Numerical Simulation of Flow Boiling in Micro Channel to Study Bubble Dynamics

2019 ◽  
Author(s):  
Uday Kumar Alugoju ◽  
Satish Kumar Dubey ◽  
Arshad Javed
Keyword(s):  
Heat Flux ◽  
Thermal Management ◽  
Heat Sink ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Clear Understanding ◽  
Microchannel Heat Sink ◽  
Micro Channel ◽  
The Impact

Abstract With the recent developments in miniaturization techniques of electronic chips, the power density of these chips has risen drastically. Available thermal management technologies like air cooled heat sink and liquid cooled heat sink are unable to keep up with the demand. However, thermal management technologies using flow boiling in microchannel heat sink can dissipate higher heat fluxes. Flow boiling technologies in micro channel heat sinks are not commercially established due to issues such as reliability, flow reversal, dry out, critical heat flux, limited knowledge of bubble dynamics, correlations, etc. In this study, performance of flow boiling in a diverging microchannel with uniform heat flux condition has been investigated. Simulations have been performed on ANSYS Fluent using Volume of Fluid (VOF). VOF is used to track the interface between different phases. The impact of angle on the bubble dynamics of the coolant and flow patterns has been studied. The simulated numerical results are compiled and presented. The results provide a clear understanding of the impact of angle on the bubble dynamics in flow boiling microchannel heat sink.

scholarly journals A Study of Critical Heat Flux During Flow Boiling in Microchannel Heat Sinks

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Heat Input ◽  
Heat Sink ◽  
Flow Boiling ◽  
Strong Dependence ◽  
Heat Fluxes ◽  
Abrupt Decrease ◽  
Parallel Microchannels

The cooling capacity of two-phase transport in microchannels is limited by the occurrence of critical heat flux (CHF). Due to the nature of the phenomenon, it is challenging to obtain reliable CHF data without causing damage to the device under test. In this work, the critical heat fluxes for flow boiling of FC-77 in a silicon thermal test die containing 60 parallel microchannels were measured at five total flow rates through the microchannels in the range of 20–80 ml/min. CHF is caused by dryout at the wall near the exit of the microchannels, which in turn is attributed to the flow reversal upstream of the microchannels. The bubbles pushed back into the inlet plenum agglomerate; the resulting flow blockage is a likely cause for the occurrence of CHF which is marked by an abrupt increase in wall temperature near the exit and an abrupt decrease in pressure drop across the microchannels. A database of 49 data points obtained from five experiments in four independent studies with water, R-113, and FC-77 as coolants was compiled and analyzed. It is found that the CHF has a strong dependence on the coolant, the flow rate, and the area upon which the heat flux definition is based. However, at a given flow rate, the critical heat input (total heat transfer rate to the coolant when CHF occurs) depends only on the coolant and has minimal dependence on the details of the microchannel heat sink (channel size, number of channels, substrate material, and base area). The critical heat input for flow boiling in multiple parallel microchannels follows a well-defined trend with the product of mass flow rate and latent heat of vaporization. A power-law correlation is proposed which offers a simple, yet accurate method for predicting the CHF. The thermodynamic exit quality at CHF is also analyzed and discussed to provide insights into the CHF phenomenon in a heat sink containing multiple parallel microchannels.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 1—Design Criteria and Heat Diffusion Constraints

1994 ◽  
Vol 116 (4) ◽  
pp. 290-297 ◽  
Author(s):  
Morris B. Bowers ◽  
Issam Mudawar
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Structural Integrity ◽  
Flow Boiling ◽  
Heated Surface ◽  
Heat Sinks ◽  
Heat Diffusion ◽  
High Heat Flux ◽  
Micro Channel ◽  
Channel Diameter

Mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with a 1-cm2 heated surface were tested for their high heat flux performance with flow boiling of R-113. Experimental results yielded CHF values in excess of 200 W cm−2 for flow rates less than 95 ml min−1 (0.025 gpm) over a range of inlet subcooling from 10 to 32°C. Heat diffusion within the heat sink was analyzed to ascertain the optimum heat sink geometry in terms of channel spacing and overall thickness. A heat sink thickness to channel diameter ratio of 1.2 provided a good compromise between minimizing overall thermal resistance and structural integrity. A ratio of channel pitch to diameter of less than two produced negligible surface temperature gradients even with a surface heat flux of 200 W cm−2. To further aid in determining channel diameter for a specific cooling application, a pressure drop model was developed, which is presented in the second part of the study.

