C
  to 25C
• Cannot Exceed 7m In Length or 2m in Diameter
• Minimize Heat Exchanger Shell Diameter and Tube
  Length to Reduce Cost
• Minimize Pressure Drop
• Chemical Mass Flow Rate Fixed at 80 kg/hr
• City Water to be Used as Cooling Fluid With an
  Inlet Temperature of 20C

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Assumptions

• Isothermal Material Properties (Shell and Tube)
• Constant Properties
• Steady State
• Incompressible Fluids
• 24 Hour Duty Cycle
• Heat Transfer Through Shell is Minimal

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Initial Possible Factors Effecting Heat
Exchanger Design

• Mass Flow Rate (Shell Side)
• Tube Length
• Shell I.D.
• Tube Pitch
• Tube Material
• Shell Thickness

• Tube O.D.
• Tube Thickness
• Number of Tubes
• Baffle Spacing
• Baffle Cut
• Shell Material
• Flow Direction

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One Factor at a Time Study
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Factors Found to Have Greatest Effect on Weight
and Heat Transfer

• Tube Length
• Shell I.D.
• Baffles
• Tube O.D.

• Number of Tubes
• Pitch (Square or Triangular)
• Mass Flow Rate

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Main Effects Plots With Seven Factors
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Final Factors

• Tube Length
• Tube Material
• Tube O.D.
• Shell I.D.

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Main Effects Plots With Final Factors
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Final Design Specifications(Clean Heat Exchanger)

• Shell I.D. .3048m
• Shell Thick. 2mm
• Tube O.D. 9.25mm
• Tube Thick. .559mm
• Number of Tubes 550
• Weight 590.80kg

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Initial vs. Final Specifications

• Initial Final
• Mass Flow Rate .. 59.0 kg/s 43.0 kg/s
• Flow Direction . Counter Flow Counter Flow
• Shell I.D. .. 0.3784 m 0.3048 m
• Shell Thickness .. 2.0 mm 2.0 mm
• Shell Material .. Bronze Stainless Steel
• Tube O.D. 9.525 mm 9.525 mm
• Tube Thickness .. 0.889 mm 0.559 mm
• Tube Length 3.2 m 4 m
• Number of Tubes 889 550
• Tube Material... Aluminum Stainless Steel
• Tube Pitch. Triangle (30) Triangle (60)
• Baffle space.. 0.75 m 2 m
• Baffle Cut.. 0.116 m 0.150 m

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The Argument for Stainless Steel
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Stainless SteelPros Cons

• Not Chemically Reactive
• Easy to Clean
• Not as Easily Damaged During Cleaning
• Food Industry Uses
• Easy to Repair

• Harder to Machine
• Shipping Costs/Requirements
• Small Decrease in Heat Transfer

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AluminumPros Cons

• Easy to Work With
• Light Weight
• Slightly Increased Heat Transfer

• Soft Easier to Damage During Maintenance
• Hard to Repair
• Anodic to Most Other Metals
• Chemically Reactive
• Weak (With Respect to Stainless)

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Stress Analysis

• Using General Material Properties for Annealed
  300 Series Stainless Steel and Worse Case Heat
  Exchanger Pressures Taken From D.O.E. Study

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H. E. Specifications and Properties

• Shell I.D. 0.3048 m
• Shell Thick. 2 mm
• Tube O.D. 9.25 mm
• Tube Thick. 0.559 mm

• ? PShell 3000 Pa
• ?PTube 14000 Pa
• E 190 GPa
• a 17.2 e 6
• sY 6.55 GPa

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Calculated Stresses sY 6.55 GPa

• Shell Hoop Stress 2.29 GPa
• Shell Long. Stress 1.14 GPa
• Tube Hoop Stress 1.02 GPa
• Tube Thermal Stress 19.7 KPa

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Questions?
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Appendix
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MATLAB Results With Optimized Factors

• Desired Heat Transfer Rate 928500.92 W
• Calculated Heat Transfer Rate 929320.42 W
• Difference -819.50 W
• Desired-to-Calculated Ratio 1.00
• HE Pressure Drop
• Shell Side Delta-P 2181.04 Pa
• Tube Side Delta-P 5363.92 Pa
• Heat Exchanger Weight
• Shell Weight 60.72 kg
• Tube Weight 273.66 kg
• Shell Fluid Weight 134.82 kg
• Tube Fluid Weight 121.61 kg
• -----------
• Total HE Weight 590.80 kg

• Tube Side Heat Transfer Parameters
• Number of Tubes N 550.00
• Number of Passes 1.00
• Tubes OD OD 0.0095 m
• Tubes ID ID 0.0084 m
• Tube Length L 4.0000 m
• Tube Flow Area Af 0.0305 m2
• Tube Solid Area As 0.0392 m2
• Tube Pitch PT 0.0119 m
• Average Velocity V 0.73 m/s
• Mass Velocity G 727.87 kg/m2.s
• Reynolds Number Re 7657.84 TURBULENT
• Nusselt Number Nu 63.05
• HT Coefficient h 4629.32 W/m2.C

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• Overall Heat Transfer Coefficient
• U (Tube Outside Area) 1975.17 W/m2.C
• Heat Transfer Rate
• Desired Heat Transfer Rate 928500.92 W
• Calculated Heat Transfer Rate 929320.42 W
• Difference -819.50 W
• Desired-to-Calculated Ratio 1.00

• Shell Side Heat Transfer Parameters
• Shell ID 0.3048 m
• Shell Cross Sec Area 0.0730 m2
• Shell Flow Area 0.1219 m2
• Baffle Space 2.0000 m
• Number of Baffles 1.0000 m
• Shell Equivalent Dia 0.0069 m
• Mass Velocity G 352.69 kg/m2.s
• Reynolds Number Re 2576.25 TURBULENT
• Nusselt Number Nu 51.07
• HT Coefficient h 4502.58 W/m2.C

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Additional Plots From Seven Factors MINITAB Run
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Pareto Charts With All Combinations Considered
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Pareto Charts With Irrelevant Combinations Removed
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Credits

• Minitab 14
• MatLab 7.0