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Page 1: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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ยฉ Faith A. Morrison, Michigan Tech U.

CM3110 Transport IPart II: Heat Transfer

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Heat Transfer with Phase Change Evaporators and Condensers

Professor Faith Morrison

Department of Chemical EngineeringMichigan Technological University

ยฉ Faith A. Morrison, Michigan Tech U.

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See also Incropera et al., Fundamentals of Heat and Mass Transfer, 6th edition, 2007, Chapter 10, Boiling and Condensation

Heat Transfer with Phase Change

Heat Transfer with Phase Change

1. forced convectionโ€ข laminarโ€ข turbulent

2. natural convectionNewtonโ€™s law of cooling

๐‘ž๐ด

โ„Ž ๐‘‡ ๐‘‡

So far we have discussed heat transfer at a boundary due to convection in the fluid.

Page 2: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Heat Transfer with Phase Change

1. forced convectionโ€ข laminarโ€ข turbulent

2. natural convection3. phase change

When a phase change takes place, the temperature on one side is CONSTANT, but the presence of boiling/condensing fluids produces heat transfer.

โ€ข Important in evaporation, distillationโ€ข LARGE hโ€ขItโ€™s important to know in which regime you operateโ€ขEach regime has different correlations

ยฉ Faith A. Morrison, Michigan Tech U.

3

Newtonโ€™s law of cooling

๐‘ž๐ด

โ„Ž ๐‘‡ ๐‘‡

So far we have discussed heat transfer at a boundary due to convection in the fluid.

Heat Transfer with Phase Change

vapor phase

liquid phase

satTBoiling

resistance to heat transfer

At low ฮ”๐‘‡, few bubbles form, and heat transfer is by natural convection.

As ฮ”๐‘‡ increases, more bubbles form, increasing convection (flow) in the liquid phase, increasing h.

heat

ยฉ Faith A. Morrison, Michigan Tech U.

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๐‘‡ ๐‘‡

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

Page 3: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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vapor phase

liquid phase

satT Film Boiling

resistance to heat transfer

As ฮ”๐‘‡ increases further, a film appears and grows, increasing resistance to heat transfer

heat

ยฉ Faith A. Morrison, Michigan Tech U.

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๐‘‡ ๐‘‡

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

Geankoplis 4th ed, p284

natu

ral

conv

ectio

n

nucl

eate

boi

ling

tran

sitio

n bo

iling

film

boi

ling

Regimes of Heat Transfer during Boiling

25.0T

radiation becomes important

There are correlations

for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

ฮ”๐‘‡ ๐‘‡ ๐‘‡

โ€œexcess temperatureโ€

Page 4: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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ยฉ Faith A. Morrison, Michigan Tech U.

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Heat Transfer with Phase Change

Because of high heat transfer rates and โ„Žmany engineering

devices operate in this regime

Geankoplis 4th ed, p284

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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For example: Nucleate boiling, horizontal surfaces

โ„Ž 1043 ฮ”T๐‘ž๐ด

16

โ„Ž 5.56 ฮ”T 16๐‘ž๐ด

240

ฮ”๐‘‡ ๐พ๐‘ž๐ด

๐‘˜๐‘Š๐‘š

โ„Ž๐‘Š๐‘š ๐พ

Equations good for

these units:

Regimes of Heat Transfer during Boiling

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

Page 5: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Geankoplis 4th ed, p285

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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For example: Nucleate boiling, vertical surfaces

โ„Ž 537 ฮ”T๐‘ž๐ด

3

โ„Ž 7.95 ฮ”T 3๐‘ž๐ด

63

ฮ”๐‘‡ ๐พ๐‘ž๐ด

๐‘˜๐‘Š๐‘š

โ„Ž๐‘Š๐‘š ๐พ

Equations good for

these units:

Regimes of Heat Transfer during Boiling

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

Geankoplis 4th ed, p285

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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For example: Nucleate boiling, forced convection inside tubes

โ„Ž 2.55ฮ”๐‘‡ ๐‘’

ฮ”๐‘‡ ๐พ๐‘ž๐ด

๐‘˜๐‘Š๐‘š

โ„Ž๐‘Š๐‘š ๐พ

๐‘ ๐‘˜๐‘ƒ๐‘Ž

Equations good for

these units:

Regimes of Heat Transfer during Boiling

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

Page 6: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Geankoplis 4th ed, p285

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

11

For example: Film boiling, horizontal tubes

โ„Ž 0.62๐‘˜ ๐œŒ ๐œŒ ๐œŒ ๐‘” ฮ”๐ป ๐‘‡ 0.4๐ถ , ฮ”๐‘‡

๐ท๐œ‡ ฮ”๐‘‡

ฮ”๐‘‡ ๐‘‡ ๐‘‡ ๐พ

โ„Ž๐‘Š๐‘š ๐พ

Equations good for these units:

๐‘˜

๐œŒ ,๐œŒ๐‘˜๐‘”๐‘š

ฮ”๐ป๐ฝ๐‘˜๐‘”

๐ท ๐‘š

๐œ‡ ๐‘ƒ๐‘Ž ๐‘ ๐‘” ๐‘š/๐‘ 

๐‘‡๐‘‡ ๐‘‡

2(All material properties at the film temperature)

Regimes of Heat Transfer during Boiling

Heat Transfer with Phase Changeฮ”๐‘‡ ๐‘‡ ๐‘‡

vapor phase

condensed phase

satT

heat

ยฉ Faith A. Morrison, Michigan Tech U.

