Calculation of the ?initial? thickness of the ?microlayer? during bubble boiling

Smirnov, G. F.

doi:10.1007/bf00862021

Cited by 19 publications

(21 citation statements)

References 8 publications

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“…Following Jung & Kim (2018), the theoretical data plot was obtained by considering the growth exponent n to be 0.5 for both Reynolds numbers. The theoretical models reported by Olander & Watts (1969), Van Ouwerkerk (1971 and Smirnov (1975) overpredict the values of the initial microlayer thickness in comparison to the present experimental data. The solid line represents the prediction plot proposed by Jung & Kim (2018), which is in close agreement with the present experimental data (till the maximum microlayer thickness) for both flow rates.…”

Section: Initial Microlayer Thicknesssupporting

confidence: 53%

“…In one of the recent works, Jung & Kim (2018) modified the hydrodynamic model of Smirnov (1975) by including the effects of surface tension, the non-hemispherical shape of the vapour bubble and residual flow inside the microlayer. The modified model obtained by Jung & Kim (2018) for the estimation of initial microlayer thickness is given by…”

Section: Initial Microlayer Thicknessmentioning

confidence: 99%

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Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021

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The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

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Section: Initial Microlayer Thicknesssupporting

confidence: 53%

Section: Initial Microlayer Thicknessmentioning

confidence: 99%

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021

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“…First, we have ascertained that the simple model of Cooper & Lloyd (1969), or variations thereof, cannot describe the thickness distribution with sufficient accuracy. Conversely, the analytical solution of Smirnov (1975), modified according to the arguments presented by Jung & Kim (2018), as well as our own reasoning, captures the distribution very well over a broad range of fluid properties and Jakob numbers. We have also highlighted the effect of the mean Weber number for Scriven growth on microlayer dynamics, and argued that, for vanishingly small Jakob numbers, the microlayer can remain of negligible extent, even under conditions favourable to its formation.…”

Section: Discussionmentioning

confidence: 70%

“…A more detailed analysis of the IMT problem has been performed by Smirnov (1975), the result of which reads, in compact form,…”

Section: Initial Microlayer Thickness Sensitivity Studymentioning

confidence: 99%

Comprehensive simulations of boiling with a resolved microlayer: validation and sensitivity study

Bureš

Sato

2022

J. Fluid Mech.

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The dynamics of the microlayer beneath a growing bubble in nucleate boiling significantly impacts the heat-transfer characteristics of the process. The minute thickness of the microlayer motivates the use of direct numerical simulation (DNS) to model its behaviour if empirical models are to be avoided. In this work, we develop a computational strategy for utilising DNS to model nucleate boiling by resolving explicitly the microlayer, directly coupling, in a stable manner, the mass, momentum and energy conservation equations with the conjugate heat transfer between the solid and fluid domains. To this end, closure models for the treatment of interfacial heat transfer and the dynamic contact angle are introduced and substantiated. The computational procedure is validated against relevant experimental data recently measured at the Massachusetts Institute of Technology; it is shown that the main observed growth features and surface heat-transfer characteristics are well reproduced using our model. We go on to perform a sensitivity study of the dependence of the initial microlayer thickness distribution on the applied superheat and fluid properties. The results indicate that an equation derived from lubrication theory captures the observed trends well. Finally, a first demonstration of DNS of boiling with an explicitly resolved microlayer in three-dimensional Cartesian coordinates is presented in one of the appendices.

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“…Early analytical works (Cooper and Lloyd, 1969, Olander and Watts, 1969, Van Ouwerkerk, 1971, Smirnov, 1975, Van Stralen et al, 1975 try to derive an expression for the hydrodynamic microlayer thickness from modelling the flow in the region around the outer edge of the bubble as it expands over the wall. The analyses typically assume a perfect hemispherical shape of the bubble and focus on the pure hydrodynamics of microlayer formation neglecting any depletion by evaporation.…”

Section: 'Physically-based' Predictionsmentioning

confidence: 99%

Microlayer formation and depletion beneath growing steam bubbles

Hänsch

Walker

2019

International Journal of Multiphase Flow

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Microlayers, the few-microns-thick layers of liquid that sometimes remain beneath bubbles growing on a heated substrate, are widely observed in experiments, but theoretical understanding of their formation, behaviour and role in bubble growth is limited. In this paper we present detailed interface-tracking simulations of the formation and depletion of such microlayers. Validation of our results is presented to the degree that available measurements of such a rapid and microscopic phenomenon allow. The work extends previous mechanistic hydrodynamic-only CFD simulations of early microlayer formation up to typical bubble departure times. These calculations confirm the understanding that the bubble growth rate and the resulting bubble shape determine the presence and overall extent of microlayers underneath steam bubbles. Their thickness is strongly influenced by viscous effects and surface tension. We then present coupled, physically self-consistent CFD simulations of the formation and evaporative depletion of such microlayers. This modelling suggests strongly that the evaporation process itself constitutes a significant fraction of the small resistance to heat and mass transfer presented by the very thin liquid layer. Inclusion of representations of evaporative thermal resistance, consistent with those suggested in the literature, is seen to promote the prediction of microlayer formation. Identification of the classes of conditions under which microlayers seem likely to be formed is presented, along with an assessment of their relative contributions to bubble growth. Comparisons of the predictions with recent detailed microlayer measurements indicate good agreement.

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Calculation of the ?initial? thickness of the ?microlayer? during bubble boiling

Cited by 19 publications

References 8 publications

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

Comprehensive simulations of boiling with a resolved microlayer: validation and sensitivity study

Microlayer formation and depletion beneath growing steam bubbles

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