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We report a series of experiments carried out with a dichloromethane drop deposited on the surface of an aqueous solution containing a surfactant, cetyltrimethylammonium bromide. ...After an induction stage during which the drop stays axisymmetric, oscillations occur along the contact line. These oscillations are succeeded by a spectacular spontaneous spinning of the drop. The latter quickly takes the form of a two-tip ‘rotor’ and the spinning rate stabilizes at a constant value, no longer varying despite the gradual changes of the drop shape and size. The drop eventually disappears due to the continual dissolution and evaporation of dichloromethane.
Schlieren visualizations and particle image velocimetry are used to establish a consistent scenario capable of explaining the evolution of the system. The Marangoni effect induced by the dissolution of dichloromethane in the drop vicinity is shown to be responsible for the observed dynamics. Arguments borrowed from dynamical systems theory and from an existing low-order model allow us to explain qualitatively why the system selects the spinning configuration. The geometry of the immersed part of the drop is shown to play a crucial role in this selection process, as well as in the regulation of the spinning rate.
Air humidity effects on water-drop icing Sebilleau, Julien; Ablonet, Emeryk; Tordjeman, Philippe ...
Physical review. E,
09/2021, Letnik:
104, Številka:
3
Journal Article
Recenzirano
The canonical problem of the icing of a water drop lying on a cold substrate is revisited to take into account the effects of atmospheric conditions on the icing front kinetics and on the tip ...formation. Here, we demonstrate both experimentally and theoretically that the air humidity induces liquid-vapor phase change at the icing droplet interface and that the associated heat transfer has a strong influence on both the icing front kinetics and the iced drop shape. The experimental results obtained in this study, as well as results from literature, compare well to a modified Stefan model accounting for the effects of humidity, showing a good agreement with the experimental data of both the front kinetics and tip angle.
This article discusses the equilibrium states and more particularly the equilibrium thickness of large lenses of a liquid spread over the surface of a denser liquid. Both liquids are supposed to be ...nonvolatile and immiscible. Taking into account the effect of intermolecular forces in addition to the sign of the spreading parameters leads to four possible states. The three first are similar to the states of equilibrium of a liquid spread on a solid surface: total wetting where the floating liquid spreads until it reaches an equilibrium thickness on the order of the molecular size, partial wetting where the floating liquid forms a lens of macroscopic thickness in equilibrium with a “dry” bath, and pseudopartial wetting where the floating liquid spreads as a lens of macroscopic thickness in equilibrium with a thin film covering the bath. The last regime, called pseudototal wetting, consists of a macroscopic lens of the floating liquid covered with a thin film of the bath. These four regimes are described through a free-energy minimization, and their equilibrium thicknesses are predicted. A comparison of this model with experimental results available in the literature and dedicated experiments for the pseudototal wetting state are reported.
Pool boiling on flat plates in microgravity has been studied for more than 50 years. The results of recent experiments performed in sounding rocket are presented and compared to previous results. At ...low heat flux, the vertical oscillatory motion of the primary bubble is responsible for the increase in the heat transfer coefficient in microgravity compared to ground experiments. The effect of a non-condensable gas on the stabilisation of the large primary bubble on the heater is pointed out. Experiments on isolated bubbles are also performed on ground and in parabolic flight. The effect of a shear flow on the bubble detachment is highlighted. A force balance model allows determining an expression of the capillary force and of the drag force acting on the bubble.
•New data on flow boiling pipe flows in microgravity are presented: flow pattern, heat transfer coefficient.•A criteria for dependence of heat transfer coefficient on gravity is proposed.•A ...correlation for the prediction of heat transfer coefficient in microgravity is based on the model of Kim and Mudawar (2013) including heat transfer due to nucleate boiling and convection.
The development of long-term space thermal management systems has informed research into the influence of gravity on boiling. This work explored the influence of gravity on the hydrodynamics and heat transfer of boiling flow. Experiments were carried out using two test loops each consisting of a 6 mmID transparent cylindrical test section. Upward (+1g) and downward (−1g) flow boiling experiments were carried out in the laboratory while microgravity (μg) experiments were carried out during a parabolic flight campaign. The results of flow visualisation showed significant influence of gravity on the flow patterns and the influence of gravity was generally limited to mass flux, G≤400kg/m2s and/or vapor quality, x≤0.35. In all three gravity conditions, the measured heat transfer coefficient was influenced by heat flux, mass flux and/or vapor quality. For liquid Reynolds number, Relo≤2000(G≤150kg/m2s) and boiling number Bo<0.002 the measured heat transfer coefficient was highest in −1g flow and lowest in μg flow but becomes comparable at Bo>0.002. A correlation for predicting microgravity heat transfer coefficient was proposed in this work and the proposed correlation predicted 100% of the μg data in the current work within ±20%, predicted nearly 100% of the μg data of Ohta et al. (2013) within ±30% and around 85% of the μg data of Narcy (2014) within -20% to +50%. A correlation for predicting the gravity dependent regime as it relates to heat transfer coefficient in +1g and μg flows was also proposed in this work. The proposed criterium correctly predicted over 85% of the gravity-dependent heat transfer coefficient in the current work and the works of (Lebon et al., 2019; Narcy, 2014; Ohta et al., 2013).
Gravity dependence Map: Bo<0.002−0.0021+e−2(Frm−2) Prediction of heat transfer coefficient in microgravity h2∅_μg=(1.15hnb_+1g)2+(F.hcb_+1g)2 Display omitted
•Detailed experimental characterization of flow boiling in a millimetric tube in vertical upward and downward flows configurations.•Characterization of the flow patterns, void fraction, wall and ...interfacial shear stresses and wall heat transfer.•Modelling of the wall shear stress based on the contribution of both the convection and nucleate boiling.•Modelling of the interfacial shear stress, based on the characterization of the interfacial waves.
