The interaction between a heated oil bath and water droplets commonly occurs in the kitchen. It has essential implications for cooking, fire safety, and indoor air pollution.
In a new study, scientists carefully studied bubbles that form when water droplets contact heated cooking oil. They studied the interplay between the bubble dynamics in a heated oil bath, the generated sound, and the ligament-like expulsion to the surrounding air.
For their study, scientists inserted moistened chopsticks in hot oil. They demonstrated that the type and number of bubbles formed depended on the amount of water absorbed by the chopsticks and the chopstick material.
They experimented with water droplets and batter droplets suspended on a chopstick’s tip. When the water droplet struck the hot oil, it exploded, and the batter droplet created bubbles on its surface.
Later, scientists used a small piece of paper moistened with water as a model to determine what happens when food is placed in hot oil. The amount and bubbling in this situation were dependent on both the amount of water and the temperature. When water was added to the hot oil, different vapor cavities appeared.
Following these preliminary tests, more controlled research was conducted utilizing a system that allowed water droplets to be dropped into heated oil from an overhead wire on a moveable platform. The shape of the bubbles that develop when a water droplet strikes the hot oil and the sizzling sound they create when they pop were studied using a high-speed camera and a sensitive microphone.
Tadd Truscott said, “We found three bubble events in our experiments: an explosion cavity, an elongated cavity, and an oscillating cavity.”
When a water droplet enters heated oil and experiences a microexplosion due to the abrupt temperature increase, a vapor bubble emerges that can tear the surface. A water droplet explodes in the elongated cavity without rupturing the surface.
When a droplet falls off the wire and is instantly submerged, it creates an oscillating hollow. It goes through a multistep eruption and oscillates before breaking up into many little bubbles.
According to audio inputs from the microphone, the three cavity types created various acoustic or sound properties.
Truscott said, “We can distinguish different acoustic signal characteristics for each type of cavity. Deciphering the sound signals could lead to future applications, such as acoustic sensing of aerosol generation.”
- Akihito Kiyama et al. Morphology of bubble dynamics and sound in heated oil. DOI: 10.1063/5.0088065