Plunging something hot into a cold liquid is the universal cool-down method — whether putting out a campfire or cooling a nuclear reactor. A new study has offered scientists a closer look at the thermodynamics behind the method.
Using laser pulses, scientists at the University of Bristol were able to image the ultra-fast movement of energy away from a hot molecule dropped into a vat of water.
“In our experiments, small dissolved molecules were given a very large amount of energy using a short burst of ultraviolet light,” Andrew Orr-Ewing, a professor of chemistry at Bristol, said in a news release. “The energized molecules initially spin very fast and move with high speeds, but rapidly encounter molecules of the surrounding solvent.”
The collisions between the cold and hot molecules are extremely fast, lasting less than a trillionth of a second — too fast for most imaging technologies.
As the laser pulses revealed, the energy of the excited molecules dissipates as they continue to collide with their cooler neighbors. Researchers liken the process to a top spun across a table littered with obstacles.
“They ricochet off the solvent molecules and transfer energy in the process, so that they spin more and more slowly until they run out of excess energy,” Orr-Ewing said.
Scientists detailed their investigation of the cooling process in the journal Nature Chemistry.
Filed Under: Materials • advanced