Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel?Channel classification Need for smaller passages FLOW BOILING IN MICROCHANNELS Ajith Krishnan R Govt. Engineering College Kozhikode High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern November 27, 2013 Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27, 2013 1 / 32 Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Contents 1 2 High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies 3 Boiling Heat Transfer Types of Boiling Heat Transfer 4 Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern 5 Conclusion Conclusion 6 References References Ajith Krishnan R (GEC KKD) What is a MicroChannel? Channel classification Need for smaller passages High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Flow boiling in Microchannels November 27, 2013 2 / 32 What is a MicroChannel? Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Channel classification Channel classification High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Figure: Channel Classification[1] • D is the channel diameter • In the case of non-circular channels D is the minimum Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) channel dimension Flow boiling in Microchannels November 27, 2013 3 / 32 2013 4 / 32 References References Ajith Krishnan R (GEC KKD) .What is a MicroChannel? Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Need for smaller passages Need for smaller passages High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Variation of the heat transfer coefficient with channel size for fully developed laminar flow of air and water [1] Flow boiling in Microchannels November 27. 2013 5 / 32 References References Ajith Krishnan R (GEC KKD) .What is a MicroChannel? Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Need for smaller passages Need for smaller passages High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Variation of pressure gradient with channel size for fully developed laminar flow of air and water [1] Flow boiling in Microchannels November 27. having flow channels having capillary dimensions 4µ Flow boiling in Microchannels November 27.What is a MicroChannel? Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Need for smaller passages Need for smaller passages • Dramatic Enhancement in ”h” with a reuction in Channel Size is Clear • Pressure Gradient increases with reduction in Channel Size 1 • Compactness /AreaDensity = SurfaceArea ∝D Volume High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer • Decrease in channel size(D) cause an increase in Area Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Density or Compactness • Most efficient heat and mass transfer processes occur Conclusion Conclusion inside the lungs and kidney. 2013 6 / 32 References References Ajith Krishnan R (GEC KKD) . High Heat Flux Removal Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Classification of High Heat Flux Classification of High Heat Flux • Heat flux from microprocessors will be a great challenge in thermal managemnt • Electronic devices particularly high power defence High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies elecronics dissipate 1000W /cm2 and higher • In future 2500W /cm2 could be reached Boiling Heat Transfer Types of Boiling Heat Transfer Classify High Heat Fluxes as: — High Heat Flux(HHF)::102 − 103 W /cm2 —Ultra High Heat Flux(UHF)::103 − 104 W /cm2 — Extreme Heat Flux(UHF)::> 104 W /cm2 Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 7 / 32 . Emerging technology High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Rest of all technologies associated with three basic types of coolant flows: –Microchannels –Jet impingement –Sparys Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27.High Heat Flux Removal Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages High Heat Flux Removal Technologies High Heat Flux Removal Technologies • Liquid as working medium/ With and with out phase change • Heat Pipe -Successful heat removal technology • Nano fluids. 2013 8 / 32 . Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Types of Boiling Heat Transfer High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Figure: Classification of boiling on the basis of the presence of bulk fluid motion[3] Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Pool Boiling-in the absence of bulk fluid flow Flow Boiling or Forced Convection Boiling-in the presence of bulk fluid flow Flow boiling in Microchannels November 27. 2013 9 / 32 Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) . Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Subcooled and Saturated Boiling High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Figure: Classification of boiling on the basis of the presence of bulk liquid temperature [3] • Pool and flow boiling are further classified as subcooled Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion boiling or saturated boiling. 2013 10 / 32 References References Ajith Krishnan R (GEC KKD) .depending on the bulk liquid temperature • Subcooled boiling-the bulk of the liquid is subcooled • Saturated boiling-the bulk of the liquid is saturated Flow boiling in Microchannels November 27. Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Pool Boiling Curve High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Figure: Pool Boiling Curve For water at Atmospheric pressure[4] Flow boiling in Microchannels November 27. 2013 11 / 32 . Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Pool Boiling Regimes High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: The Various stages in pool boiling curve[4] References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 12 / 32 . 2013 13 / 32 .Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Actual Pool Boiling Curve High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Actual pool boiling curve[3] References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 14 / 32 References References Ajith Krishnan R (GEC KKD) .Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Flow Boiling/Convective Boiling High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Regions of Heat Transfer in Convectivel boiling [4] Flow boiling in Microchannels November 27. 2013 15 / 32 References References Ajith Krishnan R (GEC KKD) .Boiling Heat Transfer Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Types of Boiling Heat Transfer Boiling Map High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Variation of heat transfer coefficient with Quality with increasing Heat flux as a parameter[4] Flow boiling in Microchannels November 27. 2013 16 / 32 .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Boiling in a Microchannel Flow Boiling in a Microchannel • Flow boiling in a channel is nothing but boiling occurring High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies due the flow of a liquid with certain velocity whose walls are subjected to heat • Microchannel flows are driven by pumps with mean flow Boiling Heat Transfer Types of Boiling Heat Transfer velocities in the range of few millimeters per second to many 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 Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 17 / 32 .