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Physics Students A-Maze With Leidenfrost Effect

posted 29 Nov 2013, 08:24 by Mpelembe Admin   [ updated 29 Nov 2013, 08:25 ]

An aluminium maze which demonstrates the so-called 'Leidenfrost effect' in which water droplets can travel upwards on heated surfaces could help inspire a new wave of non-electric thermostats.

BATH, ENGLAND, UK (UNIVERSITY OF BATH) -  A video produced by British students showing an aluminium maze in which water droplets follow a designated path has become an internet hit. But the research team at the UK's University of Bath believe it could have a useful scientific purpose, by inspiring the development of a new generation of non-electric thermostats.

The video, produced by physics students Carmen Cheng and Matthew Guy, also shows stunning slow-motion footage of magnified water droplets appearing to walk autonomously up the incline of a jagged surface, demonstrating the 'Leidenfrost effect'.

The Leidenfrost Effect was named after German doctor and theologian Johann Gottlob Leidenfrost, who brought it to scientists' attention in 1756. It occurs when a liquid comes into contact with a mass significantly hotter than the liquid's boiling point. The liquid comes into direct contact with the surface because of a vapour barrier that keeps the two separated, as seen in household kitchens when drops of water are used to check the temperature of a fry-pan.

Project supervisor Dr Kei Takashina, a physics lecturer at the university, says there's more to the research than fun. He wants to use the team's newly acquired knowledge to build a new-style thermostat, one that could eventually lead to new, safer, cooling systems which may find applications in places such as power stations. He says such a system could help prevent a repeat of Japan's Fukushima nuclear disaster of 2011, in which a tsunami knocked out power generators used to cool the reactors.

Takashina says the Leidenfrost Maze is a useful tool for explaining how the Leidenfrost Effect works.

"If you put a droplet somewhere on the maze it will follow a pre-determined path and go round the maze, and I'll quickly show you that. So if I put droplets here you can see that the droplet goes round this loop through this zigzag path and then all the way round and it'll keep continuing to go," he said.

Takashina's team have been investigating the strange phenomenon that allows water droplets to levitate and even climb uphill. When droplets of water on a heated surface reach a certain temperature, the droplet surface starts to boil rapidly, allowing it to float or levitate on the evaporated gas vapour.

"This surface here is a hot surface and if I put water on there you can see that the water droplets make really round droplets. A film of gas is holding them above the surface, so the droplet doesn't make wetting contact with the surface and this stops the droplet from evaporating and boiling in the normal way," said Takashina.

Students Alex Grounds and Richard Still looked at how droplets travel on different textured surfaces, heated at varying temperatures. Their research, published in Nature Group journal Scientific Reports, found they could change the direction of the droplets' movement by changing the temperature of the ratcheted surface. They also found that droplets can be made to climb up a steep incline - the sharper the teeth of the surface, the steeper incline they were able to climb.

Takashina's team are attempting to widen scientific understanding of the effect, which has been known about for centuries but continues to reveal surprises. Their next project is to build a prototype thermostat.

"It's (Leidenfrost effect) potentially useful because you can use it to control heat transfer. So, for example, if the droplet moves in a different direction at a high temperature then you can use that directionality to say if the surface becomes too hot you can guide the droplet back to a cooling system, or if it's too cool you can get rid of the water, for instance. So you can have a thermostat based on this effect, for example."

Takashina says eventually such thermostats could lead to technology that would help prevent damage at future nuclear disasters. The Fukushima power-plant catastrophe was initiated by the tsunami of the Tōhoku earthquake and tsunami of March, 2011. The damage produced equipment failures, which led to a loss-of-coolant accident, and subsequent nuclear meltdowns and release of radioactive materials. It was the largest nuclear disaster since the Chernobyl disaster of 1986.

"If you remember the nuclear disaster in Fukushima what happened there was that the tsunami knocked out the power generators that run the pumps to cool the reactors. So even though the power plant makes energy and makes electricity it can't control its own temperature without electricity. And so here if you can have a system that cools the system without any extra power then this will be an advantage," said Takashina.

The team says its prototype thermostat should be ready within six months.