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A boiling heat transfer system is used in a variety of industrial processes and applications, such as refrigeration, power generation, heat exchangers, cooling of high-power electronics components, and cooling of nuclear reactors. The critical heat flux (CHF) is the thermal limit during a boiling heat transfer phase change; at the CHF point, the heat transfer is maximized, followed by a drastic degradation beyond the CHF point. Therefore, Enhancement of CHF is essential for economy and safety of heat transfer system. In this study, the CHF and heat transfer coefficient under the pool-boiling state were tested using multi-wall carbon nanotubes (MWCNTs) CM-95 and CM-100. These two types of multi-wall carbon nanotubes have different sizes but the same thermal conductivity. The results showed that the highest CHF increased for both MWCNTs CM-95 and CM-100 at the volume fraction of 0.001%, and that the CHF-increase ratio for MWCNT CM-100 nanofluid with long particles was higher than that for MWCNT CM-95 nanofluid with short particles. Also, at the volume fraction of 0.001%, the MWCNT CM-100 nanofluid indicated a 5.5% higher CHF-increase ratio as well as an approximately 23.87% higher heat-transfer coefficient increase ratio compared with the MWCNT CM-95 nanofluid.

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