New research from MIT that identifies the key attribute in surface dissipation of heat could lead to improved power plant efficiency and better cooling of high-power electronics.
A team of MIT researchers has reportedly completed what they claim is the first systematic investigation of the factors that control boiling heat transfer from a surface to a liquid, a process that is considered crucial to the efficiency of power plants and the cooling of high-power electronics.
The research focused on the relation of material surface attributes to critical heat flux (CHF) limit, a value of heat transfer, per unit time and area, at which the efficiency of a surface’s heat-transfer ability is affected. For example, when the cooling panels of an electronics system become covered with a layer of water vapor that blocks or impedes heat transfer, the resulting rise in temperature can damage or destroy the equipment. The new findings could reportedly raise the value of CHF and lead to safer nuclear reactors, more efficient heat exchangers and better thermal management of high-power electronics, study co-author Jacopo Buongiorno, an associate professor of nuclear science and engineering, said. The research is published in the journal Applied Physics Letters.
According to Buongiorno, until now, the relative importance of three surface attributes—roughness, wettability and porosity—believed to affect the onset of CHF has been the subject of intense debate. Previous work on the subject often altered multiple surface parameters at the same time, making it difficult to clearly identify which was most important.
Now however, MIT researchers have been able to determine that the presence of a porous layer on a material’s surface is the most important factor from work initially undertaken to examine the potential use of nanofluids—nanoparticles suspended in water—in nuclear-plant cooling systems.
While conducting work on nanofluids, researchers discovered that the nanoparticles, which tended to deposit on surfaces, raised the CHF, potentially boosting safety in the power plant. Though researchers were initially unable to explain why, when Buongiorno “indicated that enhancements in CHF appear to be related to the deposition of nanoparticles onto surfaces, we got excited since we had developed methodologies for systematically depositing nanoparticles onto surfaces with nanoscale control over thickness, wettability and porosity,” co-author Michael Rubner, the TDK Professor of Polymer Materials Science and Engineering at MIT, said. “Using these methodologies, we were able to produce well-defined surface characteristics and structures that made it possible to sort out the important factors at play in the process.”
Using the new techniques to independently vary each of the three surface attributes, the team determined that the nanoparticles form a hydrophilic porous coating on the surface, accounting for the improvement.
The findings may benefit both applications requiring high CHF, such as fuel rods in nuclear power plants or liquid cooling systems in high-power electronics, and applications requiring a low CHF, such as on surface of objects moving underwater to reduce drag.
