Researchers Discover Heat Transfer That Expands the Liedenfrost Effect, an 18th-Century Principle

The researchers at Virginia Tech Research University, have found properties of water that could give a new look to the 18th-century phenomenon, the Liedenfrost effect. This discovery can help in using the basic properties of water to cool industrial devices. The research was conducted by Associate Professor Jonathan Boreyko and a graduate student Mojtaba Edalatpour.

Like most matter, water also exists in three forms- solid, liquid and gas. Solid-state ice changes into a liquid state, water and liquid state change into the gaseous state when heat is applied. This shows that the behavior of water changes in the presence of heat. 

According to Professor Boreyko, the water droplets do not boil when placed on aluminum plates that are heated above 150 degrees Celsius (302 degrees Fahrenheit). He explained this phenomenon using the Liedenfrost effect. This is a physical phenomenon in which a liquid produces an insulating surface or vapor layer that prevents it from boiling rapidly when close to a surface hotter than the liquid’s boiling point. Due to this, the water droplet floats in the air instead of making physical contact with the surface. This principle is often applied liquid form of water that floats in a layer of vapor. Boreyko and his team were wondering whether the phenomenon works for ice.

“There are so many papers on liquid levitation that I wanted to ask about ice levitation,” said Boreyko. “It started as a project of curiosity. What drove our research was the question of whether we could get the three-phase Liedenfrost effect of solid, liquid and vapour.”

Daniel Cusumano, then an undergraduate student at Boreyko’s lab conducted the first research above five years ago. The ice did not float when the aluminum plate was heated above 150 degrees Celsius. He continued to increase the temperature and saw the ice’s behavior. He found that the floating threshold was 550 degrees Celsius instead of 150 degrees Celsius. 

Under that temperature, the meltwater under ice continued to boil in contact with the surface instead of exhibiting the Liedenfrost effect. To know the reason behind prolonged boiling, Edalatpour and Boreyko developed new methods for heat transfer. They found that the temperature difference in meltwater caused this effect. The meltwater layer has two layers. The bottom layer boils at a temperature of 100 degrees Celsius; while the top layer sticks to the ice at a temperature of 0 degrees Celsius. This experiment explained that the bottom surface absorbs most of the surface heat. And why does the ice take more time to rise?

“The temperature differential the ice is uniquely creating across the water layer has changed what happens in the water itself because now most of the heat from the hot plate has to go across the water to maintain that extreme differential. So only a tiny fraction of energy can be used to produce vapor anymore,” explained Boreyko.

High temperatures (550 degrees of Celsius) are important for the icy Liedenfrost effect. Boiling water optimally carries heat away from the substrate. Therefore, we can feel the heat from a container of boiling water, but not from merely hot water. This means that difficulty in floating or levitating ice is a good thing as a larger temperature window for boiling can result in better heat transfer as compared to a liquid alone.

The team continued to explore the practical applications of heat transfer. It plays a crucial role in cooling automobile engines, computer devices, etc. It requires a mechanism or substance to transfer heat or energy from a hot surface and quickly redistribute it to decrease damage to the metal parts. In nuclear power plants, ice can be used for instant cooling as an emergency measure when power fails. It is also used in metallurgy for making strong and less brittle metals. 

Further, the detailed research is published in the journal Physical Review Fluid.