WASHINGTON, Feb. 2, 2021 – Despite using nonstick frying pans, foods sometimes go to a heating surface, even if oil is used. The results can be very deceptive and unattractive.
Scientists at the Czech Academy of Sciences began studying the mobile properties of oil on a flat surface, such as a frying pan. Their work, reported in Physics of wetness, by AIP Publishing, shows that convection is probably to blame for our hard food.
The experimental study used a non-striped pan with a surface made up of ceramic grains. A video camera was placed above the pan as it was heated and used to measure at what speed a dry spot was forming and growing. Further experiments with a Teflon-coated pan showed the same.
“We experimentally explained why food sticks to the center of the frying pan,” said author Alexander Fedorchenko. “This is caused by the formation of a dry spot in the thin sunflower oil film due to thermocapillary convection.”
When the pan is heated from below, a temperature gradient is established in the oil film. For common lifts, such as sunflower oil used in the experiment, the surface tension decreases as the temperature rises. A surface tension gradient is established, directed away from the center where the temperature is highest and toward the edge of the pan.
This gradient establishes a type of communication called thermocapillary convection, which moves oil out. When the oil film in the middle becomes thinner than the essential value, the film breaks.
The researchers determined the conditions leading to dry areas for both stationery and streaming films. These conditions include a decrease in local film thickness below critical size as well as the size of the deformed region falling below a number known as capillary length.
“To avoid unwanted dry spots, the following set of measures should be applied: increase the thickness of the oil film, moderate heating, wet the pan surface completely with oil, using a thick-bottomed pan, or moving food regularly at cooking time, “Fedorchenko said.
The phenomenon also occurs in other conditions, such as the thin-melt films used in liquid distillation columns or other devices in which electronic components may be present.
“The formation of a dry spot or film turbulence plays a negative role, leading to excessive hard heating of the electronic parts,” Fedorchenko said. “So the results of this study may be broader.”
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The article “On the formation of dry spots in melting films” is written by Alexander Fedorchenko and Jan Hruby. The article will appear in Physics of wetness on February 2, 2021 (DOI: 10.1063 / 5.0035547). After that date, it can be accessed at https: /
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