Review of drop impact on heated walls

Liang, Gangtao; Mudawar, Issam

doi:10.1016/j.ijheatmasstransfer.2016.10.031

Cited by 422 publications

(166 citation statements)

References 218 publications

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“…We hypothesize that pellet levitation is made possible by the lift provided by rapid gas production at the base of the pellet via boiling (Raack et al 2017). This is a similar physical process to that described as the Leidenfrost effect (Cengel & Ghajar 2014;Liang & Mudawar 2017), but our case differs from the classic effect because instead of a water droplet we have a mixture of a fluid and sand and instead of a solid surface we have a granular bed.…”

Section: Sediment Transport Mechanisms By Boiling Watermentioning

confidence: 88%

“…(Wagner et al 2011) and in our case the surface temperature corresponds to sand temperature (T 0 = T s ). As the pressure inside the chamber is similar between all the experiments, the boiling regime differences depend only on the sand temperature (Cengel & Ghajar 2014;Liang & Mudawar 2017). For our nominal pressure (P 0 c. 7 mbar) and sand temperatures (T s ≥ 278 K), the liquid water introduced into the MSC is unstable and boils in all of our experiments, because T e c. 275 K (Wagner et al 2011) and therefore ΔT excess ≥ 3 K. At sand temperatures greater than 288 K (ΔT excess ≈ ≥ 13 K), water vapour production is so rapid that we observe entrainment of the sand grains and lifting of millimetre-to centimetre-sized pellets (Fig.…”

Section: Sand and Water Temperaturementioning

confidence: 98%

“…At 278 K we observe limited production of small-sized pellets while at T s = 297 K we observe greater numbers of large-sized pellets with the lifting of the pellets and sliding over the surface with reduced surface friction. The capacity for pellets to slide may be giving us insight into the different boiling regimes being experienced with changes in excess temperature (Cengel & Ghajar 2014;Giraud et al 2015;Liang & Mudawar 2017). We think that experiments at sand temperatures of 278 K (ΔT excess ≈ 3 K) are experiencing a different boiling regime, probably a nucleate boiling regime, compared with those at temperature of 297 K (ΔT excess ≈ 22 K) for which the behaviour appears to be closer to a film boiling regime with the related Leidenfrost effect (Cengel & Ghajar 2014;Liang & Mudawar 2017).…”

Section: Sediment Transport Mechanisms By Boiling Watermentioning

confidence: 99%

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Downslope sediment transport by boiling liquid water under Mars-like conditions: experiments and potential implications for Martian gullies

Herny

Conway

Raack

et al. 2018

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Gullies are widespread morphological features on Mars for which current changes have been observed. Liquid water has been one of the potential mechanisms to explain their formation and activity. However, under present-day Martian conditions, liquid water is unstable and should only be transiently present in small amounts at the surface. Yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure. Here we present the results of laboratory experiments studying the interaction between liquid water flowing over a sand bed under Mars-like atmospheric pressure (c. 9 mbar). The experiments were performed in a Mars Simulation Chamber (at the Open University, UK), in which we placed a test bed of fine sand at a 25°slope. We chose to investigate the influence of two parameters: the temperature of the water and the temperature of the sand. We performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 K. Under all experimental conditions, the water was boiling. We investigated and compared the types and timing of sediment transport events, and the shapes, characteristics and volumes of the resulting morphologies. In agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water. We found four main types of sediment transport: entrainment by overland flow; grain ejection; grain avalanches; and levitation of saturated sand pellets. Our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism. The temperature of the water played a negligible or minor role, apart from the duration of sand ejection and avalanches, which lasted longer at low water temperature. At low sand temperature the majority of the sand was transported by overland flow of the liquid water. At higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water. At the highest temperatures, sediment transport was dominated by the formation of levitating pellets, dry avalanches and ejection of the sand grains. This resulted in a transport volume about nine times greater at a sand temperature of 297 K compared with 278 K. Our heat transfer scaling shows that the boiling behaviour will be enhanced under Martian low gravity, resulting in more efficient transport of sediment by levitating sand pellets even at temperatures close to the triple point. Our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water. This implied that the amount of water required to produce morphological changes at the surface of Mars could be lower than previously estimated by assuming stable liquid water. Boiling is a critical process to be considered when assessing gully formation and modification mechanisms mobilized by liquid water. Our work could ha...