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Boiling in a Microchannel Microchannel Vs Conventional Channel • The 2 phase heat transfer correlations for microchannels High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies are different from conventional channels • Surface tension forces are more dominant and gravity Boiling Heat Transfer Types of Boiling Heat Transfer forces are negligible in microchannels • Separate studies need to be conducted for microchannels Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 18 / 32 .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Two Phase Flow Basic Definitions and Terminology High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 19 / 32 .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Two Phase Flow Basic Definitions and Terminology High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. flow.Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Need For Identifying The Flow Patterns • Heat tansfer coefficients and pressure drop are closely related to the local two phase flow structure of the fluid • Flow pattern prediction is an important aspect in High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies modelling evaporation and condensation • Flow pattern depends on the conditions of Boiling Heat Transfer Types of Boiling Heat Transfer pressure.heat flux.and channel geometry • Physical parameters delinating the flow pattern are Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern –Surface tension –Gravity(non vertical channels-stratification) Flow boiling in Microchannels November 27. 2013 20 / 32 Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) . Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern in vertical tube with out heating High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Figure: Two phase flow pattern in vertical up flow[5] Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 21 / 32 . Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern in vertical heated Channels High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Two phase flow pattern in vertical Evaporator Tube[5] Flow boiling in Microchannels November 27. 2013 22 / 32 References References Ajith Krishnan R (GEC KKD) . 2013 23 / 32 References References Ajith Krishnan R (GEC KKD) .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern in Horizontal Channels Without Heating High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Flow pattern in Horizontal Flow[5] Flow boiling in Microchannels November 27. Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern in Horizontal Heated Tube High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Figure: Flow pattern in Horizontal tube With Heating[5] Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. 2013 24 / 32 . 2013 25 / 32 References References Ajith Krishnan R (GEC KKD) .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern Map in Horizontal Two Phase Flow High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Baker Flow Pattern Map for Horizontal Flow in a Pipe[4] Flow boiling in Microchannels November 27. 2013 26 / 32 References References Ajith Krishnan R (GEC KKD) .Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Flow pattern Map in Verticall Two Phase Flow High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Hewitt and Roberts Flow Pattern Map for Vertical Upflow in a Pipe[4] Flow boiling in Microchannels November 27. Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Bubble Nucleation -Nucleation Sites? Different Routes for Nucleation • Deviation from Stable equillibrium • Deviation from Metastable equillibrium • Deviation from Unstable equillibrium High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Metastable state[4] Flow boiling in Microchannels November 27. 2013 27 / 32 References References Ajith Krishnan R (GEC KKD) . Flow Boiling In Microchannels Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Flow Pattern Heat Transfer Mechanisms During Flow Boiling In Microchannel -Nucleate Boiling-HHF and low vapour quality -Convective Boiling-High mass flux and high vapour quality High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion Figure: Different heat transfer mechanis ms during flow boiling in a microchannel Flow boiling in Microchannels November 27. 2013 28 / 32 References References Ajith Krishnan R (GEC KKD) . 2013 29 / 32 .Conclusion Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages Conclusion Conclusion • Fundamental understanding of flow boiling phenomenon in microchannel is slowely emerging • Understanding of liquid and vapour phase interactions High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies during 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 for Boiling Heat Transfer Types of Boiling Heat Transfer different channel types • Flow reversal in multichannels.Rapod expansion of bubble Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern in to slug pushes liquid away both upstream and downstream of the flow Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27. X. 2013 30 / 32 High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) . Thome Wolverine Engineering Data Book III Wolverine tube inc Flow boiling in Microchannels November 27. Vol. Stephane Colin. King Heat Transfer And Fluid Flow In Minichannels And Microchannels ELSEVIER. Michael R.References Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages References References [1]Satish G. John R. A. Second edition 2006 [4]John G.1994 [5]. Cengel HEAT TRANSFER A Practical Approach McGraw-Hill. Lin A Review of High-Heat-Flux Heat Removal Technologies Journal of Heat Transfer. Thome Convective Boiling and Condensation Oxford University Press. Collier. Third Edition.NOVEMBER 2011. 133/ 110801-1 [3]Yunus A. First edition 2006 [2]M. Ebadian. Dongqing Li. Srinivas Garimella. John R. Kandlikar.C. 126. Vol.References Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages References References High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies [6]. 2013 31 / 32 .ASME. pp. 8.Kandlikar. Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27.16.G. S. Heat Transfer Mechanisms During Flow Bo iling in Microchannels Journal of Heat Transfer. 2013 32 / 32 .Flow boiling in Microchannels Ajith Krishnan R What is a MicroChannel? Channel classification Need for smaller passages High Heat Flux Removal Classification of High Heat Flux High Heat Flux Removal Technologies Thank you Boiling Heat Transfer Types of Boiling Heat Transfer Flow Boiling In Microchannels Flow Boiling in a Microchannel Two Phase Flow Flow Pattern Conclusion Conclusion References References Ajith Krishnan R (GEC KKD) Flow boiling in Microchannels November 27.