12

Condensation

At low ฮ”๐‘‡, few droplets form,

As ฮ”๐‘‡ increases, more droplets form, increasing convection (flow).

Vertical plates; horizontal tubes important

๐‘‡ ๐‘‡

Heat Transfer with Phase Change-Condensationฮ”๐‘‡ ๐‘‡ ๐‘‡

Page 7: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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vapor phase

condensed phase

satTsatTT

Dropwise Condensation

heatโ€ขhigh hโ€ขhard to maintainโ€ขnot used in practice

ยฉ Faith A. Morrison, Michigan Tech U.

13There are correlations for h for each regime.

Heat Transfer with Phase Change-Condensationฮ”๐‘‡ ๐‘‡ ๐‘‡

vapor phase

condensed phase

satTsatTT

Film Condensation

heat

โ€ขfilm reduces hโ€ขvery stableโ€ขoften used

ยฉ Faith A. Morrison, Michigan Tech U.

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heat

There are correlations for h for each regime.

Heat Transfer with Phase Change-Condensationฮ”๐‘‡ ๐‘‡ ๐‘‡

Page 8: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Geankoplis 4th ed, p289

Regimes of Heat Transfer during Condensation

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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For example: Film condensation, vertical surfaces, laminar flow

๐‘๐‘ขโ„Ž๐ฟ๐‘˜

1.13๐œŒ ๐œŒ ๐œŒ ๐‘”ฮ”๐ป ๐‘‡ ๐ฟ

๐œ‡ ๐‘˜ ฮ”๐‘‡

ฮ”๐‘‡ ๐‘‡ ๐‘‡ ๐พ

โ„Ž๐‘Š๐‘š ๐พ

๐‘š๐‘˜๐‘”๐‘ 

Equations good for these units:

๐‘˜

๐œŒ ,๐œŒ๐‘˜๐‘”๐‘š

ฮ”๐ป๐ฝ๐‘˜๐‘”

๐ฟ ๐‘š

๐œ‡ ๐‘ƒ๐‘Ž ๐‘ ๐‘” ๐‘š/๐‘ 

๐‘‡๐‘‡ ๐‘‡

2(All material properties at the film temperature)

Re4๐‘š๐œ‹๐ท๐œ‡

1800

Heat Transfer with Phase Change-Condensation

Geankoplis 4th ed, p289

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

16

For example: Film condensation, vertical surfaces, turbulent flow

๐‘๐‘ขโ„Ž๐ฟ๐‘˜

0.0077๐œŒ ๐‘”L

๐œ‡Re .

โ„Ž๐‘Š๐‘š ๐พ

๐‘š๐‘˜๐‘”๐‘ 

Equations good for these units:

๐œŒ๐‘˜๐‘”๐‘š

๐ฟ ๐‘š

๐‘˜๐‘Š๐‘š

๐œ‡ ๐‘ƒ๐‘Ž ๐‘ ๐‘” ๐‘š/๐‘ 

๐‘‡๐‘‡ ๐‘‡

2(All material properties at the film temperature)

Re4๐‘š๐œ‹๐ท๐œ‡

1800

Regimes of Heat Transfer during Condensation

Heat Transfer with Phase Change-Condensation

Page 9: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Geankoplis 4th ed, p285

There are correlations for h for each regime.

ยฉ Faith A. Morrison, Michigan Tech U.

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For example: Film condensation, outside horizontal cylinders, laminar flow

๐‘๐‘ขโ„Ž๐ฟ๐‘˜

0.725๐œŒ ๐œŒ ๐œŒ ๐‘”ฮ”๐ป ๐‘‡ ๐ท

๐‘๐œ‡ ๐‘˜ ฮ”๐‘‡

ฮ”๐‘‡ ๐‘‡ ๐‘‡ ๐พ

โ„Ž๐‘Š๐‘š ๐พ

๐‘š๐‘˜๐‘”๐‘ 

๐‘‡ ๐พ

Equations good for these units:

๐‘˜

๐œŒ ,๐œŒ๐‘˜๐‘”๐‘š

ฮ”๐ป๐ฝ๐‘˜๐‘”

๐ท ๐‘š

๐œ‡ ๐‘ƒ๐‘Ž ๐‘ ๐‘” ๐‘š/๐‘ 

๐‘‡๐‘‡ ๐‘‡

2(All material properties at the film temperature)

Re4๐‘š๐œ‹๐ท๐œ‡

1800

Regimes of Heat Transfer during Condensation

Heat Transfer with Phase Change-Condensationฮ”๐‘‡ ๐‘‡ ๐‘‡

Evaporators

hot fluid (steam)

boiling liquor

steamsatT ,

liquorsatT ,

large heat-transfer resistance on liquor-side

hl

hs

negligible heat-transfer resistance due to wall

Issues:โ€ขviscosity, mโ€ขscale formationโ€ขliquor velocityโ€ขtime in evaporator

ยฉ Faith A. Morrison, Michigan Tech U.

