Experimental and Mechanism Investigation on Boiling Heat Transfer Characteristics of Alumina/Water Nanofluid on a Cylindrical Tube.

Nucleate pool boiling heat transfer experiments have been conducted to nanofluids on a horizontal cylinder tube under atmospheric pressure. The nanofluids are prepared by dispersing Al₂O₃ nanoparticles into distilled water at concentrations of 0.001, 0.01, 0.1, 1 and 2 wt.% with or without sodium, 4-dodecylbenzenesulfonate (SDBS). The experimental results showed that: nanofluids at lower concentrations (0.001 wt.% to 1 wt.%) can obviously enhance the pool boiling heat transfer performance, but signs of deterioration can be observed at higher concentration (2 wt.%). The presence of SDBS can obviously enhance the pool boiling heat transfer performance, and with the presence of SDBS, a maximum enhancement ratio of BHTC of 69.88%, and a maximum decrease ratio of super heat of 41.12% can be found in Group NS5 and NS4, respectively. The tube diameter and wall thickness of heating surface are the influential factors for boiling heat transfer coefficient. Besides, we find that Rohsenow formula failed to predict the characteristics of nanofluids. The mechanism study shows that: the decrease of surface tension, which leads to the decrease of bubble departure diameter, and the presence of agglomerates in nanofluids are the reasons for the enhanced pool boiling heat transfer performance. At higher concentration, particle deposition will lead to the decrease of distribution density of the vaporization core, and as a result of that, the boiling heat transfer performance will deteriorate. Nucleate pool boiling heat transfer experiments were conducted with Al₂O₃/water nanofluids which were prepared by two-step method. The nanoparticle concentration and the presence of sodium, 4-dodecylbenzenesulfonate (SDBS), as well as the tube diameter and wall thickness of main heater were found to be the influential factors on the heat transfer performance. The investigation on the bubbles generated on heating surface, the agglomerates and the boiling surface also confirmed the heat transfer mechanism which was found in the experiments. [ABSTRACT FROM AUTHOR]