Macro-to-microchannel transition in two-phase flow: Part 2 – Flow boiling heat transfer and critical heat flux

Ong, Chin Lee; Thome, John R.

doi:10.1016/j.expthermflusci.2010.12.003

Cited by 167 publications

(76 citation statements)

References 42 publications

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“…(17) and (18) Figure 3 Comparison of predicted heat transfer coefficient values with experimental results of (a) Sobierska et al [27], (b) Lee and Garimella [28], and (c) Qu and Mudawar [10]. …”

Section: Appendix Amentioning

confidence: 99%

“…As has been done in previous studies [11,17], a dryout condition is implemented whereby heat is assumed to be transferred directly to the vapor phase when the liquid film is thinner than the surface roughness of the channel walls. The single-phase heat transfer coefficient in driedout regions of the wall is calculated based on the average Nusselt number for the appropriate channel geometry assuming fully developed laminar flow in the vapor core.…”

Section: Heat Transfer Coefficientmentioning

confidence: 99%

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Mechanistic modeling of the liquid film shape and heat transfer coefficient in annular-regime microchannel flow boiling

Patel

Weibel

Garimella

2017

International Journal of Heat and Mass Transfer

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A methodology is proposed for predictive modeling of the liquid-gas interface shape and saturated flow boiling heat transfer coefficient in two-phase microchannel flows within the annular regime. The mechanistic model accounts for the effects of surface tension and interface curvature, gravity, and shear stress in determining the liquid film shape; one-dimensional conduction is assumed to occur across the variable-thickness film to calculate wall heat transfer coefficients locally along the channel length. Model performance is benchmarked against 251 experimentally measured heat transfer coefficient values taken from the literature for annularregime flow boiling in microchannels of a rectangular cross-section. These data are successfully predicted with a mean absolute error of 21.7%, and 72.1% of the points lie within an error band of ±30%. The match to data is poorest at lower vapor qualities corresponding to the onset of the annular regime, for which the heat transfer coefficient is underpredicted; an experimental investigation is performed to better understand the disparity under these operating conditions. Liquid film shapes are measured during adiabatic annular flow through microchannels of square cross-section for a range of channel hydraulic diameters (160 µm, 510 µm, 1020 µm) and operating conditions, so as to control the void fraction and Weber number of the flow. Using air and water as the working gas and liquid, respectively, trends in film behavior are identified and 2 compared against model predictions. The experimental findings reveal the non-negligible impact of capillary pumping on the interface morphology at the onset of the annular regime.

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Section: Appendix Amentioning

confidence: 99%

Section: Heat Transfer Coefficientmentioning

confidence: 99%

Mechanistic modeling of the liquid film shape and heat transfer coefficient in annular-regime microchannel flow boiling

Patel

Weibel

Garimella

2017

International Journal of Heat and Mass Transfer

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“…Texture-based image processing techniques are employed in order to resolve boundaries between the liquid phase, which contains the seeding particles, and the gas phase with an accuracy of ±2.8 μm at a magnification of 10× or ±6.7 μm at a magnification of 4× [15]. The resulting accuracy of corner film thickness measurements considered in the present study ranges from 2.5% to 6.8%; for the purpose of developing a model, Imaging is performed at discrete depths within the lower half of the channel cross-section and the bubbles are assumed to be unaffected by gravity (i.e., vertically symmetric) based on a confinement-number transition criterion from the literature [21]. Ong and Thome [21] performed visualizations to investigate gravitational effects on flow morphology in small-scale channels and found that flows with Co greater than 1 were unaffected by buoyancy forces.…”

Section: Imaging and Interface Characterizationmentioning

confidence: 99%

“…The resulting accuracy of corner film thickness measurements considered in the present study ranges from 2.5% to 6.8%; for the purpose of developing a model, Imaging is performed at discrete depths within the lower half of the channel cross-section and the bubbles are assumed to be unaffected by gravity (i.e., vertically symmetric) based on a confinement-number transition criterion from the literature [21]. Ong and Thome [21] performed visualizations to investigate gravitational effects on flow morphology in small-scale channels and found that flows with Co greater than 1 were unaffected by buoyancy forces. For the two test sections in the present study, Co = 2.7 for Dh = 1020 μm and Co = 5.4 for Dh = 510 μm.…”

Section: Imaging and Interface Characterizationmentioning

confidence: 99%

Characterization of liquid film thickness in slug-regime microchannel flows

Patel

Weibel

Garimella

2017

International Journal of Heat and Mass Transfer

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An experimental investigation is conducted to examine the effects of operating conditions and channel size on the liquid film thickness of vapor bubbles in adiabatic air-water flows within the slug flow regime. Acrylic test sections are fabricated to contain a single microchannel of square cross-section with hydraulic diameters of 510 μm and 1020 μm. High-speed visualizations are used to map the flow regimes in these channels in order to determine the range of liquid and gas flow rates for which slug-regime flows are sustained. Subsequently, a tomographic optical imaging technique is employed to quantitatively reconstruct the liquid-gas interface of vapor bubbles at selected operating conditions. This technique relies on visualization of fluorescent particles seeded into the liquid phase in order to identify the phase boundaries within thin sections of the flow. Using the reconstructions, the thickness of the liquid film in the corner of the square channel cross-section is extracted. This film thickness is found to decrease with increasing capillary number, and a simple expression is proposed for calculation of the film thickness; predictions from this model match the measurements with a mean absolute error (MAE) of 21.6%; 85.7% of all predicted data points fall within an error band of ±30%. Additionally, film thickness data from the literature are compared to model predictions and a comparable MAE of 21.8% is found with 77.8% of data points falling within an error band of ±30%.

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“…The opposite trend was addressed for high heat flux conditions. Ong and Thome (2011b) experimentally investigated flow boiling heat transfer of t hree refrigerants in channels of 1.03, 2.20 and 3.04 mm diameters. R-134a, R-236fa and R-245fa were used as working fluids in their study.…”

Section: Two-phase Heat Transfermentioning

confidence: 99%

A Critical Review of Recent Investigations on Flow Pattern and Heat Transfer During Flow Boiling in Micro-Channels

Saisorn¹

2012

Frontiers in Heat and Mass Transfer

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Macro-to-microchannel transition in two-phase flow: Part 2 – Flow boiling heat transfer and critical heat flux

Cited by 167 publications

References 42 publications

Mechanistic modeling of the liquid film shape and heat transfer coefficient in annular-regime microchannel flow boiling

Mechanistic modeling of the liquid film shape and heat transfer coefficient in annular-regime microchannel flow boiling

Characterization of liquid film thickness in slug-regime microchannel flows

A Critical Review of Recent Investigations on Flow Pattern and Heat Transfer During Flow Boiling in Micro-Channels

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