Are you an ardent science lover? If the answer is yes, you might be interested in exploring more on the Leidenfrost effect.
The Leidenfrost effect can also be termed as film boiling that occurs when a liquid comes in contact with a solid with a temperature greater than the liquid’s boiling point. When in contact, a layer of vapor is formed between the liquid-solid interface which results in creating a barrier between the two surfaces. You can find many examples of this phenomenon in daily routine like water “dancing” around in a pan.
For further details, let’s delve further into how the Leidenfrost effect works. The process of film boiling is accredited to the famous doctor and theologian Johann Gottlob Leidenfrost (1715-1794) who had described the effect in a manuscript titled A Tract About Some Qualities of Common Water.
You can find the Leidenfrost effect in the kitchen when a droplet of water is placed on a hot frying pan. If you heat the pan to the Leidenfrost point, about 200°C, the water evaporates so rapidly that a tiny layer of vapor forms between the pan and the water droplet surface which in turn protects the water from the boiling hot pan.
The vapor causes the water droplet to “dance” around in the pan as the vapor thrusts it in diverse directions. The droplet will evaporate over a particular quantity of time, but it will take meaningfully longer than if the pan was heated to a temperature above boiling, but underneath the Leidenfrost point.
Demonstrations involved in the Leidenfrost Effect
While the phenomenon of a droplet of water dances around on a pan is an appropriate example of the Leidenfrost effect, there are also other demonstrations available on the web search results that are a little more jittery and amusing. Some of them can be sticking your hand into a container of molten lead or liquid nitrogen and also distributing water droplets through a metal maze.
If performed this experiment properly with ultimate caution, your hand will remain uninjured. If that is heated to a high temperature, the water will evaporate and transform into a layer of steam that creates a blockade between your hand and the lead and temporarily protects your hand from getting burned.
Contrarily, in the liquid nitrogen case, if your hand is the “high-temperature” object, relatively of course. The boiling point of liquid nitrogen is -195.8°C which forms an insulating vapor forms as your hand has a temperature of 37°C. But you must keep in mind that the protection is transitory, and the hand must be instantly removed from the liquids to evade damage.
When a drop of water is placed on a hot surface with edges, the droplet moves in a rectilinear direction, rather than dancing around. This method can be used to direct droplets of water through The Leidenfrost Maze.
You can’t easily predict the temperature at which the Leidenfrost effect will begin. Even if the volume of the liquid remains constantly the same, the Leidenfrost point may be different with a dependence on the properties of the surface and impurities of the liquid involved. If we estimate roughly, the Leidenfrost point for a water drop on a frying pan might be 193°C(379°F).
Do you know that this effect was also described by eminent steam boiler designer, Sir William Fairbairn involving the effect of reducing the heat transfer from the hot iron surface to water like boiler? Lower temperatures in a boiler might compel the water to evaporate quickly as a result.
Leidenfrost Point and Leidenfrost Effect
The Leidenfrost point signifies the commencement of stable film boiling. It represents the point of the boiling curve where the heat flux is minimum and the surface is covered with a vapor blanket. The heat transfer from the surface to the liquid occurs with the help of conduction and radiation through vapor.
Zuber’s equation helps to derive the minimum heat flux for a big horizontal plate. Zuber constant C is 0.09 for maximum fluids at moderate pressures.
Hence, the Leidenfrost temperature is the property of a solid-liquid pair. The Leidenfrost temperature of the solid surface is the point beyond which the liquid undergoes the Leidenfrost phenomenon.
Interested in more such interesting science facts and explanations? You can also read our blog on Tissue Transplantation.