Flow boiling heat transfer characteristics using a new nanofluid, multi-walled carbon nanotubes (MWCNTs)/pure water were investigated in a horizontal tube under atmospheric pressure. In order to prepare nanofluid, gum Arabic (GA) as a surfactant and MWCNTs nanoparticles were used in the ratio 1:1 with concentrations of 0.001 and 0.01% by mass, and its stability was determined by measuring zeta potential. During the experiments, detailed observations of the boiling process showed physical differences between nuclear boiling of pure water and nanofluid especially after CHF phenomenon. These differences were mainly due to the deposition of carbon nanotube nanoparticles on the heat transfer surface and improvement in wettability and re-wetting characteristics. The experimental data showed that using nanofluid can improve the flow boiling characteristics of CHF. Based on these results, it was found that the nanofluids heat transfer coefficient was larger than that of pure water and it increased with increasing mass flux and also with increasing heat flux for both pure water and nanofluids. The enhancement of the maximum heat transfer coefficient of MWCNTs-GA/water nanofluid was approximately 4.3% at CHF and 0.005 volume fraction of nanoparticles. The results also showed that the pressure drop of nanofluid increases with increasing mass flux and the enhancement of maximum pressure drop was approximately 0.12 vol% at CHF and 0.005 vol% of nanoparticles.

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