Upgrading may give existing thermal oils substantially better conductivity
Spanish researchers have developed and patented a nanofluid that offers as much as 30% better conductivity than its base heat transfer fluid while maintaining the operating temperature range of that fluid. The team in the multiphase fluid research group at Universitat Jaume I, Castelló de la Plana, achieved the enhanced performance by adding nanoparticles made of carbon and stabilizers to a conventional diphenyl/diphenyl-oxide heat transfer fluid. The nanoparticles are inexpensive. Incorporating them should incur an incremental cost of less than €1/liter (<$4.65/gallon) or under 5% of the cost of the base fluid, notes José Enrique Juliá Bolivar, a professor of fluid mechanics at the university. Moreover, nanoparticle addition can upgrade existing heat transfer systems, he says. “Almost any current heat transfer fluid with a working temperature up to 400°C can be upgraded with our method. In addition, standard pumping and piping systems can be used.”
RESEARCHERS
Figure 1. Spanish team uses nanoparticles to improve the performance of heat transfer fluids. Source: José Enrique Juliá Bolivar, Universitat Jaume I.
“One of the major problems of nanofluids is their stability, especially at high temperature. Nanoparticles move inside the base fluid and collide. If after the collision they agglomerate, the nanofluid no longer is stable and settles. We managed to get a nanofluid with high nanoparticles concentration and with negligible sedimentation for several days (even when at rest).”The nanoparticles raise the viscosity of the base fluid moderately but not enough to cause pumping problems, he notes. The specific increase depends upon the temperature range of the application but typically runs about 50%, says Juliá Bolivar.“Our methodology works with almost all synthetic organic/silicone heat transfer fluids. The best known are Therminol VP1 and Dowtherm A but there are more than thirty commercially available heat transfer fluids in which our approach can be applied.”So far, the nanofluid only has been tested at the laboratory scale. However, the researchers hope to run pilot-scale trials with the support of heat-transfer-fluid makers or other companies. An agreement may be signed by mid-2015, Juliá Bolivar believes.“Two of the strongest points of this new nanofluid are the low cost of the materials used and that its production is easily implementable. If a company licenses the technology, we hope that the new nanofluid can be on the market in less than one year.”
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