What Causes Water Droplets to Oscillate Under the Leidenfrost Effect?

[Tamerlane]

First of all, let me say that I'm a french [in the way that i speak french] student and most probably my sentences will not be as accurate as they should, excuse me in advance.

To make a long story short, the Leidenfrost effect makes a water drop to stop "boiling" at temperatures higher than 240 Celsius. The principle is as follows: the suddent heating of the water (when it falls on the surface) immediately creates a vapor layer between the liquified water and the surface.

Note: we have roughly measured the actual temperature of the water at around 80 celsius.

The same effect happens with a particular plastic surface that as been "polished" (or scratched) with an extremely thin sandpaper OR a surface covered with teflon => there is small "bubbles" of air that gets trapped between the real surface and the water.

Anyway, what interests me and my group is that when you heat the water ; our optimal temperature (for the oscillating mode we concentrated on) is about 410 celsius, at that point and from a very particular volume of water [the drop constantly evaporate], it starts oscillating at a frequency of about 10Hz and increasing. At that point, the drop has a rounded triangular shape, but it's so fast, you see 6 and arguably 8 tip to the "star" it forms.

Now, i'd like to know if anybody has ever heard of or work on such thing, we'd especially like to know what exactly happens, what makes the water turn on itself or oscillate [we're not even sure about the movement of the molecules within the drop]. If there is any formula that exists to describe such phenomenon or anything else.

Also, we are being told it has something to do with surface tension, anyone can help?

Thank you

Note to anyone who might wonder: I've put this message on 2 boards

 

[member 553083]

, this one and Physics Stack Exchange, so if you find the same message in both places, it's because it's the same person.

 

[M98Ranger]

and i didn't get any answer

The Leidenfrost effect is a fascinating phenomenon that has been studied for centuries. It was first observed by Johann Gottlob Leidenfrost in 1756 and has since been studied and explained by scientists from various fields.

The basic principle of the Leidenfrost effect is that when a liquid, such as water, comes into contact with a surface that is significantly hotter than its boiling point, it does not immediately boil. Instead, a thin layer of vapor is created between the liquid and the surface, which insulates the liquid and prevents it from boiling. This creates a characteristic dancing or bouncing effect, as the liquid moves around on the vapor layer.

As you mentioned, this effect can also occur on surfaces that are not significantly hotter, but have a low surface tension or are coated with a substance like teflon. This is because these surfaces also create a vapor layer that insulates the liquid.

Now, to address your specific questions about the oscillating effect that you observed at a temperature of 410 celsius. This is likely due to a combination of factors, including the specific properties of the surface, the volume of water, and the temperature. The exact mechanism behind this oscillation is not fully understood, but it has been theorized that it is caused by the vapor layer collapsing and reforming rapidly, creating a pulsating effect on the water drop.

As for the role of surface tension, it is a key factor in the Leidenfrost effect. Surface tension is the force that holds the molecules of a liquid together and determines its shape and behavior. In the case of the Leidenfrost effect, the vapor layer created by the high temperature of the surface reduces the contact between the liquid and the surface, thereby reducing the surface tension and allowing the liquid to move more freely.

There have been numerous studies and experiments conducted on the Leidenfrost effect, but it is still a complex and ongoing area of research. There is no single formula that can fully describe this phenomenon, as it depends on various factors such as temperature, surface properties, and liquid volume.

I hope this helps to clarify some of your questions about the Leidenfrost effect. It is a fascinating topic and I encourage you to continue exploring and learning more about it.