What is it about?
Have you ever wondered what happens when a droplet is heated to extreme temperatures? This scenario is relevant for many processes like burning fuels and can lead to explosive events, but as you might imagine, investigating what is going on inside of a soon-to-explode droplet is challenging. To do this anyway, we have developed a computer simulation approach based on the method of molecular dynamics, in which the movement of a large number of molecules is tracked over time. In the computer simulation, it is very easy to take a look into the droplet and observe what is going on there - see the animation at the bottom of this page. Here's how it works: We simulate a tiny droplet surrounded by vapor and then crank up the heat in the center of the droplet. Depending on the temperature in the droplet interior, different phenomena occur. At low temperatures, the droplet simply evaporates. At intermediate temperatures, a bubble forms inside of the droplet, punctures a hole into it, and the droplet eventually falls apart. For high temperatures, the droplet explodes almost instantly. What we did not anticipate: the vapor bubble inside of the droplet usually wobbles in size until it is large enough to shred the droplet into pieces, and for a very specific temperature, the droplet transformed into a donut shape! For more of our methodology and fascinating animations of droplets exploding in hot atmospheres, see a video abstract of our paper on YouTube: https://youtu.be/g8c2T3TR_AI
Featured Image
Photo by Thomas Park on Unsplash
Why is it important?
Droplet heating, evaporation, and explosions are important in many industrial processes, the classic example being the internal combustion engine. However, there are many more applications where the droplet behavior is key, such as in spray flame synthesis, a process for producing functional nanomaterials. These nanomaterials can e.g. be used in gas sensors or as cathode materials for batteries. In spray flame synthesis, high quality nanoparticles are usually only obtained if a cascade of droplet microexplosions occurs during the process. Understanding droplet explosions on a fundamental level can help us improve these processes where tiny droplets play a big role.
Perspectives
My everyday research in spray flame synthesis focuses on the droplet evaporation prior to the explosion. In my PhD project, I measure thermophysical properties of liquid mixtures and develop a mathematical model for the evaporation process. The goal is to identify under which circumstances the criteria for superheating in the droplet interior are met. However, this approach never allows me to actually observe an explosion – so it was great to contribute to this molecular simulation study, where the investigation starts where I usually have to stop!
Babette Kunstmann
RPTU Kaiserslautern
Read the Original
This page is a summary of: Explosions of nanodroplets studied with molecular dynamics simulations, Physics of Fluids, March 2024, American Institute of Physics,
DOI: 10.1063/5.0190455.
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