Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

Kandlikar, Satish G.

doi:10.1080/01457630903304335

Cited by 72 publications

(26 citation statements)

References 39 publications

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“…While the physical mechanism responsible for the decrease in heat transfer coefficient in regime 'b' warrants further investigation, Kandlikar [26] suggested that formation of elongated bubbles and their passage over the microchannel walls have similarities to the bubble ebullition cycle in pool boiling; furthermore, he proposed that wall dryout occurs during the passage of elongated bubbles. For slug flow in microchannels, Jacobi and Thome [27] and Thome and Consolini [28] suggested that liquid thin film evaporation is the dominant heat transfer mode.…”

Section: Boiling Regime 'B'mentioning

confidence: 99%

Local heat transfer distribution and effect of instabilities during flow boiling in a silicon microchannel heat sink

Chen

Garimella

2011

International Journal of Heat and Mass Transfer

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Flow boiling of the perfluorinated dielectric fluid FC-77 in a silicon microchannel heat sink is investigated. The heat sink contains 60 parallel microchannels each of 100 m width and 389 m depth.Twenty-five evenly distributed temperature sensors in the substrate yield local heat transfer coefficients.The pressure drop across the channels is also measured. Experiments are conducted at five flow rates through the heat sink in the range of 20 to 80 ml/min with the inlet subcooling held at 26 K in all the tests.At each flow rate, the uniform heat input to the substrate is increased in steps so that the fluid experiences flow regimes from single-phase liquid flow to the occurrence of critical heat flux (CHF). In the upstream region of the channels, the flow develops from single-phase liquid flow at low heat fluxes to pulsating two-phase flow at high heat fluxes during flow instability that commences at a threshold heat flux in the range of 30.5 -62.3 W/cm² depending on the flow rate. In the downstream region, progressive flow patterns from bubbly flow, slug flow, elongated bubbles or annular flow, alternating wispy-annular and churn flow, and wall dryout at highest heat fluxes are observed. As a result, the heat transfer coefficients in the downstream region experience substantial variations over the entire heat flux range, based on which five distinct boiling regimes are identified. In contrast, the heat transfer coefficient midway along the channels remains relatively constant over the heat flux range tested. Due to changes in flow patterns during flow instability, the heat transfer is enhanced both in the downstream region (prior to extended wall dryout) and in the upstream region. A previous study by the authors found no effect of instabilities during flow boiling in a heat sink with larger microchannels (each 300 m wide and 389 m deep); it appears therefore that the effect of instabilities on heat transfer is amplified in smaller-sized channels.While CHF increases with increasing flow rate, the pressure drop across the channels has only a minimal † The experiments of this work were performed when the lead author was a Post-doctoral Researcher at Purdue University. BackgroundTwo-phase flow in microchannels provides higher performance than in single-phase operation while maintaining the wall temperature relatively uniform, and offers an attractive alternative for the cooling of high-power electronics. Although microchannel heat sinks have been extensively studied [ 1 , 2 ], understanding of two-phase thermal transport phenomena in microchannels is still limited due to their complexity.A number of studies have discussed the differences in flow boiling between small and large channels; a quantitative criterion was recently proposed for delineating micro-and macroscale behavior in twophase flow through microchannels [3]. For flow boiling in large channels, both convective and nucleate boiling heat transfer are considered important [4] and the overall heat transfer coefficient is a function of mass flow ...

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Section: Boiling Regime 'B'mentioning

confidence: 99%

Local heat transfer distribution and effect of instabilities during flow boiling in a silicon microchannel heat sink

Chen

Garimella

2011

International Journal of Heat and Mass Transfer

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“…In recent times reasonable success has been achieved in the modeling of boiling heat transfer in macro systems (Mukherjee and Dhir, 2004;Liao et al, 2004;Tomar et al, 2005;Genske and Stephan, 2006;Mukherjee and Kandilkar, 2007;Son and Dhir, 2008;Wu and Dhir;2010). This has been achieved by direct numerical simulation where separate set of conservation equations are solved for each of the phases and a suitable algorithm is adopted for the modeling of the interface.…”

Section: Gray Areas and Research Needsmentioning

confidence: 99%

“…Fig. 9 Dry patch formation in elongated bubble (Kandlikar 2010) At high mass flow rates vapor shear may overcome surface tension forces and succeed in removing the liquid film from the wall. For dryout to occur the average film thickness need not be zero, but the liquid film is wavy and the interfacial waves are large enough so that the troughs of them touch the wall.…”

Section: Figmentioning

confidence: 99%

Critical Heat Flux During Flow Boiling in Mini and Microchannel-a State of the Art Review

Das¹,

Chakraborty²,

Bhaduri³

2012

Frontiers in Heat and Mass Transfer

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A state of the art review of critical heat flux during flow boiling through mini and microchannels has been provided based on the open literature. This review mainly examines three aspects, namely the experimental investigations, the available correlations and the state of prediction using those correlations and finally the proposed physical mechanisms as well as the theoretical models. Before discussing the specific literature on microchannels, a brief overview of critical heat flux for pool and flow boiling is provided. The review has been concluded with a summary of the available information on this topic and the need for future research.

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“…Liquid film flow, which provides large heat flux at small temperature difference, deserves special attention in the analysis of heat transport in microscale systems [5]. Published methods for predicting the heat transfer with flow boiling in micro-scale heat exchangers are based either on certain modifications of models that characterize boiling in conventional tubes [1] or on specially developed correlations [3], but their application in various heat-exchange regimes was hardly a success. In particular, this applies to cryogenic compact heat exchangers operated at low mass and heat fluxes.…”

Section: Introductionmentioning

confidence: 99%

“…Two-phase compact heat exchangers offer ample opportunities for engineering applications such as high compact generators/condensers of power and cryogenic units and natural gas liquefaction units. The mechanisms of microscale heat transfer during flow boiling and condensation in mini/micro-channels were investigated, for example, in [1,2] and are fairly inconsistent especially for flow boiling. It has been found in a number of studies that heat transfer during flow boiling in mini-and microchannels is determined by the heat flux and depends only weakly on the mass flux [3].…”

Section: Introductionmentioning

confidence: 99%

Capillary hydrodynamics and transport processes during phase change in microscale systems

Kuznetsov

2017

J. Phys.: Conf. Ser.

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Abstract. The characteristics of two-phase gas-liquid flow and heat transfer during flow boiling and condensing in micro-scale heat exchangers are discussed in this paper. The results of numerical simulation of the evaporating liquid film flowing downward in rectangular minichannel of the two-phase compact heat exchanger are presented and the peculiarities of microscale heat transport in annular flow with phase changes are discussed. Presented model accounts the capillarity induced transverse flow of liquid and predicts the microscale heat transport processes when the nucleate boiling becomes suppressed. The simultaneous influence of the forced convection, nucleate boiling and liquid film evaporation during flow boiling in plate-fin heat exchangers is considered. The equation for prediction of the flow boiling heat transfer at low flux conditions is presented and verified using experimental data.

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Similarities and Differences Between Flow Boiling in Microchannels and Pool Boiling

Cited by 72 publications

References 39 publications

Local heat transfer distribution and effect of instabilities during flow boiling in a silicon microchannel heat sink

Local heat transfer distribution and effect of instabilities during flow boiling in a silicon microchannel heat sink

Critical Heat Flux During Flow Boiling in Mini and Microchannel-a State of the Art Review

Capillary hydrodynamics and transport processes during phase change in microscale systems

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