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Section: Sediment Transport Mechanisms By Boiling Watermentioning

confidence: 88%

Section: Sand and Water Temperaturementioning

confidence: 98%

Section: Sediment Transport Mechanisms By Boiling Watermentioning

confidence: 99%

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Downslope sediment transport by boiling liquid water under Mars-like conditions: experiments and potential implications for Martian gullies

Herny

Conway

Raack

et al. 2018

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“…A clear example of these limitations is the study of droplet wall/interactions. Despite being studied for more than a century by many researchers as reviewed for instance in [3][4], the complex relation between droplet dynamics and heat transfer is far to be understood. The current knowledge on droplet/wall interactions recognizes wettability as playing a fundamental role in droplet dynamics and heat transfer processes.…”

Section: Introductionmentioning

confidence: 99%

Time resolved thermographic analysis of droplet impacts onto heated surfaces under extreme wetting scenarios

Pontes

Teodori

Moita³

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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The present paper explores the use of time resolved infrared IR thermography combined with high-speed imaging to describe the liquid-surface interfacial heat transfer phenomena occurring at droplet/wall interactions. Custom made calibration and post-processing methods are proposed and discussed. The results show that the methodology proposed captures very well particular details on droplet dynamics and heat transfer, allowing to identify air bubble trapping at the impact region as well as the temperature variations at the formation of the rim. Furthermore, the calibration proposed here allowed amending some physically incorrect results that were often obtained with the IR camera's default calibration. The combined analysis of droplet dynamics (e.g. the spreading factor) with the radial temperature profiles, heat flux and cooling effectiveness computation allowed establishing qualitative and quantitative trends on the effect of various parameters on the heat transfer occurring at droplet/wall interactions. Particularly, the effect of the initial surface temperature is observed to play a minor role, as long as it is low enough to prevent the occurrence of boiling. On the other hand, extreme wetting scenarios, such as superhydrophobicity limit the heat transfer between the spreading droplet and the surface. However, the thermal analysis reveals that a major reason for this is not related to the reduced contact time of the droplet on the surface (due to rebound) or air entrapment, but is rather associated to the reduced wetted area caused by the high contact angles.

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“…), and the solid surface (temperature, roughness, thermal effusivity, etc.) [1]. Descriptions of an impact are usually made on the basis of correlations with dimensionless numbers characterizing the relative magnitude of the forces acting on the impinging droplet, i.e.…”

mentioning

confidence: 99%

Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime

Chaze¹,

Castanet²,

Caballina³

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Heat and mass transfers at the impact of a droplet onto a hot solid surface are investigated experimentally. Millimetersized water droplets impinges onto a perfectly flat sapphire surface heated at 600°C. The temperature of the liquid inside the droplet is measured using the two-color laser-induced fluorescence (2cLIF) technique. Water is seeded with a temperature-sensitive fluorescent dye, while a nanosecond pulsed laser is used for the excitation of the fluorescence. The ratio of fluorescence signal detected in two appropriate spectral bands allows to determine the liquid temperature. One advantage of this non-intrusive optical technique is that it eliminates adverse effects associated with signal variations caused by droplet shape during its impact. In parallel, the temperature of the solid surface is characterized using infrared thermography. The latter measurements are made possible by the deposition of a nanosize coating of titanium aluminium nitride (TiAlN) on the upper surface of the sapphire window. Thanks to the high frame rate of the IR camera, the time evolution of the heat flux distribution at the solid surface can be reconstructed. A comparison of IR and 2cLIF techniques enable to correlate the heating of the liquid with the cooling of the wall. This reveals that most of the heat removed from the solid surface is devoted to the heating of the liquid, the energy used for liquid vaporization being significantly lower. IntroductionMany industrial applications require a rapid cooling of surfaces from high temperatures. Among the cooling technologies, spray cooling is certainly one of the most attractive for the thermal management of high heat flux systems. Compared to jet impingement, it has the capability of cooling a relatively wider surface area with a single nozzle. It also has an unrivalled cooling efficiency, meaning that significant quantities of coolant liquid can be saved to remove the same amount of heat. These features explain why it is widely employed in many industrial applications, especially in metal production and processing industry. However, while it is applied for decades, its integration remains a complex and cumbersome process because of still incomplete knowledge of the fluid flow and heat transfer characteristics. In particular, scientific investigations focused on individual droplets are still required to understand the underlying physics behind the interactions between droplets and a hot solid surface. When a drop impacts a hot wall, different behaviours are observed. The drop can spread over the solid surface and remain attached to it due to wettability forces. It can splash and creates several smaller secondary droplets or simply rebounds. Extensive experimental investigations were carried out in the past to characterize the parameters influencing the drop behavior at the impact. Among them, some can be related to the dynamic of the impacting droplets (velocity, diameter, etc.), the physical properties of the liquid (viscosity, surface tension, etc.), and the solid su...

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Review of drop impact on heated walls

Cited by 422 publications

References 218 publications

Downslope sediment transport by boiling liquid water under Mars-like conditions: experiments and potential implications for Martian gullies

Downslope sediment transport by boiling liquid water under Mars-like conditions: experiments and potential implications for Martian gullies

Time resolved thermographic analysis of droplet impacts onto heated surfaces under extreme wetting scenarios

Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime

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