heat transfer - prado

8/2/2019 Heat Transfer - Prado

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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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