Why is it that despite being called a nonstick frying pan, food still gets stuck on it? Also, why does the oil sometimes suddenly retreats from the center of the pan?
Despite being called a nonstick frying pan, food still gets stuck on it causing messy and unappetizing results. Now, scientists from the Czech Academy of Science have pinpointed the physics why this happens. According to them, their findings could help to improve some industrial processes.
Their findings were published in Physics of Fluids by AIP Publishing.
Fried egg stuck on a nonstick frying pan.
Convection Could Cause the Food to Get Stuck on the Pan
According to the New Scientist, the researchers conducted an experimental investigation to determine why food gets stuck on a nonstick frying pan.
Study author Alexander Fedorechko from the Czech Academy of Sciences and his colleague used an overhead camera focused on a commercial nonstick frying pan to record what will happen when the pan is coated with 1.5 mm thick of sunflower oil.
The researchers discovered that uneven heating draws the oil towards the edges of the pan in a process known as thermocapillary convection and creates a dry spot at the center. They noticed that the center of the nonstick frying pan gets heated up faster.
The surface tension decreases in the sunflower oil as the pan is heated below, increasing the temperature. A surface tension gradient is established as the temperature at the center of the pan increases directing the oil away and toward the pan's edges.
They determined the conditions that lead to the creation of the dry spots for both stationary and flowing films. They found that this includes a decrease in the local film thickness and the size of the deformed region falling below the capillary length, EurekAlert reported.
With that said, any hole that is bigger than the critical size could quickly grow. Measuring the rate at which the dry spot was formed, the researchers said it has a velocity of 5.5 cm per second.
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How to Avoid Unwanted Dry Spots
According to Fedorchenko, their experiment showed a clear reason why the food tends to get stuck on the nonstick frying pan even though its name suggests otherwise. He added that there are things that could be done to avoid getting the food stuck on the pan while cooking.
"To avoid unwanted dry spots, the following set of measures should be applied: increasing the oil film thickness, moderate heating, completely wetting the surface of the pan with oil, using a pan with a thick bottom, or stirring food regularly during cooking," Fedorchenko said.
On the other hand, he also noted that the same mechanics work in other industries as well.
Dry spots could also occur in other situations like the thin liquid films used in fluid distillation columns or in those devices that have electronic components, according to EurekAlert.
"Dry spot formation or film rupture plays a negative role, resulting in sharp overheating of the electronic components," said Fedorchenko. "The results of this study may, therefore, have wider application."
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