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Shedding light on the surface dissipation of heat

Posted: 17 Jul 2013 ?? ?Print Version ?Bookmark and Share

Keywords:boiling heat transfer? critical heat flux? nanofluid?

A team of researchers from the Massachusetts Institute of Technology (MIT) has released the details of their study centred around the concept of boiling heat transfer. According to them, they have succeeded in systematically investigating the factors that control boiling heat transfer from a surface to a liquid. This process, they added, is crucial to the efficiency of power plants and the cooling of high-power electronics, and could pave the way for improvements in how vehicles travel through water.

The research deals with a key transition point known as the critical heat flux, or CHF, a value of heat transfer, per unit time and area, where a surface's heat-transfer characteristics suddenly change: For example, when the cooling panels of an electronics system become covered with a layer of vapor that blocks heat transfer, the resulting rise in temperature can damage or destroy the equipment. The new findings could raise the value of CHF, providing extra safety margins or operating ranges for such equipment.

The research was carried out by seven MIT researchers and published in the journal Applied Physics Letters. Co-author Jacopo Buongiorno, an associate professor of nuclear science and engineering, said it could lead to safer nuclear reactors, more efficient heat exchangers and better thermal management of high-power electronics.

Until now, there has been no agreement on the relative importance of three surface attributes that could affect the onset of CHF: roughness, wettability (the ability of water to spread across a surface) and porosity. Now, after a detailed investigation, the team has found that the presence of a porous layer on a material's surface is by far the most important factor.

While other researchers have studied these surface effects, Buongiorno explained, those earlier analyses often changed multiple surface parameters at the same time, making it difficult to identify which was most important. Buongiorno's team was able to independently vary each of the three parameters, and obtained "some surprising results."

The new work grew out of the team's earlier studies of nanofluidsnanoparticles suspended in waterfor possible use in nuclear-plant cooling systems. They found that the nanoparticles, which tended to deposit on surfaces, raised the CHF, potentially boosting safety in the plant.

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