Of interest is the accurate measurement of the enhanced thermal conductivity of certain nanofluids free from the impact of natural convection. Owing to its simplicity, wide range of applicability and short response time, the transient hot-wire method (THWM) is frequently used to measure the thermal conductivity of fluids. In order to gain a sufficiently high accuracy, special care should be taken to assure that each measurement is not affected by initial heat supply delay, natural convection, and signal noise. In this study, it was found that there is a temperature limit when using THWM due to the incipience of natural convection. The results imply that the temperature-dependence of the thermal conductivity enhancement observed by other researchers might be misleading when ignoring the impact of natural convection; hence, it could not be used as supporting evidence of the effectiveness of micromixing due to Brownian motion. Thus, it is recommended that researchers report how they keep the impact of the natural convection negligible and check the integrity of their measurements in the future researches.
Critical Invalidation of Temperature Dependence of Nanofluid Thermal Conductivity Enhancement
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 15, 2012; final manuscript received January 18, 2013; published online April 11, 2013. Assoc. Editor: Oronzio Manca.
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Han, K., Lee, W., Kleinstreuer, C., and Koo, J. (April 11, 2013). "Critical Invalidation of Temperature Dependence of Nanofluid Thermal Conductivity Enhancement." ASME. J. Heat Transfer. May 2013; 135(5): 051601. https://doi.org/10.1115/1.4023544
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