Forced convective boiling heat transfer in microtubes at low mass and heat fluxes

Yen, Tzu-Hsiang; Kasagi, Nobuhide; Suzuki, Yuji

doi:10.1016/j.ijmultiphaseflow.2003.09.004

Cited by 163 publications

(70 citation statements)

References 20 publications

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“…The decrease in heat transfer coefficient with increasing heat flux observed here was also reported in [7,8], and the behavior was attributed to a large local vapor quality at a higher heat flux. 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.…”

supporting

confidence: 84%

“…[6], and was found to be independent of mass flow rate and to decrease with increasing local vapor quality as the flow propagates downstream [7,8,9]. Piasecka et al [10] showed that initiation of boiling in a narrow channel causes a sharp drop in the wall temperature and the boiling extends upstream as the heat flux is increased.…”

Section: Introductionmentioning

confidence: 99%

“…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 rate, heat flux, and vapor quality [5]. In contrast, the heat transfer coefficient during flow boiling in microchannels can be well predicted by correlations proposed for nucleate boiling heat transfer[6], and was found to be independent of mass flow rate and to decrease with increasing local vapor quality as the flow propagates downstream [7,8,9]. Piasecka et al [10] showed that initiation of boiling in a narrow channel causes a sharp drop in the wall temperature and the boiling extends upstream as the heat flux is increased.…”

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confidence: 99%

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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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supporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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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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“…Vertrel XF with a saturation temperature of 52°C was used as the working fluid in their study. Steinke and Kandlikar [8] and Yen et al [9] studied the flow boiling of water and refrigerants (HCFC123, FC72) respectively. They also reported that the heat transfer coefficient decreases monotonically with an increase in vapor quality, in agreement with the earlier studies.…”

Section: Introductionmentioning

confidence: 99%

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

Singh

Bhide

Duttagupta

et al. 2009

IEEE Trans. Comp. Packag. Technol.

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Abstract-This paper focuses on experimentally studying the pressure drop characteristics for two-phase flow in microchannels of hydraulic diameter 109 μm, over a relatively large range of heat flux of (0-30 W/cm 2 ) and mass flow rate values (44-1114 kg/m 2 -s). Three fluid flow regimes (single-phase, twophase, and dryout) have been covered in this paper, with deionized water as the working fluid. For a given heat flux, the variation of average pressure drop with flow rate can be classified into three distinct regimes. In the first regime (higher flow rate), the pressure drop decreases linearly with decrease in flow rate. In the second regime (lower flow rate), pressure drop increases with decreasing flow rate and reaches a maximum (with a minimum on either side). Finally, in the very low flow rate regime, pressure drop increases rapidly with decreasing flow rate. The average pressure drop in the two-phase regime is predicted well by the annular flow model. In addition to absolute pressure drop values, we also report pressure fluctuations. The magnitude of pressure fluctuations appears to be correlated to the underlying flow regime, such as bubbly, slug, and annular regimes, which have been identified through the flow visualization. An important outcome of this study is the identification of as many as four operating points with similar pressure drop penalty. This may help to choose the right operating conditions for a microchannelbased heat sink for use in cooling electronics. These detailed experimental results are also expected to be useful for modeling two-phase flow in microchannels.

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“…Heat transfer characteristics for saturated boiling were considered by Yen et al [31]. From this study of convective boiling of HCFC123 and FC72 in micro-tubes with inner diameter 190, 300 and 510 µm one can see that in the saturated boiling regime, the heat transfer coefficient monotonically decreased with increasing vapour quality, but is independent of mass flux.…”

Section: Heat Transfermentioning

confidence: 83%

Boiling in micro-channels

Hetsroni¹

2010

Bulletin of the Polish Academy of Sciences: Technical Sciences

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Abstract. Boiling heat transfer in micro-channels is a subject of intense academic and practical interest. Though many heat transfer correlations have been proposed, most were empirically formulated from experimental data. However, hydrodynamic and thermal aspects of boiling in micro-channels are not well understood. Moreover, there are only a few theoretical models that link the heat transfer mechanism with flow regimes in micro-channels. Also, there are discrepancies between different sets of published results, and heat transfer coefficients have either well exceeded, or fallen far below, those predicted for conventional channels. Here we consider these problems with regard to micro-channels with hydraulic diameters ranging roughly from 5 µm to 500 µm, to gain a better understanding of the distinct properties of the measurement techniques and uncertainties, the conditions under which the experimental results should be compared to analytical or numerical predictions, boiling phenomenon, as well as different types of micro-channel heat sinks. Two-phase flow maps and heat transfer prediction methods for vaporization in macro-channels are not applicable in micro-channels, because surface tension dominates the phenomena, rather than gravity forces. The models of convection boiling should correlate the frequencies, sizes and velocities of the bubbles and the coalescence processes, which control the flow pattern transitions, together with the heat flux and the mass flux. Therefore, the vapour bubble size distribution must be taken into account. The flow pattern in parallel micro-channels is quite different from that in a single micro-channel. At same values of heat and mass flux, different, time dependent, flow regimes occur in a given micro-channel. At low vapour quality, heat flux causes a sudden release of energy into the vapour bubble, which grows rapidly and occupies the entire channel cross section. The rapid bubble growth pushes the liquid-vapour interface on both caps of the vapour bubble, at the upstream and the downstream ends, and leads to a reverse flow. We term this phenomenon as explosive boiling. One of the limiting operating conditions with flow boiling is the critical heat flux (CHF). The CHF phenomenon is different from that observed in conventional size channels.

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Forced convective boiling heat transfer in microtubes at low mass and heat fluxes

Cited by 163 publications

References 20 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

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

Boiling in micro-channels

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