flow boiling in microchannel

8/13/2019 Flow Boiling in Microchannel

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Flow boiling inMicrochannels

Ajith KrishnanR

What is a Mi-croChannel?

Channelclassification

Need for smallerpassages

High HeatFlux Removal

Classification ofHigh Heat Flux

High Heat FluxRemovalTechnologies

Boiling HeatTransfer

Types of BoilingHeat Transfer

Flow BoilingInMicrochannels

Flow Boiling in aMicrochannel

Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

FLOW BOILING IN MICROCHANNELS

Ajith Krishnan R

Govt. Engineering College Kozhikode

November 27, 2013

Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 1 / 32


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Ajith KrishnanR





Classification ofHigh Heat Flux

High Heat FluxRemovalTechnologies





Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

Contents

1 What is a MicroChannel?

Channel classificationNeed for smaller passages

2 High Heat Flux RemovalClassification of High Heat FluxHigh Heat Flux Removal Technologies

3 Boiling Heat TransferTypes of Boiling Heat Transfer

4 Flow Boiling In MicrochannelsFlow Boiling in a Microchannel

Two Phase FlowFlow Pattern

5 ConclusionConclusion

6 References

References



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Classification ofHigh Heat FluxHigh Heat FluxRemovalTechnologies





Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

What is a MicroChannel? Channel classification

Channel classification

Figure: Channel Classification[1]

D is the channel diameter

In the case of non-circular channels D is the minimum

channel dimension



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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

What is a MicroChannel? Need for smaller passages

Need for smaller passages

Figure: Variation of the heat transfer coefficient with channel size forfully developed laminar flow of air and water [1]



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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References



Figure: Variation of pressure gradient with channel size for fullydeveloped laminar flow of air and water [1]



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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References



Dramatic Enhancement in h with a reuction in ChannelSize is Clear

Pressure Gradient increases with reduction in Channel Size

Compactness/AreaDensity= SurfaceAreaVolume

1D

Decrease in channel size(D) cause an increase in AreaDensity or Compactness

Most efficient heat and mass transfer processes occurinside the lungs and kidney, having flow channels havingcapillary dimensions 4


Hi h H Fl R l Cl ifi i f Hi h H Fl


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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

High Heat Flux Removal Classification of High Heat Flux

Classification of High Heat Flux

Heat flux from microprocessors will be a great challenge inthermal managemnt

Electronic devices particularly high power defenceelecronics dissipate 1000W/cm2 and higher

In future 2500W/cm2 could be reached

Classify High Heat Fluxes as:

High Heat Flux(HHF)::102 103W/cm2

Ultra High Heat Flux(UHF)::103 104W/cm2

Extreme Heat Flux(UHF)::>104W/cm2


Hi h H t Fl R l Hi h H t Fl R l T h l i


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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

High Heat Flux Removal High Heat Flux Removal Technologies

High Heat Flux Removal Technologies

Liquid as working medium/ With and with out phasechange

Heat Pipe -Successful heat removal technology

Nano fluids- Emerging technology

Rest of all technologies associated with three basic types ofcoolant flows:

Microchannels

Jet impingement

Sparys


Boiling Heat Transfer Types of Boiling Heat Transfer


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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References


Types of Boiling Heat Transfer

Figure: Classification of boiling on the basis of the presence of bulkfluid motion[3]

Pool Boiling-in the absence of bulk fluid flow

Flow Boiling or Forced Convection Boiling-in the presence

of bulk fluid flowAjith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 9 / 32



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Classification of

High Heat FluxHigh Heat FluxRemovalTechnologies





Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References


Subcooled and Saturated Boiling

Figure: Classification of boiling on the basis of the presence of bulkliquid temperature [3]

Pool and flow boiling are further classified as subcooledboiling or saturated boiling,depending on the bulk liquidtemperature

Subcooled boiling-the bulk of the liquid is subcooled

Saturated boiling-the bulk of the liquid is saturatedAjith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 10 / 32



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Classification of






Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References


Pool Boiling Curve

Figure: Pool Boiling Curve For water at Atmospheric pressure[4]Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 11 / 32



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Classification of






Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References


Pool Boiling Regimes

Figure: The Various stages in pool boiling curve[4]




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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

References

References

g yp g

Actual Pool Boiling Curve

Figure: Actual pool boiling curve[3]




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Two Phase Flow

Flow Pattern

Conclusion

Conclusion

ReferencesReferences

g y g

Flow Boiling/Convective Boiling

Figure: Regions of Heat Transfer in Convectivel boiling [4]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Boiling Map

