Effects of nanoparticle behaviors and interfacial characteristics on subcooled nucleate pool boiling over microwire

• Swirling and flocculent nanoparticle clustering phenomena near the three-phase contact line of bubble were observed.
• n-Butanol promotes the flocculent clustering process of nanofluid at low heat flux conditions.
• The heat transfer enhancement could be observed around a critical surfactant concentration.
• n-Butanol will enhance the CHF and the improvement is relatively high for high nanoparticle concentrations.
• The effect of surfactant on convection heat transfer is greater than nanoparticle deposition formed by nanofluid boiling.

The flow and heat transfer characteristics of nanofluid were attracting many researchers during the last two decades. Convection heat transfer in it is especially important for its potential applications. Therefore, it is crucial to study the nanoparticle behaviors near the near wall region and the interfacial property, which are dominant in nanofluid convection heat transfer. In this investigation, stable nanofluid was prepared with alumina nanoparticles (30 nm in diameter) and deionized water. The nanoparticle behaviors near the liquid wedge of bubbles were observed by high-speed CCD camera. The effects of nanoparticle behaviors in this region and the interfacial characteristics at the liquid–vapor interface on convection of nanofluid were experimentally investigated. Flocculent nanoparticle clustering was observed swirling near the liquid wedge, when the heat flux is relatively small. The microscopic morphology of the nanoparticle deposition layer at the heated surface was characterized by SEM images. It seems that the deposition layers could modify the morphology, but it also delays the detachment of small bubbles from the heated surface. While n-butanol was included as surfactant which will change the liquid/vapor interfacial property, it intensifies the nanoparticle deposition for low heat flux conditions. The analysis shows that the critical heat flux of nanofluid can be obviously improved when n-butanol was included in the nanofluid. It also shows that the inhibited bubble growth and enhanced nanoparticle clustering in the liquid wedge region are the main reason for the heat transfer deterioration when increasing the amount of surfactant in nanofluid. A comparative experiment indicates that the effect of surfactant on convection heat transfer is greater than the unstable deposition formed by nanoparticles.