Scientists explain why food still clings to your stoopid non-stick pan


A ceramic granitech pan, showing a dry spot in the center - the result of thermocapillary convection.

A ceramic granitech pan, showing a dry spot in the center – the result of thermocapillary convection.
The image: Alex Fedorenko

An investigation into the way the oil behaves on hot, flat surfaces has revealed the process responsible for foods sticking to non-stick frying pans.

I love the starting line for this new Paper, Published today in Physics of Fluids: “Here, the phenomenon of food while frying in a frying pan is explained experimentally.”

Brief and straight to the point, as is the explanation: “thermocapillary convection,” according to the authors, Alexander Fedorenko and Jan Hubry, both from the Czech Academy of Science.

This is very powerful knowledge. The next time this happens while cooking, you can shake your angry fist on the stovetop and say, “Curse you, thermocapillary convection!” This will be a very satisfying moment, not only because you have a fancy new word at your disposal, but also because you will have full knowledge of what it actually means.

For their experiment, Fedorenko and Hribi, experts in fluid dynamics and thermophysics, tested two non-stick frying pans – one coated in ceramic particles and one covered with Teflon. The pans covered the surfaces of the pans with a thin layer of oil, and then, using an overhead camera, the scientists measured the speed at which the sunlight was heated as dry spots formed and grew.

Scientists noticed that, as the bottoms were heating from below, a temperature gradient began to appear across the oily film. This in turn created a surface tension gradient, which directed the oil away from the center of the pan and toward the perimeter; Liquids with high surface tension pull more forcefully onto the surrounding fluids than those with lower surface tension.

A Teflon pan showing effect in action.

A Teflon pan showing effect in action.
The image: Alex Fedorenko

This is a classic example of thermocapillary convection at work — a phenomenon in which a surface tension gradient forces a liquid (in this case, oil) to migrate outward. Once this happens, it is more appropriate to paste the food into the center of the pan, “according to the study, forming a dry spot in the thin sunflower oil film”.

Fedorenko and Herbie actually created a formula to calculate the “dewetting rate”, which measures the speed of recirculating oil droplets. Very good, but the word “dewetting” is something we don’t need in our lives right now. Scientists also identified conditions that lead to dry places, resulting in the following advice:

“To avoid unwanted dry spot formation, the following set of measures (and / or) should be applied: increasing the thickness of the oil film, medium heating, thoroughly moistening the pan’s surface with oil, a thick Using pan along the bottom, stirring food regularly during cooking, ”the author writes.

Wow! What a say. Don’t know about you, but all of this is pretty obvious advice for me (not to mention how the first and third items on that list are basically the same thing). Other than using pans with a thick bottom – I had no idea. But to be fair, I often use a cast iron pan when frying foods, so I must subconsciously let this be true.

Anyhow, all this is making me very hungry, so I’m going to end it right here, go to the kitchen, and try my best to master idiosyncris thermocapillary convection.

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