By adding an incredibly thin coating of alumina to a metal surface, researchers at Atlanta’s Georgia Institute of Technology have doubled the rate that heat travels from a solid surface into the solid’s contents, such as from a pot on a stove to the liquid in the pot.
Pool boiling, the most common and familiar method of heating a container's contents, is a remarkably efficient heat transfer method. The transfer of heat in this case is referred to as the heat flux. There exists, however, a critical point at which a solid surface gets too hot and pool-boiling efficiency is lost.
"Delaying the critical flux could play an important role in advancing thermal management of electronics as well as improving the efficiency of a number of energy systems," says Bo Feng, the Georgia Tech researcher leading the project.
In boiling, bubbles carry away large amounts of heat from solid surfaces, but the bubbles also act as an insulator, preventing the liquid from rewetting the surface and thereby interrupting heat transfer. The alumina coating ― only a few hundreds of atoms thick (1/1,000 the thickness of a human hair) ― has a high affinity to water and, as a result, facilitates the rapid rewetting of the solid surface.
"This is the primary reason for the enhancement of heat transfer," Feng says. An atomic layer deposition technique was used to control the thickness. By achieving such a thin coating, the additional layer of alumina did not appreciably increase thermal resistance, but it did increase the overall heat transfer.
"The potential contribution of this investigation lies in tailoring the wettability of surfaces at the nanometer scale, thereby greatly increasing the heat transfer during pool boiling," says G.P. "Bud" Peterson, director of Georgia Tech's Two-Phase Heat Transfer Lab. "This is especially promising for applications where the implementation of nanotube or nanowire arrays are possible."
Nanotube and nanowire arrays are another effective way to enhance pool boiling heat transfer. Combining the two by atomic layer deposition may increase pool-boiling efficiency even further.
The article, ″Enhancement of Critical Heat Flux in Pool Boiling Using Atomic Layer Deposition of Alumina, ″ is published in theAmerican Institute of Physics' journal Applied Physics Letters.
Learn more at http://tinyurl.com/7poycra.
Boiling Breakthrough Doubles Rate of Heat Transfer
April 11, 2012