Heat Exchanger Design Thermal / Fluid System Design Final Project Department of Mechanical Engineering Fall 2005 December 13, 2005 Team Members: Andrew Burian Jack Copenhaver Chris Haire Brandin Ray Professor: John Toksoy

Required Design Parameters Heat Exchanger Must Cool the Chemical From 35°C to 25°C 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 20°C Heat Exchanger Must Cool the Chemical From 35°C to 25°C 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 20°C

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

Initial Possible Factors Effecting Heat Exchanger Design Mass Flow Rate (Shell Side) Tube Length Shell I.D. Tube Pitch Tube Material Shell Thickness 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

“One Factor at a Time” Study

Factors Found to Have Greatest Effect on Weight and Heat Transfer Tube Length Shell I.D. Baffles Tube O.D. Tube Length Shell I.D. Baffles Tube O.D. Number of Tubes Pitch (Square or Triangular) Mass Flow Rate

Main Effects Plots With Seven Factors

Final Factors Tube Length Tube Material Tube O.D. Shell I.D. Tube Length Tube Material Tube O.D. Shell I.D.

Main Effects Plots With Final Factors

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

Initial vs. Final Specifications InitialFinal Mass Flow Rate ……… kg/s43.0 kg/s Flow Direction ………….Counter FlowCounter Flow Shell I.D. ……………… m m Shell Thickness ………..2.0 mm2.0 mm Shell Material …………..BronzeStainless Steel Tube O.D. ………………9.525 mm mm Tube Thickness ……… mm0.559 mm Tube Length ……………3.2 m4 m Number of Tubes……… Tube Material…………...AluminumStainless Steel Tube Pitch……………….Triangle (30°)Triangle (60°) Baffle space…………… m2 m Baffle Cut……………… m0.150 m InitialFinal Mass Flow Rate ……… kg/s43.0 kg/s Flow Direction ………….Counter FlowCounter Flow Shell I.D. ……………… m m Shell Thickness ………..2.0 mm2.0 mm Shell Material …………..BronzeStainless Steel Tube O.D. ………………9.525 mm mm Tube Thickness ……… mm0.559 mm Tube Length ……………3.2 m4 m Number of Tubes……… Tube Material…………...AluminumStainless Steel Tube Pitch……………….Triangle (30°)Triangle (60°) Baffle space…………… m2 m Baffle Cut……………… m0.150 m

The Argument for Stainless Steel

Stainless Steel Pros Cons Not Chemically Reactive Easy to Clean Not as Easily Damaged During Cleaning Food Industry Uses Easy to Repair 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

Aluminum Pros Cons Easy to Work With Light Weight Slightly Increased Heat Transfer 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)

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

H. E. Specifications and Properties Shell I.D. = m Shell Thick. = 2 mm Tube O.D. = 9.25 mm Tube Thick. = mm Shell I.D. = m Shell Thick. = 2 mm Tube O.D. = 9.25 mm Tube Thick. = mm ∆ P Shell = 3000 Pa ∆P Tube = Pa E = 190 GPa α = 17.2 e – 6 σ Y = 6.55 GPa

Calculated Stresses σ Y = 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 Shell Hoop Stress = 2.29 GPa Shell Long. Stress = 1.14 GPa Tube Hoop Stress = 1.02 GPa Tube Thermal Stress = 19.7 KPa

Questions?

Appendix

MATLAB Results With Optimized Factors Desired Heat Transfer Rate = W Calculated Heat Transfer Rate = W Difference = W Desired-to-Calculated Ratio = 1.00 HE Pressure Drop ===================== Shell Side Delta-P = Pa Tube Side Delta-P = Pa Heat Exchanger Weight ===================== Shell Weight = kg Tube Weight = kg Shell Fluid Weight = kg Tube Fluid Weight = kg Total HE Weight = kg Desired Heat Transfer Rate = W Calculated Heat Transfer Rate = W Difference = W Desired-to-Calculated Ratio = 1.00 HE Pressure Drop ===================== Shell Side Delta-P = Pa Tube Side Delta-P = Pa Heat Exchanger Weight ===================== Shell Weight = kg Tube Weight = kg Shell Fluid Weight = kg Tube Fluid Weight = kg Total HE Weight = kg Tube Side Heat Transfer Parameters ===================================== === Number of Tubes N = Number of Passes = 1.00 Tubes OD OD = m Tubes ID ID = m Tube Length L = m Tube Flow Area Af = m2 Tube Solid Area As = m2 Tube Pitch PT = m Average Velocity V = 0.73 m/s Mass Velocity G = kg/m2.s Reynolds Number Re = TURBULENT Nusselt Number Nu = HT Coefficient h = W/m2.C

Overall Heat Transfer Coefficient ============================= ========= U (Tube Outside Area) = W/m2.C Heat Transfer Rate ============================= ========= Desired Heat Transfer Rate = W Calculated Heat Transfer Rate = W Difference = W Desired-to-Calculated Ratio = 1.00 Shell Side Heat Transfer Parameters ============================= ========= Shell ID = m Shell Cross Sec Area = m2 Shell Flow Area = m2 Baffle Space = m Number of Baffles = m Shell Equivalent Dia = m Mass Velocity G = kg/m2.s Reynolds Number Re = TURBULENT Nusselt Number Nu = HT Coefficient h = W/m2.C

Additional Plots From Seven Factors MINITAB Run

Pareto Charts With All Combinations Considered

Pareto Charts With Irrelevant Combinations Removed

Credits Minitab 14 MatLab 7.0 Minitab 14 MatLab 7.0