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This study evaluates the effect of using alumina (Al2O3)-water nanofluids stabilized by sodium dodecylbenzene sulfonate (SDBS) on the thermal performance and capillary limit of a screen mesh heat pipe. Nanofluids were prepared using three Al2O3 concentrations (0.1 mass/%, 0.5 mass/%, and 1.0 mass/%) and two SDBS concentrations (0.064 mass/% and 0.32 mass/%). The stability of the nanofluids was studied by means of UV-absorbance measurements prior to the experimental test. The results show that the thermal resistance of the heat pipe decreased by up to 50% with Al2O3 and SDBS at concentrations of 0.5 mass/% and 0.32 mass/%, respectively. Nevertheless, the capillary limit was reduced between 25 and 45 W compared to the operation with water. Finally, the capillary limit was improved by 5 W (compared to water) using an Al2O3 concentration of 0.1 mass/% and no surfactant. [ABSTRACT FROM AUTHOR]

Nanofluids have been introduced as new-generation fluids able to improve energy efficiency in heat exchangers. However, stability problems related to both agglomeration and sedimentation of nanoparticles have limited industrial-level scaling. A fractional factorial experimental 2 k−1 design was applied in order to evaluate the effects of nanoparticle concentration, surfactant type and concentration, ultrasonic amplitude as well as ultrasonic time on the stability of alumina (Al 2 O 3 ) nanofluids. Commercial alumina nanoparticles (particle diameter <50 nm) were dispersed in deionized water using ultrasonic probe dispersion equipment. Sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) were used as surfactants. The stability of the nanofluids in static mode was monitored by visual inspection and UV visible spectroscopy. The results of the experimental design showed that the coupled effects between surfactant type and surfactant concentration and between ultrasonication tip amplitude and ultrasonication time had the most pronounced effects on nanofluid stability. The experimental conditions providing the best stability were 0.5 wt% of Al 2 O 3 , CTAB, critical micelle surfactant concentration, 30% ultrasonic amplitude and 30 min of ultrasonication. [ABSTRACT FROM AUTHOR]