Upward and downward vapor-liquid vertical flows inside a vertical 6 mm sapphire tube was investigated using HFE-7000 as working fluid. The goal was to investigate the effect of flow direction and wall heating on two-phase parameters such as flow pattern, wall shear stress (τw), interfacial shear stress (τi) and interfacial wave structures. The mass flux, heat flux and vapor quality ranges were 50≤G≤400kg/m2.s,0≤q≤3W/cm2 and 0≤x≤0.7 respectively. Bubbly, slug, churn, annular flow patterns were observed in upward and downward flows. A falling film regime occurred in downward flow at low mass fluxes. Void fractions were higher in downward flow than in upward flow due to gravity effect, and were in good agreement with drift flux models of the literature. The wall shear stress increased with the wall heat flux due to the bubble nucleation at the wall. Following a similar approach to Kim and Mudawar (2013b), a correlation for the wall shear stress taking into account the forced convection and the bubble nucleation was derived and provided a good estimation of the experimental data within ±20%. From image processing of the high-speed visualizations, velocities (Uw) and frequencies (Fw) of the disturbance waves in annular flow were measured. The interfacial shear stress was found to directly depend of the product Uw×Fwand a prediction of the interfacial friction factor was proposed in flow boiling for both upward and downward flows.
This work entails experimental measurement and theoretical modeling of heat transfer coefficient (HTC) for annular flow boiling in upward and downward flow configurations. The working fluid used was ...HFE-7000 and experimental measurements were carried out inside a
6
mm
sapphire tube coated externally with indium-tin-oxide (ITO) for Joule heating. The range of vapor quality, mass flux, and heat flux investigated were 0.15 − 0.7, 75-400 kg/(m
2
s), and 0.5 − 3.0 W/cm
2
, respectively. Theoretical models for predicting HTC in upward and downward flows were developed using heat-flux-dependent wall shear stress correlations and roll-wave-velocity-based interfacial damping function. It was found that interfacial damping depends on the Reynolds number of the liquid film. The proposed models predicted over 96% of the measured HTC within ±20% in both upward and downward flows and reproduced the heat flux dependence of the HTC. The models also predicted over 96% of the measured liquid film thickness within ±30% in both upward and downward flows.
Experimental study of steady and transient subcooled flow boiling Scheiff, V.; Bergame, F.; Sebilleau, J. ...
International Journal of Heat and Mass Transfer/International journal of heat and mass transfer,
January 2021, 2021-01-00, 20210101, 2021-01, Letnik:
164
Journal Article
Recenzirano
Odprti dostop
•Heat transfer in subcooled nucleate flow boiling regime is investigated in steady state with set heat flux or set temperature.•Characteristic bubble sizes and velocities are determined from image ...processing and correlations for the bubble diameter et velocity are derived.•In transient nucleate boiling regime with a constant heating rate, a correlation for the prediction of the wall heat flux in transient regime versus the wall temperature is provided.
This study aims to better characterize the heat transfer and flow structure in the fully developed nucleate flow boiling regime in a semi-annular duct. Experiments with a refrigerant HFE7000 were performed in the range of Reynolds numbers from 13 000 to 40 500, subcoolings close to 15 ∘C, for constant heating power, constant wall temperature and constant heating rates (linear increase of the wall temperature).
With constant heating power, the wall heat flux is well predicted by a Chen-type correlation based on a contribution due to the forced convection and a contribution due to nucleate boiling, including the effect of the liquid subcooling. A thin layer of bubbles sliding along the wall is observed. The characteristic diameter of the bubbles increases with the heat flux and decreases with the liquid velocity and its subcooling. The bubble diameters can be well predicted versus 3 dimensionless numbers: the Reynolds number of the flow, the Jakob number based on the liquid subcooling and the Boiling number. A drag coefficient of the bubbles sliding on the wall is estimated from the measurements of the bubble relative velocities and is in good agreement with the recent numerical simulation of Shi et al. 1 for a spherical bubble moving close to a wall in a shear flow. In the experiments with a constant set temperature, a non-homogeneity of the surface temperatures is observed as well as high fluctuations of temperatures and heat fluxes. The heat transfer is strongly degraded ( ≃ 60%) by comparison with heating with a set power. Finally a transient nucleate boiling regime with a constant temperature increase dT/dt is investigated. For dT/dt < 50 ∘C.s−1, the results are similar to those of Auracher and Marquardt and a correlation for the prediction of the wall heat flux versus the wall temperature in the transient nucleate boiling regime is provided.
This publication lays the foundation for the description of the Multiscale Boiling Experiment, which was conducted within two measurement campaigns on the International Space Station between 2019 and ...2021. The experiment addresses fundamental questions about two-phase heat transfer during boiling processes. For this purpose, single or few subsequential bubbles are selectively ignited on a heated substrate using a short laser pulse. A detailed investigation of the phenomena is possible, as the boiling process is temporally slowed down and spatially enlarged in microgravity. Within the Multiscale Boiling Project, the undisturbed growth of the bubbles, the influence of a shear flow, and the influence of an electric field are investigated within the same test facility using FC-72 as working fluid. Within the project, thirteen research groups from eight countries are collaborating. Over 3000 data sets have been generated over an 11-month measurement period. In the context of this publication, besides the motivation and necessity of such investigations, the basic structure of the experiment, the objectives of the investigations, and the organization are described. Finally, first results of the investigations are presented. Therefore, this publication has the primary aim to serve as a basis for many further planned publications and present the project as a whole.
•Pool boiling research on-board the International Space station.•Effect of electric field, shear flow, and combined electric field and shear flow.•Reference publication for all upcoming results and analysis based on this project.
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