Numerical analysis of slug flow boiling in square microchannels

Ferrari, Andrea; Magnini, Mirco; Thome, John R.

doi:10.1016/j.ijheatmasstransfer.2018.03.012

Cited by 84 publications

(37 citation statements)

References 45 publications

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“…Similar results of the bubble nucleation frequency with small dependence on the wall superheat in pool boiling was presented in Hutter et al 24 A small effect of the heat flux on the nucleation frequency during vertical subcooled flow boiling was encountered by Chu et al 25 The employment of numerical analysis to flow boiling in microchannels is being studied by various research groups, however a fully functional numerical model is still far from being reached due to the complexity of the boiling phenomena. Numerical modelling of pressures, temperatures and velocities is commonly associated with twophase non-boiling flows Cioncolini and Thome, 26 specific flow patterns in predominantly larger circular microchannels Magnini and Thome, 27 single bubble growth and bubble merger in larger square microchannels Mukherjee et al 28 and Ling et el., 29 single bubble analysis Ferrari et al, 30 and is therefore not entirely relatable to the solely annular flow observed during boiling in our experimental work.…”

Section: Introductionmentioning

confidence: 56%

Oscillations During Flow Boiling in Single Microchannels

Sitar¹,

Lebar²,

Crivellari³

et al. 2018

ACSi

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Flow boiling of degassed double-distilled water in a single 50 × 50 μm and 100 × 50 μm microchannel was investigated on the basis of experimental measurements and high-speed visualization. The visualized events during boiling were analyzed in terms of the bubble frequencies and boiling front oscillations in microchannels. A digital image sequence analysis algorithm was composed to determine the time dependence of bubble and meniscus locations. The results show (i) the dynamic characteristics of boiling in microchannels, (ii) the increase of fundamental oscillation frequencies with increasing heat flux and temperature of the microchannel bottom, (iii) the amplitudes of the flow boiling oscillations are inversely proportional to the fundamental frequencies. The outcomes of the study are important as the oscillations during boiling in single microchannels are experimentally confirmed to be predictable in terms of oscillation frequencies and amplitudes trends and dependencies. This knowledge is especially significant at constructing efficient two-phase micro heat exchangers, micro mixers or micro reactors, as the cross section and the length of the channel become exceedingly important design parameters in micro devices with boiling.

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Section: Introductionmentioning

confidence: 56%

Oscillations During Flow Boiling in Single Microchannels

Sitar¹,

Lebar²,

Crivellari³

et al. 2018

ACSi

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show abstract

“…With a different approach, the rate of mass transfer is evaluated using an approximation of the net interphase mass flux derived from basic kinetic theory ('kinetic model'). Various implementations of the method have been proposed [45][46][47] based on the original interface capturing method of Hardt and Wondra [48]. The 'kinetic' and 'conduction' models are the most popular approaches for realistic simulation of boiling and have been used in various combinations with different approaches for capturing interface behaviour.…”

Section: Modelling Mass Transfermentioning

confidence: 99%

Modelling of Boiling Flows for Nuclear Thermal Hydraulics Applications—A Brief Review

Giustini

2020

Inventions

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The boiling process is utterly fundamental to the design and safety of water-cooled fission reactors. Both boiling water reactors and pressurised water reactors use boiling under high-pressure subcooled liquid flow conditions to achieve high surface heat fluxes required for their operation. Liquid water is an excellent coolant, which is why water-cooled reactors can have such small sizes and high-power densities, yet also have relatively low component temperatures. Steam is in contrast a very poor coolant. A good understanding of how liquid water coolant turns into steam is correspondingly vital. This need is particularly pressing because heat transfer by water when it is only partially steam (‘nucleate boiling’ regime) is particularly effective, providing a great incentive to operate a plant in this regime. Computational modelling of boiling, using computational fluid dynamics (CFD) simulation at the ‘component scale’ typical of nuclear subchannel analysis and at the scale of the single bubbles, is a core activity of current nuclear thermal hydraulics research. This paper gives an overview of recent literature on computational modelling of boiling. The knowledge and capabilities embodied in the surveyed literature entail theoretical, experimental and modelling work, and enabled the scientific community to improve its current understanding of the fundamental heat transfer phenomena in boiling fluids and to develop more accurate tools for the prediction of two-phase cooling in nuclear systems. Data and insights gathered on the fundamental heat transfer processes associated with the behaviour of single bubbles enabled us to develop and apply more capable modelling tools for engineering simulation and to obtain reliable estimates of the heat transfer rates associated with the growth and departure of steam bubbles from heated surfaces. While results so far are promising, much work is still needed in terms of development of fundamental understanding of the physical processes and application of improved modelling capabilities to industrially relevant flows.

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“…Their results show that the Nu ave rises happened by Re and nanoparticle volumetric percentage growth. Ferrari et al [31] conducted a numerical study on the effect of boiling inside a two-dimensional microchannel with a square cross-section. They found that for all Res, the bubble velocity in the channel with the square cross-section is higher than the other ones.…”

Section: Introductionmentioning

confidence: 99%

“…From the studies reviewed on microchannels [22][23][24][25][26][27][28][29][30][31][32][33], it can be concluded that the use of microchannels, due to the increasing need of different industries for small and efficient heat exchangers, is considered to be more than before. Therefore, the behavior of microchannels in different environments needs to be given more attention.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel

2020

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Microchannels are widely used in electrical and medical industries to improve the heat transfer of the cooling devices. In this paper, the fluid flow and heat transfer of water–Al2O3 nanofluids (NF) were numerically investigated considering the nanoparticle shape and different cross-sections of a porous microchannel. Spherical, cubic, and cylindrical shapes of the nanoparticle as well as circular, square, and triangular cross-sections of the microchannel were considered in the simulation. The finite volume method and the SIMPLE algorithm have been employed to solve the conservation equations numerically, and the k-ε turbulence model has been used to simulate the turbulence fluid flow. The models were simulated at Reynolds number ranging from 3000 to 9000, the nanoparticle volume fraction ranging from 1 to 3, and a porosity coefficient of 0.7. The results indicate that the average Nusselt number (Nuave) increases and the friction coefficient decreases with an increment in the Re for all cases. In addition, the rate of heat transfer in microchannels with triangular and circular cross-sections is reduced with growing Re values and concentration. The spherical nanoparticle leads to maximum heat transfer in the circular and triangular cross-sections. The heat transfer growth for these two cases are about 102.5% and 162.7%, respectively, which were obtained at a Reynolds number and concentration of 9000 and 3%, respectively. However, in the square cross-section, the maximum heat transfer increment was obtained using cylindrical nanoparticles, and it is equal to 80.2%.

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Numerical analysis of slug flow boiling in square microchannels

Cited by 84 publications

References 45 publications

Oscillations During Flow Boiling in Single Microchannels

Oscillations During Flow Boiling in Single Microchannels

Modelling of Boiling Flows for Nuclear Thermal Hydraulics Applications—A Brief Review

The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel

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