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Dynamics of microdroplets over the surface of hot water.

Umeki T, Ohata M, Nakanishi H, Ichikawa M - Sci Rep (2015)

Bottom Line: Although the membranes whiffle because of the air flow of rising steam, peculiarly fast splitting events occasionally occur.They resemble cracking to open slits approximately 1 mm wide in the membranes, and leave curious patterns.We studied this phenomenon using a microscope with a high-speed video camera and found intriguing details: i) the white membranes consist of fairly monodispersed small droplets of the order of 10 μm; ii) they levitate above the water surface by 10 ~ 100 μm; iii) the splitting events are a collective disappearance of the droplets, which propagates as a wave front of the surface wave with a speed of 1 ~ 2 m/s; and iv) these events are triggered by a surface disturbance, which results from the disappearance of a single droplet.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.

ABSTRACT
When drinking a cup of coffee under the morning sunshine, you may notice white membranes of steam floating on the surface of the hot water. They stay notably close to the surface and appear to almost stick to it. Although the membranes whiffle because of the air flow of rising steam, peculiarly fast splitting events occasionally occur. They resemble cracking to open slits approximately 1 mm wide in the membranes, and leave curious patterns. We studied this phenomenon using a microscope with a high-speed video camera and found intriguing details: i) the white membranes consist of fairly monodispersed small droplets of the order of 10 μm; ii) they levitate above the water surface by 10 ~ 100 μm; iii) the splitting events are a collective disappearance of the droplets, which propagates as a wave front of the surface wave with a speed of 1 ~ 2 m/s; and iv) these events are triggered by a surface disturbance, which results from the disappearance of a single droplet.

No MeSH data available.


Cluster of droplets being swamped by surface wave front.The shaded area is the wave front region of the wave length width.
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f9: Cluster of droplets being swamped by surface wave front.The shaded area is the wave front region of the wave length width.

Mentions: In this section, the amplitude of the surface wave is estimated based on the described swamping mechanism. In the steady propagation, there should be an energy balance between the energy input from the swamped droplets and the energy dissipation in the surface wave because of the viscosity. Assuming that the surface wave is localised around the wave front region with the width and depth of the wave-length λ (Fig. 9), the energy dissipation per unit time per unit length along the wave front is estimated aswhere η is the water viscosity, τ is the wave period, and h is the height or amplitude of the wave. The energy input is estimated as the product of the number of swamped droplets and the surface energy of a droplet,where v ≡ λ/τ, n, σ, and d are the wave speed, area density of the droplets, surface tension of the water, and droplet diameter, respectively. By equating ediss and einput, we obtainIf we usewith the following viscosity and the surface tension for water,Eq. (3) is estimated asThis estimate suggests that the sufficiently large amplitude of the surface wave can be maintained by the surface energy of the swamped droplets for the observed droplet density in densely populated regions.


Dynamics of microdroplets over the surface of hot water.

Umeki T, Ohata M, Nakanishi H, Ichikawa M - Sci Rep (2015)

Cluster of droplets being swamped by surface wave front.The shaded area is the wave front region of the wave length width.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4306967&req=5

f9: Cluster of droplets being swamped by surface wave front.The shaded area is the wave front region of the wave length width.
Mentions: In this section, the amplitude of the surface wave is estimated based on the described swamping mechanism. In the steady propagation, there should be an energy balance between the energy input from the swamped droplets and the energy dissipation in the surface wave because of the viscosity. Assuming that the surface wave is localised around the wave front region with the width and depth of the wave-length λ (Fig. 9), the energy dissipation per unit time per unit length along the wave front is estimated aswhere η is the water viscosity, τ is the wave period, and h is the height or amplitude of the wave. The energy input is estimated as the product of the number of swamped droplets and the surface energy of a droplet,where v ≡ λ/τ, n, σ, and d are the wave speed, area density of the droplets, surface tension of the water, and droplet diameter, respectively. By equating ediss and einput, we obtainIf we usewith the following viscosity and the surface tension for water,Eq. (3) is estimated asThis estimate suggests that the sufficiently large amplitude of the surface wave can be maintained by the surface energy of the swamped droplets for the observed droplet density in densely populated regions.

Bottom Line: Although the membranes whiffle because of the air flow of rising steam, peculiarly fast splitting events occasionally occur.They resemble cracking to open slits approximately 1 mm wide in the membranes, and leave curious patterns.We studied this phenomenon using a microscope with a high-speed video camera and found intriguing details: i) the white membranes consist of fairly monodispersed small droplets of the order of 10 μm; ii) they levitate above the water surface by 10 ~ 100 μm; iii) the splitting events are a collective disappearance of the droplets, which propagates as a wave front of the surface wave with a speed of 1 ~ 2 m/s; and iv) these events are triggered by a surface disturbance, which results from the disappearance of a single droplet.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.

ABSTRACT
When drinking a cup of coffee under the morning sunshine, you may notice white membranes of steam floating on the surface of the hot water. They stay notably close to the surface and appear to almost stick to it. Although the membranes whiffle because of the air flow of rising steam, peculiarly fast splitting events occasionally occur. They resemble cracking to open slits approximately 1 mm wide in the membranes, and leave curious patterns. We studied this phenomenon using a microscope with a high-speed video camera and found intriguing details: i) the white membranes consist of fairly monodispersed small droplets of the order of 10 μm; ii) they levitate above the water surface by 10 ~ 100 μm; iii) the splitting events are a collective disappearance of the droplets, which propagates as a wave front of the surface wave with a speed of 1 ~ 2 m/s; and iv) these events are triggered by a surface disturbance, which results from the disappearance of a single droplet.

No MeSH data available.