On the Operational Parameters Effects on Two-Phase Pressure Drop Characteristics of Reentrant Copper Microchannels

2016 ◽  
Author(s):  
Daxiang Deng ◽  
Qingsong Huang ◽  
Yanlin Xie ◽  
Wei Zhou ◽  
Xiang Huang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Heat Sink ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Two Phase ◽  
Cooling Systems ◽  
Phase Pressure

Two-phase boiling in advanced microchannel heat sinks offers an efficient and attractive solution for heat dissipation of high-heat-flux devices. In this study, a type of reentrant copper microchannels was developed for heat sink cooling systems. It consisted of 14 parallel Ω-shaped reentrant copper microchannels with a hydraulic diameter of 781μm. Two-phase pressure drop characteristics were comprehensively accessed via flow boiling tests. Both deionized water and ethanol tests were conducted at inlet subcooling of 10°C and 40°C, mass fluxes of 125–300kg/m2·s, and a wide range of heat fluxes and vapor qualities. The effects of heat flux, mass flux, inlet subcoolings and coolants on the two-phase pressure drop were systematically explored. The results show that the two-phase pressure drop of reentrant copper microchannels generally increased with increasing heat fluxes and vapor qualities. The role of mass flux and inlet temperatures was dependent on the test coolant. The water tests presented smaller pressure drop than the ethanol ones. These results provide critical experimental information for the development of microchannel heat sink cooling systems, and are of considerable practical relevance.

Critical Heat Flux of R-123 in Silicon-Based Microchannels

2006 ◽  
Vol 129 (7) ◽  
pp. 844-851 ◽  
Author(s):  
Ali Koşar ◽  
Yoav Peles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heat Sink ◽  
Mass Velocity ◽  
Heat Fluxes ◽  
Microchannel Heat Sink ◽  
New Correlation ◽  
Mass Fluxes ◽  
System Pressure ◽  
Silicon Based

Critical heat flux (CHF) of R-123 in a silicon-based microchannel heat sink was investigated at exit pressures ranging from 227kPato520kPa. Critical heat flux data were obtained over effective heat fluxes ranging from 53W∕cm2to196W∕cm2 and mass fluxes from 291kg∕m2sto1118kg∕m2s. Flow images and high exit qualities suggest that dryout is the leading CHF mechanism. The effect of mass velocity, exit quality, and system pressure were also examined, and a new correlation is presented to represent the effect of these parameters.

Investigation of Cooling Performance of a Swirl Microchannel Heat Sink by Numerical Simulation

2011 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Heat Sink ◽  
High Heat ◽  
Heat Fluxes ◽  
Maximum Temperature ◽  
Microchannel Heat Sink ◽  
Irreversible Damage ◽  
Cooling Performance ◽  
Large Heat

High heat fluxes have been created by the semiconductor devices due to the high power generation and shrank size. The large heat flux causes the circuit to exceed its allowable temperature and may experience both working efficiency loss and irreversible damage due to excess in their temperatures. In this paper, a swirl microchannel heat sink is designed to dissipate the large heat flux from the devices. The numerical simulation is carried out to investigate the cooling performance. Uniform heating boundary condition is applied and single phase water is selected as coolant. The present micro heat sink applies multiple swirl microchannels positioned in a circular flat plate to enhance the heat convection by creating the secondary flow at high Reynolds numbers. Copper is selected as the material of heat sink. The channel depth and width are fixed as 0.5 mm and 0.4 mm, respectively. The heat is injected into the system from the bottom of heat sink at the heat fluxes from 10 to 60 W/cm2. Flow is supplied from the top of micro heat sink through a jet hole with a diameter of 2 mm and enters swirl microchannels at the volume flow rates varying from 47 to 188 ml/min. The cooling performances of swirl microchannel heat sinks with different curvatures and channel numbers are evaluated based on the targets of low maximum temperature, temperature gradient and pressure drop.