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heat

Applied Heat Transfer with Phase Changeโ€”Evaporators

Page 10: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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steam

horizontal-tube evaporator

vertical-tube evaporator

โ€ขsteam in tubesโ€ขliquor on outsideโ€ขinexpensive, but poor liquid circulationโ€ขgood for non-depositing, low ๐œ‡fluids

โ€ขliquor in tubesโ€ขsteam on outsideโ€ขliquid circulates by natural convection

steamsteam

Geankoplis, p492

downcomer

โ€ขhydrostatic head in tubes prevents boiling in tubes

ยฉ Faith A. Morrison, Michigan Tech U.

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Applied Heat Transfer with Phase Changeโ€”Evaporators

steam

condensate

long-tube vertical evaporator

forced-circulation evaporator

โ€ขliquor in tubesโ€ขsteam on outsideโ€ขliquid circulates by natural convectionโ€ขsingle passโ€ขhigh liquid velocities

โ€ขliquor in tubesโ€ขsteam on outsideโ€ขliquid circulates by forced convectionโ€ขgood for high ๐œ‡ fluids

Geankoplis, p492ยฉ Faith A. Morrison, Michigan Tech U.

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Applied Heat Transfer with Phase Changeโ€”Evaporators

Page 11: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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non-boiling zone

boiling, 2-phase zone

Long-tube vertical evaporators

g

ยฉ Faith A. Morrison, Michigan Tech U.

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For discussion of how to estimate ๐‘ˆ, see Geankoplis 4th

edition, p533

Decreasing ๏ฟฝฬ…๏ฟฝ

Increasing ๐‘ฃ

Applied Heat Transfer with Phase Changeโ€”Evaporators

Greater efficiency may be obtained by operating several evaporators in series:

Multiple-Effect Evaporation

ยฉ Faith A. Morrison, Michigan Tech U.

22

1P 2P 3P

1T 2T 3T

fT

sT

Applied Heat Transfer with Phase Changeโ€”Evaporators

Page 12: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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ยฉ Faith A. Morrison, Michigan Tech U.

Applied Heat Transfer with Phase Changeโ€”Evaporators

Norbert Rillieux: Inventor of Multiple-Effect Evaporation

steam steam condensate

feed

vapor

concentrated liquor

bT

bT

bT

bT

fT

sT

Single-Effect Evaporators

ยฉ Faith A. Morrison, Michigan Tech U.

24

Applied Heat Transfer with Phase Changeโ€”Evaporators

Page 13: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Multiple-Effect Evaporators

For each effect the vapor product becomes the source of heat for the subsequent effect 321

321TTTPPP

1P 2P 3P

1T 2T 3T

fT

sT

ยฉ Faith A. Morrison, Michigan Tech U.

25(made white sugar possible)

pressure, temperature decrease

Applied Heat Transfer with Phase Changeโ€”Evaporators

3T

3T

fT

sT

3T

1P 2P 3P

1T 2T 3T

fT

sT

3TTUAQ s

323

212

11

TTUAqTTUAqTTUAq s

3TTUAqQ si

Compare Single- and Multiple-Effect Evaporators

same capacity = same amount of heat transferred(but we did not have to pay for it all = more efficient)

ยฉ Faith A. Morrison, Michigan Tech U.

26(used in sugar production, for example)

Applied Heat Transfer with Phase Changeโ€”Evaporators

Page 14: Heat Transfer with Phase Changefmorriso/cm310/lectures/2019 heat lecture 20 old heat 09.pdfFilm boiling, horizontal tubes โ„Ž 0.62 ๐‘˜ รฉ 7๐œŒ รฉ๐œŒ รŸ๐œŒ รฉ๐‘”ฮ”๐ป๐‘‡ รฆ ร”

Lecture 20 Applied Heat Transfer 2 CM3110 11/18/2019

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Boiling/Evaporation

โ€ข Industrially we operate either in nucleate boiling or film boiling regimes

โ€ข There are different correlations for each regime and for different geometries

Nucleate boiling, horizontal surfaces Nucleate boiling, vertical surfaces Nucleate boiling, forced convection Film boiling, horizontal tube

Condensation

โ€ข Industrially we operate in film condensation

โ€ข There are different correlations for different geometries

Vertical surfaces, laminar or turbulent Outside stack of horizontal cylinders

Evaporators โ€“ designed with the boiling regimes in mind

ยฉ Faith A. Morrison, Michigan Tech U.

27

Summary

Heat Transfer with Phase Change

ยฉ Faith A. Morrison, Michigan Tech U.28

Next:

โ€ข Heat transfer with phase changeโ€ข Evaporatorsโ€ข Radiationโ€ข DONE


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