A team of researchers from the Texas Tech University and Utah State University were looking at the properties of the oil droplets that are released when cooking takes place on an open frying pan with oil and found that these oil droplets could contribute significantly to indoor air pollution.
The team presented their study titled, “Out of the frying pan: Explosive droplet dynamic,” at the 70th annual meeting of the American Physical Society’s Division of Fluid Dynamics, being held Nov. 19-21, 2017, in Denver, Colorado.
Marston Research Group, Texas Tech University - Impingement and vaporization of a 5-millimeter water droplet onto a 3-millimeter film of hot canola oil. The image to the right, shot just half a second after the water first contacts the oil, shows a plethora of droplets that are released. Some droplets are submicron and can remain airborne for more than 30 minutes.
The oil droplets that are released in air during open cooking in a frying pan are called “explosive” hot oil droplets. When they come in contact with the skin, they can lead to burns and skin damage. This is something that is well known. The contribution to indoor air pollution due to the fluid dynamics of these hot oil droplets was not clearly known till date. Jeremy Marston, an assistant professor at Texas Tech University who led this study said when a single droplet of water comes in contact with hot oil it is broken into “very large number of small oil droplets” which can dissipate in the air as they jump out of the pan.
To prove their point the group of researchers took a thin layer of oil – peanut, soybean or canola oil. They measured the temperature of the hot thin layer of this oil sample using a thermocouple. Using a high speed video camera they recorded the effect of injecting a small droplet of water on the hot oil surface. Marston explained that the result was instant and “dramatic”. There is an explosion as the water which gets trapped within the hot oil vaporizes within a fraction of a second. The oil film over this vaporized water breaks and the tiny droplets of oil go “flying” everywhere.
Cooking chicken and vegetables involves use of hot oil and introduction of substantial amounts of water. Chicken breast for example is one such food which when cooked can lead to more number of oil droplets flying all over the room. Marston said Chinese cooking methods involve adding water to hot woks and this research would be relevant for them.
The problem with these droplets is their size is below a micron and when inhaled these could be dangerous air pollutants. Marston said that they are looking at the different sizes of the released droplets and how they are spread and distributed within the room with or without adequate ventilation. Marston also spoke about the detailed imaging from the high-speed video saying that they would improve upon it by using “three-dimensional volumetric imaging and thermal imaging” which would allow them to see where these droplets are going. They would be using an ‘aerosol particle sizer’ that can measure the aerosol size with accuracy up to a nanometer to detect particle size.
Indoor air pollution kills millions worldwide Marston explained but we still do not know if cooking in a poorly ventilated kitchen using techniques that release these oil droplets could be one of the reasons behind this. Marston calls these oil droplets “kitchen-based aerosols”. He said that his team is in the process of planning larger and more extensive studies to see how much indoor air pollution can contribute to indoor air pollution and if improved ventilation could help reduce and remove these ultrafine aerosols. They are planning to test “indoor air curtains” that could be part of the ventilation systems to see if they can protect against these aerosols of oil droplets.
Reference: http://meetings.aps.org/Meeting/DFD17/Session/A12.3
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