Flow Patterns and Heat Transfer for Flow Boiling in Small to Micro Diameter Tubes

Karayiannis, Tassos G.; Shiferaw, D.; Kenning, D. B. R.; Wadekar, Vishwas V.

doi:10.1080/01457630903311678

Cited by 36 publications

(9 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Also, heat transfer coefficients and boiling curves are independent of mass flux in the nucleate boiling region for a fixed channel size, but are affected by mass flux as convective boiling begins to dominate. Karayiannis et al [14] performed a study of flow boiling in tubes of hydraulic diameters ranging from 0.52 to 4.26 mm. They observed that boiling in the 0.52-mm tube was significantly more complex than that in larger tubes tested.…”

Section: Introductionmentioning

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

View full text Add to dashboard Cite

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 ...

show abstract

Section: Introductionmentioning

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

View full text Add to dashboard Cite

show abstract

“…(19) for a rough liquid film. This also could explain the fact that the 0.52-mm data were underpredicted in Figure 3e, in which flow patterns observed at the exit of the test tube indicated the occurrence of wavy film interfaces with relatively short wavelength [15,16]. Likewise, the reduction in pressure drop during the occurrence of dryout could be attributed to the decrease in shear stress due to the absence of film waves.…”

Section: Comparisons Of Homogeneous Flow and Three-zone Models With Datamentioning

confidence: 86%

“…The time-averaged wall shear stress and frictional pressure gradient are calculated from Eq. (16). This semimechanistic estimate replaces the fully homogeneous flow calculation, in which equivalent fluid properties are employed in Eq.…”

Section: Pressure Drop Modelmentioning

confidence: 99%

One-Dimensional Semimechanistic Model for Flow Boiling Pressure Drop in Small to Micro Passages

Shiferaw

Mahmoud

Karayiannis

et al. 2011

Heat Transfer Engineering

Self Cite

View full text Add to dashboard Cite

Accurate predictions of two-phase pressure drop in small to micro-diameter passages are necessary for the design of compact and ultra-compact heat exchangers, which find wide application in process and refrigeration industries and in the cooling of electronics. A semimechanistic model of boiling two-phase pressure drop in the confined bubble regime is formulated, following the three-zone approach for heat transfer. The total pressure drop is calculated by time-averaging the pressure drops for single-phase liquid, elongated bubble with a thin liquid film, and single-phase vapor. The model results were compared with experimental data collected for a wide range of tube diameters (4.26, 2.88, 2.02, 1.1, and 0.52 mm) for R134a at pressures of 6-12 bar. In this model's present form, its predictions are close to those of the homogeneous flow model but it provides a platform for further development.

show abstract

“…Significant disagreement in experimental trends and heat transfer mechanisms was reported in the literature for flow boiling in micro/minichannels, as provided in Karayiannis et al [5], Thome and Cioncolini [6], Li and Wu [7] and Wu et al [8]. Different trends for the local heat transfer coefficient h are observed by changing the vapor quality x, mass flux G, and heat flux q.…”

Section: Introductionmentioning

confidence: 85%

Heat Transfer Correlations for Elongated Bubbly Flow in Flow Boiling Micro/Minichannels

Sundén

2016

Heat Transfer Engineering

View full text Add to dashboard Cite

An improved conventional-to-micro/minichannel criterion was proposed by using the Bond number and the liquid Reynolds number. In micro/minichannels bubbles tend to be confined and elongated in the channel and the conventional two-phase flow theory loses its applicability. As significant disagreement in experimental trends and heat transfer mechanisms was reported for flow boiling in micro/minichannels in the literature, it is not possible to explain the discrepancy and predict all data points by a single correlation without considering the different flow patterns. In this study, heat transfer correlations for elongated bubbly flow in flow boiling micro/minichannels were developed based on a collected micro/minichannel heattransfer database. The newly developed correlations can not only present a decent overall accuracy, but also estimate the parametric trends correctly. Over 97% of the data points can be predicted by the proposed correlations within a ± 50% error band for elongated bubbly flow.Besides, a flow-pattern based model can be developed by combining the developed elongated bubbly flow correlations with previous annular flow correlations for predicting flow boiling heat transfer in micro/minichannels.

show abstract

Flow Patterns and Heat Transfer for Flow Boiling in Small to Micro Diameter Tubes

Cited by 36 publications

References 51 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

One-Dimensional Semimechanistic Model for Flow Boiling Pressure Drop in Small to Micro Passages

Heat Transfer Correlations for Elongated Bubbly Flow in Flow Boiling Micro/Minichannels

Contact Info

Product

Resources

About