Abstract
Infrared thermometry was used to obtain first-of-a-kind, time- and space-resolved data for pool boiling phenomena in water-based nanofluids with diamond and silica nanoparticles at low concentration (<0.1 vol.%). In addition to macroscopic parameters like the average heat transfer coefficient and critical heat flux [CHF] value, more fundamental parameters such as the bubble departure diameter and frequency, growth and wait times, and nucleation site density [NSD] were directly measured for a thin, resistively heated, indium-tin-oxide surface deposited onto a sapphire substrate. Consistent with other nanofluid studies, the nanoparticles caused deterioration in the nucleate boiling heat transfer (by as much as 50%) and an increase in the CHF (by as much as 100%). The bubble departure frequency and NSD were found to be lower in nanofluids compared with water for the same wall superheat. Furthermore, it was found that a porous layer of nanoparticles built up on the heater surface during nucleate boiling, which improved surface wettability compared with the water-boiled surfaces. Using the prevalent nucleate boiling models, it was possible to correlate this improved surface wettability to the experimentally observed reductions in the bubble departure frequency, NSD, and ultimately to the deterioration in the nucleate boiling heat transfer and the CHF enhancement.
Highlights
Numerous studies have recently been produced on the heat transfer properties of common fluids whose properties have been modified through the addition of solid nanoparticles
We report and compare directly measured data for bubble departure diameter and frequency, growth and wait times, and nucleation site density for pure water and two water-based nanofluids, obtained using a state-of-the-art facility based on infrared thermometry [22,23]
Experimental results The nucleate boiling and critical heat flux characteristics of deionized water and water-based nanofluids were studied with infrared thermometry
Summary
Numerous studies have recently been produced on the heat transfer properties of common fluids whose properties have been modified through the addition of solid nanoparticles. Data interpretation As presented above, the nucleate boiling heat transfer coefficient and critical heat flux were found to decrease and increase, respectively, in nanofluids These behaviors are compatible and related to the surface modification that was observed due to the porous nanoparticle layer deposited via boiling. Nucleate boiling heat transfer coefficient deterioration in nanofluids Influence of thermal resistance of nanoparticle surface deposit on boiling curves The infrared camera measures temperatures on the backside of the ITO heating element. The change in contact angle can explain a significant portion of the deterioration of heat transfer coefficient in nanofluids Note that this analysis is very approximate since the maximum superheats for the highly wetting nanofluid surfaces are under 50°C, while the prediction for homogenous nucleation of water at atmospheric pressure is approximately 220°C. Kim and Kim [21] explored the effect of porous nanoparticle layers on CHF due to capillary wicking and showed that a portion of the CHF increase could be explained by capillary wicking
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