Figure: Variation of heat transfer coefficient with Quality with

increasing Heat flux as a parameter[4]Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 15 / 32

Flow Boiling In Microchannels Flow Boiling in a Microchannel


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow Boiling in a Microchannel

Flow boiling in a channel is nothing but boiling occurringdue the flow of a liquid with certain velocity whose wallsare subjected to heat

Microchannel flows are driven by pumps with mean flowvelocities in the range of few millimeters per second tomany centimeters per second

Flow in microchannels will be mainly laminar

Two Phase flow With Phase Change


Flow Boiling In Microchannels Flow Boiling in a Microchannel


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Microchannel Vs Conventional Channel

The 2 phase heat transfer correlations for microchannelsare different from conventional channels

Surface tension forces are more dominant and gravityforces are negligible in microchannels

Separate studies need to be conducted for microchannels


Flow Boiling In Microchannels Two Phase Flow


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Basic Definitions and Terminology


Flow Boiling In Microchannels Two Phase Flow


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Basic Definitions and Terminology


Flow Boiling In Microchannels Flow Pattern


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Need For Identifying The Flow Patterns

Heat tansfer coefficients and pressure drop are closelyrelated to the local two phase flow structure of the fluid

Flow pattern prediction is an important aspect inmodelling evaporation and condensation

Flow pattern depends on the conditions ofpressure,flow,heat flux,and channel geometry

Physical parameters delinating the flow pattern are

Surface tension

Gravity(non vertical channels-stratification)




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern in vertical tube with out heating

Figure: Two phase flow pattern in vertical up flow[5]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern in vertical heated Channels

Figure: Two phase flow pattern in vertical Evaporator Tube[5]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern in Horizontal Channels WithoutHeating

Figure: Flow pattern in Horizontal Flow[5]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern in Horizontal Heated Tube

Figure: Flow pattern in Horizontal tube With Heating[5]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern Map in Horizontal Two PhaseFlow

Figure: Baker Flow Pattern Map for Horizontal Flow in a Pipe[4]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Flow pattern Map in Verticall Two PhaseFlow

Figure: Hewitt and Roberts Flow Pattern Map for Vertical Upflow ina Pipe[4]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Bubble Nucleation

-Nucleation Sites?

Different Routes for Nucleation Deviation from Stable equillibrium Deviation from Metastable equillibrium Deviation from Unstable equillibrium

Figure: Metastable state[4]




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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Heat Transfer Mechanisms During FlowBoiling In Microchannel

-Nucleate Boiling-HHF and low vapour quality-Convective Boiling-High mass flux and high vapour quality

Figure: Different heat transfer mechanis ms during flow boiling in amicrochannel


Conclusion Conclusion


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Conclusion

Fundamental understanding of flow boiling phenomenon inmicrochannel is slowely emerging

Understanding of liquid and vapour phase interactionsduring two phase flow in microchannel have intense

important Surface tension is the dominant force in flow field

Need of an acurate experimental flow boiling data need fordifferent channel types

Flow reversal in multichannels.Rapod expansion of bubblein to slug pushes liquid away both upstream anddownstream of the flow


References References


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Ajith KrishnanR





Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


References

[1]Satish G. Kandlikar, Srinivas Garimella, Dongqing Li, Stephane

Colin, Michael R. KingHeat Transfer And Fluid Flow In Minichannels And Microchannels

ELSEVIER. First edition 2006

[2]M. A. Ebadian,C. X. Lin

A Review of High-Heat-Flux Heat Removal Technologies

Journal of Heat Transfer,NOVEMBER 2011, Vol. 133/ 110801-1

[3]Yunus A. Cengel

HEAT TRANSFER A Practical Approach

McGraw-Hill. Second edition 2006

[4]John G. Collier, John R. Thome

Convective Boiling and Condensation

Oxford University Press, Third Edition,1994

[5], John R. Thome

Wolverine Engineering Data Book III

Wolverine tube incAjith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 30 / 32

References References


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Ajith KrishnanR





Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


References

[6],Kandlikar, S.G.

Heat Transfer Mechanisms During Flow Bo iling in Microchannels

Journal of Heat Transfer,ASME, Vol. 126, pp. 8- 16.


Fl b ili i


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Classification of




Flow Boiling

InMicrochannels


Two Phase Flow

Flow Pattern

Conclusion

Conclusion


Thank you


flow boiling in microchannel

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