Transport Phenomena in Two-Phase Micro-Channel Heat Sinks

The design and reliable operation of a two-phase micro-channel heat sink require a fundamental understanding of the complex transport phenomena associated with convective boiling in small, parallel coolant passages. This understanding is the primary goal of this paper. This goal is realized by exploring the following aspects of boiling in micro-channels: hydrodynamic instability, two-phase flow patterns, pressure drop, and convective boiling heat transfer. High-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities. Two types of dynamic instability were identified, a severe pressure drop oscillation and a mild parallel channel instability, and a simple method is recommended to completely suppress the former. Predictions of three popular two-phase pressure drop models and correlations were compared to micro-channel water data, and only a separated flow (Lockhart-Martinelli) correlation based on the assumption of laminar flow in both phases gave acceptable predictions. Several popular heat transfer correlations were also examined and deemed unsuitable for micro-channel heat sinks because all these correlations are based on turbulent flow assumptions, and do not capture the unique features of micro-channel flow such as abrupt transition to slug flow, hydrodynamic instability, and high droplet entrainment in the annular regime. These findings point to the need for further study of boiling behavior and new predictive tools specifically tailored to micro-channel heat sinks.

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Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

Heat Transfer: Volume 3 ◽

10.1115/ht2003-47050 ◽

2003 ◽

Cited By ~ 2

Author(s):

Weilin Qu ◽

Seok-Mann Yoon ◽

Issam Mudawar

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Flow Pattern ◽

Two Phase Flow ◽

Flow Patterns ◽

Heat Sinks ◽

Phase Flow ◽

Micro Channel ◽

Two Phase ◽

Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

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Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

Journal of Electronic Packaging ◽

10.1115/1.1756589 ◽

2004 ◽

Vol 126 (3) ◽

pp. 288-300 ◽

Cited By ~ 16

Author(s):

Weilin Qu ◽

Seok-Mann Yoon ◽

Issam Mudawar

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Flow Pattern ◽

Two Phase Flow ◽

Flow Boiling ◽

Flow Patterns ◽

Heat Sinks ◽

Phase Flow ◽

Micro Channel ◽

Two Phase

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406×2.032mm2 cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Features unique to two-phase micro-channel flow were identified and employed to validate key assumptions of an annular flow boiling model that was previously developed to predict pressure drop and heat transfer in two-phase micro-channel heat sinks. This earlier model was modified based on new findings from the adiabatic two-phase flow study. The modified model shows good agreement with experimental data for water-cooled heat sinks.

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Generalized Two-Phase Pressure Drop and Heat Transfer Correlations in Evaporative Micro/Mini-Channels

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1 ◽

10.1115/ht2007-32157 ◽

2007 ◽

Cited By ~ 3

Author(s):

Hee Joon Lee ◽

Dongyao Liu ◽

Shi-Chune Yao ◽

Y. Alyousef

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Bond Number ◽

Micro Channel ◽

Two Phase ◽

Working Fluids ◽

Operational Conditions ◽

Micro Channels ◽

Wide Range ◽

Existing Data

Existing data base and correlations in literature on the micro-channel pressure drop and heat transfer are reviewed. None of the existing correlations can cover the wide range of working fluids, operational conditions and different microchannel dimensions. The importance of the Bond number, which relates the nominal bubble dimension or capillary parameter with the channel size, is revealed. Using the Bond number, improved correlations of pressure drop and heat transfer are established. The new correlations predict the existing data well over wide ranges of working fluids, operational conditions and dimensions of micro-channels. Furthermore, Bond number could be used as a criterion to classify a flow path as a micro-channel or conventional macro-channel.

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Fluid flow and heat transfer characteristics of low temperature two-phase micro-channel heat sinks – Part 2. Subcooled boiling pressure drop and heat transfer

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2008.02.013 ◽

2008 ◽

Vol 51 (17-18) ◽

pp. 4327-4341 ◽

Cited By ~ 42

Author(s):

Jaeseon Lee ◽

Issam Mudawar

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Pressure Drop ◽

Low Temperature ◽

Heat Sinks ◽

Micro Channel ◽

Subcooled Boiling ◽

Heat Transfer Characteristics ◽

Two Phase ◽

Flow And Heat Transfer

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Convective Boiling in Parallel Micro-Channels

1st International Conference on Microchannels and Minichannels ◽

10.1115/icmm2003-1007 ◽

2003 ◽

Cited By ~ 12

Author(s):

G. Hetsroni ◽

D. Klein ◽

A. Mosyak ◽

Z. Segal ◽

E. Pogrebnyak

Keyword(s):

Heat Flux ◽

High Speed ◽

Heat Sinks ◽

Micro Channel ◽

Clear Water ◽

Two Phase ◽

Convective Boiling ◽

Flow Rates ◽

Micro Channels ◽

Infrared Radiometry

Experiments were performed with clear water and with surfactant flowing in parallel triangular micro-channels. The study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. Different flow patterns were observed simultaneously in various micro-channels at a fixed value of water or surfactant flow rates. Depending on flow and heat flux, pressure and temperature instabilities in the heated micro-channels were studied. This work develops a practical modeling approach for two-phase micro-channel heat sinks and considers also effect of surfactant on convective boiling in micro-channels.

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Evaluation of Nusselt number and pressure drop in hexagonal and rectangular micro-channels in the presence of nano-fluids

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1177/0954408920935725 ◽

2020 ◽

Vol 234 (6) ◽

pp. 665-672

Author(s):

S Emami ◽

MH Dibaei Bonab ◽

M Mohammadiun ◽

H Mohammadiun ◽

M Sadi

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Pressure Drop ◽

Cross Section ◽

Rectangular Cross Section ◽

Heat Sinks ◽

Nano Particles ◽

Geometrical Parameters ◽

Micro Channels ◽

Nano Fluids

Few papers investigated the effect of different nano-fluids and geometrical parameters of the micro channels on the performance of heat sinks. In this study, Nusselt number and pressure drop are investigated in differential geometry and Reynolds numbers. Then the effect of the micro-channel is studied for different heat flux. The results show that hexagonal micro-channels represents a better performance than the rectangular and the heat transfer of without using nano-particles in the hexagonal cross-section is about 9% higher than the rectangular cross-section and with the presence of nanoparticles (Al2O3 - CUO- TiO2, φ = 4%), heat transfer is about 30 to 40% higher than the base liquid.

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