Claudiu Stan of Rutgers University in Newark, New Jersey, and his team detected an unexpected phenomenon when watching drops of supercooled water that freeze unexpectedly: the drops suddenly continued to disperse. At first, they believed that falling liquids broke when freezing. However, upon closer inspection, they discovered that cold drops were still present; they just disappeared. A quantitative model for this behavior was created by the researchers, which explains that it is caused by a rocket-like propulsion mechanism created by the freezing process. Stan claims that this discovery could motivate researchers to develop autonomous systems that move through similar phase transitions.
Contribution of Conservation of Momentum to Propulsion Systems
The team's findings add to research on self-propelled drops. While the mechanics underlying such movements are incredibly diverse, Stan observes that they always involve violations of symmetry. This symmetry violation occurs for freezing drops when ice nucleation begins off-centre. If the nucleation is off-centre, the increased evaporation will spread unevenly to the surface of the drop because when the ice nucleates, the change in structure releases latent heat, causing the local evaporation rate to suddenly increase. This asymmetrical evaporation increases the drop's momentum, and the team's model predicts top velocities of almost 1 m/s, much like a rocket launching a propellant heated by a chemical reaction.
According to Stan, this propulsion mechanism has a special quality that makes it attractive for applications: unlike most self-propelled particles, it does not need surfaces or a fluid medium (experiments were done under vacuum). However, there is an additional benefit to the exploration itself: "I'm a space travel fan, so it was fascinating to see that we were able to draw a comparison between these little drops and rockets," he adds.
Source: physics.aps.org/articles/v16/s18
Günceleme: 04/02/2023 15:37
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