Measurement of the vapor layer under a dynamic Leidenfrost drop

Lee, Gi Cheol; Noh, Hyunwoo; Kwak, Hee Jin; Kim, Tong Kyun; Park, Hyun Sun; Fezzaa, Kamel; Kim, Moo Hwan

doi:10.1016/j.ijheatmasstransfer.2018.04.050

Cited by 24 publications

(17 citation statements)

References 27 publications

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“…Similar conclusions are reached by OK et al [22]. Lee et al [11] showed that under dynamic conditions the cushion forms in a very short time and is only tens of micrometers thick. According to Moon et al [19] additional conditions for such interaction are associated witch changes in liquid viscosity.…”

Section: Introductionsupporting

confidence: 81%

Peculiarities in Leidenfrost water droplet evaporation

Orzechowski

2020

Heat Mass Transfer

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The investigations involved a large water droplet deposited on the heating surface, the temperature of which was higher than the Leidenfrost point. The main element of the experimental setup was the heating cylinder with K-type shielded thermocouple located in its centre just below the surface. The measuring system was located on highly sensitive scales. The analysis of the droplet behaviour in time was conducted based on measured droplet mass changes over time and also photographic data recorded with high resolution digital camera. The energy balance equation is given for the assumption that evaporation from the droplet upper surface is small compared with the amount of heat dissipated from the bottom surface. The formula for the heat transfer coefficient depends on two slope values and an orthogonal projection of the drop onto the heating surface. The slopes are estimated based on the droplet diameter linear time dependence and mass versus the contact zone relationship. The solution provides a good representation of droplet evaporation under Leidenfrost conditions. The investigations, reported in the study, which concern water droplet at atmospheric pressure deposited on a hot surface with the temperature higher than the Leidenfrost point, indicate the following regularities: droplet orthogonal projection onto the heating surface changes linearly with the droplet mass, evaporation of the same amount of mass decreases linearly with an increase in the heating surface temperature, slope of the graph showing mass loss versus the heating surface temperature successively decreases.

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Section: Introductionsupporting

confidence: 81%

Peculiarities in Leidenfrost water droplet evaporation

Orzechowski

2020

Heat Mass Transfer

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“…To clearly visualize the L-V interface profiles in the dynamic Leidenfrost phenomenon, we utilize ultrafast x-ray imaging coupled with a drop impact setup [10,19,21,33,34]. The experiments were performed at the 32-ID undulator beamline of the Advanced Photon Source, Argonne National Laboratory, to achieve high temporal (3.7 μs/frame) and spatial (2 μm/pixel) resolutions using a bright white x-ray source (10 14 ph/s/mm 2 /0.1%bw) [10,19,21,33,34]. Figure 1(a) shows the setup of x-ray imaging conducted in this research.…”

Section: Methodsmentioning

confidence: 99%

“…This range of Weber number is appropriate to demonstrate the propagation of capillary waves in relation to the dynamic Leidenfrost phenomenon, as the dynamic Leidenfrost temperatures are reachable with our setup and the drops are not fragmented after impact. A laser triggering system was installed to sense the falling drop and to trigger the camera and the fast shutter to take the images [10,19,21,33,34]. Silicon wafers of 1 mm thickness were used as a substrate and heated by a substrate heater (SU-200-IH, Maivac).…”

Section: Methodsmentioning

confidence: 99%

Downward jetting of a dynamic Leidenfrost drop

et al. 2020

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Jetting is a universal phenomenon frequently observed in nature and industries, for instance, in rain drop impact, inkjet printing, spray cooling, fuel atomization, etc. In drop impact on a superheated surface, we observe the formation of a vapor cavity beneath the dynamic Leidenfrost drop and a consecutive downward ejection of a jet into the cavity using ultrafast x-ray phase contrast imaging. We reveal that the cavity is induced mostly by the retraction of the drop and the jetting is caused by the convergence of capillary waves along the liquid-cavity interface. We find a jetting criterion based on the viscous damping of capillary waves: [OhWe 2 ] 66 ± 10. These results can provide important insight that leads to understanding and modeling of jets in nature.

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“…As the setup had to be remotely controlled, a laser triggering system was used to sense the falling drop and to trigger the camera and the X-ray beamline shutter. The method has been successfully applied previously to drops impacting on non-heated solid substrates and onto liquid layers [61][62][63] as well as heated substrates 28,30,31 . Heating of the scintillator due to the intense radiation limits the total measurement duration to ≈ 40 ms.…”

Section: Imaging Techniquesmentioning

confidence: 99%

“…The same technique can also elucidate the time-dependent contact morphology, e.g., revealing different kinds of fingering structures 24,25 and oscillatory wetting states 25,26 , or solidification in vicinity of a cold plate 27? . Complementary to that, one can determine the height profile of the liquid/vapor contact line projected onto a 2D plane from Ultrafast X-ray phase contrast imaging [28][29][30][31] . From this, the existence of contact is not obvious due to limited spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

Drop Impact on Hot Plates: Contact times, Lift-off and the Lamella Rupture

Lee,

Harth,

Rump

et al. 2020

Preprint

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When a liquid drop impacts on a heated substrate, it can remain deposited, or violently boil in contact, or lift off with or without ever touching the surface. The latter is known as the Leidenfrost effect. The duration and area of the liquid-substrate contact is highly relevant for the heat transfer, as well as other effects such as corrosion. However, most experimental studies rely on side view imaging to determine contact times, and those are often mixed with the time until the drop lifts off from the substrate. Here, we develop and validate a reliable method of contact time determination using high-speed X-ray and Total Internal Reflection measurements. We exemplarily compare contact and lift-off times on flat silicon and sapphire substrates. We show that drops can rebound even without formation of a complete vapor layer, with a wide range of lift-off times. On sapphire, we find a local minimum of lift-off times much shorter than by capillary rebound in the comparatively low-temperature regime of transition boiling / thermal atomization. We elucidate the underlying mechanism related to spontaneous rupture of the lamella and receding of the contact area.

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Measurement of the vapor layer under a dynamic Leidenfrost drop

Cited by 24 publications

References 27 publications

Peculiarities in Leidenfrost water droplet evaporation

Peculiarities in Leidenfrost water droplet evaporation

Downward jetting of a dynamic Leidenfrost drop

Drop Impact on Hot Plates: Contact times, Lift-off and the Lamella Rupture

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