Flow Boiling of Ammonia in a Diamond-Made Microchannel Heat Sink for High Heat Flux Hotspots

2019 ◽  
Vol 29 (5) ◽  
pp. 1333-1344 ◽  
Author(s):  
Qi Yang ◽  
Jianyin Miao ◽  
Jingquan Zhao ◽  
Yanpei Huang ◽  
Weichun Fu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Flow Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Microchannel Heat Sink

High-Flux Thermal Management With Supercritical Fluids

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Brian M. Fronk ◽  
Alexander S. Rattner
Keyword(s):  
Heat Flux ◽  
Thermal Management ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Management Approach ◽  
High Heat Flux ◽  
Two Phase ◽  
Pump Design

A novel thermal management approach is explored, which uses supercritical carbon dioxide (sCO2) as a working fluid to manage extreme heat fluxes in electronics cooling applications. In the pseudocritical region, sCO2 has extremely high volumetric thermal capacity, which can enable operation with low pumping requirements, and without the potential for two-phase critical heat flux (CHF) and flow instabilities. A model of a representative microchannel heat sink is evaluated with single-phase liquid water and FC-72, two-phase boiling R-134a, and sCO2. For a fixed pumping power, sCO2 is found to yield lower heat-sink wall temperatures than liquid coolants. Practical engineering challenges for supercritical thermal management systems are discussed, including the limits of predictive heat transfer models, narrow operating temperature ranges, high working pressures, and pump design criteria. Based on these findings, sCO2 is a promising candidate working fluid for cooling high heat flux electronics, but additional thermal transport research and engineering are needed before practical systems can be realized.

Effects of Non-Uniform Heating on Two-Phase Flow Through Microchannels

2013 ◽  
Author(s):  
Susan N. Ritchey ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Microchannel Heat Sink ◽  
Uniform Heating ◽  
Two Phase ◽  
Local Flow

As size, weight, and performance demands drive electronics packages to become increasingly thinner and more compact, volume restrictions prevent the use of large intermediate heat spreaders to mitigate heat generation non-uniformities. Instead, these non-uniform heat flux profiles are imposed directly on the ultimate heat sink, either due to chip-scale variations or the desire to cool multiple discrete devices. A better understanding of the impacts of non-uniform heating on two-phase flow characteristics and thermal performance limits for microchannel heat sinks is needed to address these thermal packaging trends. An experimental investigation is performed to explore flow boiling phenomena in a microchannel heat sink with point hotspots, as well as non-uniform streamwise and transverse heating conditions across the entire heat sink area. The investigation is conducted using a silicon microchannel heat sink with a 5 × 5 array of individually controllable heaters attached to a 12.7 mm × 12.7 mm square base. The channels are 240 μm wide, 370 μm deep, and separated by 110 μm wide fins. The working fluid is FC-77, flowing at a mass flux of approximately 890 kg/m2s. High-speed visualizations of the flow are recorded to observe the local flow regimes. It is found that even though the substrate thickness beneath the microchannels is very small (200 μm), significant lateral conduction occurs and must be accounted for in the calculation of the local heat flux imposed. For non-uniform heat input profiles, with peak heat fluxes along the central streamwise and transverse directions, it is found that the local flow regimes, heat transfer coefficients, and wall temperatures deviate significantly from a uniformly heated case. These trends are assessed as a function of an increase in the relative magnitude of the nonuniformity between the peak and background heat fluxes.

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