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ME 414 Thermal-Fluid Systems Design
Project 2: Heat Exchanger Optimization
Instructor: John Toksoy
May 6, 2005
Group Members:
Luke Jones
Justin Gast
Mike Hughett
Department of Mechanical Engineering, IUPUI
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Problem Statement Design a heat exchanger given 80,000kg/hr of distilled water will
enter at 35C and leave at 25C and transfer heat to
140,000kg/hr raw water entering from a 20C supply. Desired heat transfer rate = = 928.5 kW
No baffles, neglect fouling, single pass.
Optimize the weight, shell and tube pressure drops, and heat
transfer of the design using the DOE capabilities of both Matlab
and Minitab software.
TCm p&
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Tools Utilized Matlab
Utilized the provided Matlab code to perform the heat exchanger
analysis Minitab
Used in the selection of critical design parameters
Provided tools needed to optimize Matlab heat exchanger design
calculations
Aided in optimization
Iterative optimization process
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Where to Start? Input given values from problem definition
Obtained desired to calculated heat transfer ratio of 1 by trial and
error Ran DOE study using Minitab to find the main effects of the
variables and their interactions
Eliminated insignificant variables
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Funnel EffectShell ID, Tube OD, Length, Tube Material, Shell
Thickness, Fluid Allocation, Layout Angle,Shell Thickness
2-3 Critical
Variables
Minitab
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Main Effects Plots
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Design Decisions
Counter Flow
Parallel Flow Not an Option
1.25 Pitch Ratio (rule of thumb)
Square Pitch
Clean surfaces 90 degree layout angle
Tube Material
Aluminum: Heat Transfer Low Weight
Shell Thickness set to 1 mm (determined from
hoop stress analysis)
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Elimination from Evaluation
After more Main effects plots were run, the 3 key variables
discovered were: length, tube OD, and shell ID
Next, a multi-level DOE was run in Matlab to determine good
starting points for design optimization
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Main Effects of 3 Critical Parameters
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Heat Exchanger Optimization
Analyzed Factorial Design to create Pareto charts of design parameters.
This shows the weight each variable has on the design specification
Verified that the statistical p-values were below 0.1
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Iterative Optimization
DOE 1 DOE 2 DOE 3
DOE 4 DOE 5
+/- 20% +/- 15%
+/- 5%
+/- 10%
(Matlab
Check)
(Matlab
Check)
(Matlab
Check)
(Matlab
Check)
Matlab Results:
Weight = 1051 kg
P Tube = 978 Pa
P Shell = 914 Pa
Q = 928.6 kW
(Matlab
Check)
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Cost Consideration
While custom parts provide the most efficient heat exchanger design,
manufacturing costs must be considered in the Total Cost of Ownership
Using standard tube sizes greatly reduces initial costs, thereby reducing the TCO
TCO = Initial Costs + Maintenance + Repairs
Standard Tube and Shell Size Optimization:
Weight = 1005 kg
Heat transfer rate = 928.3 kW
Desired-to-calculated ratio of 1.00
Shell side pressure drop = 788 Pa
Tube side pressure drop = 687 Pa
Even Better than the Minitab Optimization!!
Selected Material Sizes:
Shell Diameter: 21.25 inches
Tube Diameter: 20BWG inch
Tube Length: 3.477 meters*
* There is no defined standard length
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Conclusions
Heat Exchanger optimization was a success
The standard tube and shell diameters provides the optimal weight,
tube and shell pressure drops, and desired heat transfer One concern: the average tube velocity is 0.28 m/s for our optimal
design, which is lower than the recommended velocity to prevent
settling
Because distilled water is being used in the tubes, settling is
unlikely
TCO of our design is minimized:
Low material weight
initial costs minimized
Low pressure drops initial costs and operational costs
minimized
Square pitch maintenance costs minimized (time=money!!)
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Questions?
