heat transfer - prado
TRANSCRIPT
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Evaluation of the Overall
Heat Transfer Coefficient for aPilot Scale Heat Exchanger
Josie Prado
Erin Hadi
Trevor Binney
February 3rd, 2005
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Project Objectives
Project Planning and Execution
Background and Experimental Procedure Results and Discussion
Conclusions
Recommendations for Future Work
Presentation Overview
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Project Objectives1) Experimentally determine the overall heat transfer
coefficient (Uo)
Laminar and turbulent flow regimes
Co-current and counter current operation2) Correlate Uo to the liquid flow rate in the inner pipe inthe form Uo = aV
b
3) Compare experimental results with predicted and
reported values4) Investigate the effect of the steam trap
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Project Planning
1) Design of Experiment
Review equipment operation
Determine what parameter(s) will be varied
Determine what measurements to take2) Rotameter Calibration
Cold water rotameter
Range ~ 5 -100
Quench water rotameter Range ~ 1.5-10
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Project Planning
3) Data Collection
Co-current flow
Without steam trap
With steam trap Counter-current flow
Without steam trap
With steam trap
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Project Planning
4) Data Analysis
Empirical Analysis
Determination of Uo from experimental data
Correlation of Uo to cold water flow rate by fitting thedata to a power curve
Theoretical Analysis
Performed from fundamental principles of heattransfer
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Project Planning
Roles and Responsibilities
Josie Prado (Team Leader)
Temperature, pressure, and flow rate measurements
Trevor Binney (Safety Coordinator)
Scale operator and timer
Erin Hadi (Operations Manager)
Data Entry
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Project Planning
Safety Issues
Steam burns
Mitt was used for all steam valve adjustments
Steam trap configuration was checked before makingadjustments
Tripping Hazards
Hoses were kept away from major traffic areas
Slipping Hazards
Rubber sole shoes were worn at all times
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Equipment Dimensions &Specifications
Double pipe exchanger Inner Pipe: 1ID/1.125OD
Outer Pipe: 2ID/2.125OD
Length: 60 Cold water supply
Tap water 9 to 10 C
Steam Supply 26 to 29 psig
~128 C
ri
ro
Steam
Water
Inner pipe(Cu)
Outer pipe(Cu)
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Background
Resistance to Heat Transfer
Convective: between surface and adjacent
fluid Water/pipe interface
Steam/pipe interface
Conductive:
Through the inner pipe
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Heat Exchanger SetupCounter-Current Operation
Water in
Steam in
Water Out
Steam Out
Thermocouples
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Experimental Procedure Rotameter Calibration
Set rotameter flow rate to a specific value
Measure mass of water entering the drumover time
10 lbs of water per interval of time Calculate flow rate in lb/s
Generate calibration curve
Physical Constraint
Flow rate required for laminar flow isoutside the rotameters measuring range
Max laminar flow rate = 0.08 lb/s
Quench rotameter reading of 1.35
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Experimental Procedure
Collecting Data Set equipment configuration
Co-current/Counter-current
Steam trap ON/OFF
Set flow rate & wait for steady state to be reached
Record stream temperatures, pressure, and flow rates
Take several readings at each set of conditions
Weigh and time the collection of steam and quench water
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Experimental Data Analysis
Empirical Uo was calculated from data
For co-current:
For counter-current:
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Results
Quencher Calibration Data
y = 0.0528x + 0.0087
R2 = 0.9985
0.0
0.1
0.1
0.2
0.2
0.3
0.3
0.4
0.4
0.5
0 2 4 6 8
Rotameter Reading
Massflowrate(lb/s)
Quencher Linear (Quencher)
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Results Cold Water Calibration Data
y = 0.0129x + 0.0256
R2 = 0.9983
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60
Rotameter reading
Massflowrate(lb/s)
Cold Water Linear (Cold Water)
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Results
Configuration # Data pts. Correlation R2
Co-current w/o steam trap 18 Uo = 2931.9*V0.1857 0.95
Counter-current w/o steam trap 22 Uo = 2540.8*V0.2154 0.89
Co-current w/ steam trap 9 Uo = 2950.9*V0.1846 0.99
Counter-current w/ steam trap 9 Uo = 2582.8*V0.3114 0.99
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Results
Overall Heat Transfer Coefficient vs. Water
Velocity
2000
2100
2200
2300
2400
2500
26002700
2800
2900
3000
0.00 0.20 0.40 0.60 0.80 1.00 1.20
water velocity (m/s)
Uo(W/m2K
)
Co-current without steam trapCounter-current without steam trapPower (Co-current without steam trap)Power (Counter-current without steam trap)
Published data: Exchanger Uo values between 2280 3400 W/m2K
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Results Co-current & Counter-current Uo vs. water flow rate with and
without steam trap in operation:
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
water velocity (m/s)
Uo(W/m2K
)
counter-current steam trap off counter-current steam trap on
co-current steam trap on co-current steam trap off
Power (counter-current steam trap on) Power (counter-current steam trap off)
Power (co-current steam trap off) Power (co-current steam trap on)
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Results & Discussion
Why is Uo higher for co-current flow than for countercurrent flow?
Why is the change in enthalpy of steam much lower than
the change in enthalpy of water? Hwater ~ 42 kJ/lb
Hsteam ~ -11 kJ/lb
Is it possible that some of the steam is condensing?
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Results and Discussion
Effect of condensation on co-current vs.counter current operation:
More drastic temperature difference in
co-current mode leads to immediateformation of a condensate film
In counter-current flow, condensate filmformation is likely to begin further down the
pipe
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Results & Discussion
Comparison with theoretical values
Assuming no steam condenses:
Uo = 185 - 205 W/m2K
Taking condensation into account
Uo = 900 - 1740 W/m2K
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Conclusions
1) Empirical Uo values are verified by publishedvalues
2) Theoretical analysis does not invalidate
experimental values if steam condensation istaken into account
3) The steam trap did not have a significant effect onthe heat exchanger performance
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Recommendations for Future Work
1) Investigate the effect of water velocity on Uo inlaminar region
A more sensitive rotameter would be required
2) Investigate heat exchanger performance whilevarying both water and steam flow rate
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References
Incropera, Frank P. and David P. Dewitt. (2002) Fundamentals ofHeat and Mass Transfer. John Wiley and Sons. New York, pp. 470,486, 492, 647, 723.
Perrys Chemical Engineers Handbook, 7th Edition (1997). R.H.Perry, D.W. Green, and J.O. Maloney, Eds. McGraw Hill: New York,pp. 5-20, 10-5, 11-4
Welty, James R, Charles E. Wicks, Robert E. Wilson, and Gregory
Rorrer (2001). Fundamentals of Momentum, Heat, and MassTransfer. Fourth Edition. John Wiley and Sons: New York, pp.201-209, 374, 723, 727, 733.
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Questions?