Infrared thermometry study of nanofluid pool boiling phenomena

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.

Bubble activation from a hydrophobic spot at “negative” surface superheats in subcooled boiling

“…Specifically, the buildup of a porous layer of nanoparticles as a result of microlayer evaporation underneath the growing bubbles might fundamentally alter the surface adhesion tension and roughness, leading to, among other things, significant reduction of the contact angle [12]. According to Gerardi et al [13], the contact angle of the ITO (indiumetin-oxide) heater seemed to drop from around 100 to 6e16 subsequent to being boiled in water-based nanofluids of silica and diamond, respectively. The resulting nanoparticles coatings on the heater surface were found to be responsible for significantly enhanced pool boiling heat transfer thanks to the pronounced effect of capillary wicking [14,15].…”

A mathematic model considering the effect of Brownian motion for subcooled nucleate pool boiling of dilute nanofluids

“…The correlation of Eq. (17) with different contact angle (22°and 78°) was compared with Buongiorno's water-silica nanofluids experimental data [18] and the results are given in Fig. 1.…”

“…Buongiorno et al [18] conducted an experimental investigation of nucleate pool boiling under the atmospheric pressure using pure water and dilute water-silica (SiO 2 ) nanofluids, respectively. Fundamental experimental data relate to the nucleate parameters, i.e., the boiling heat transfer coefficient (HTC) and the CHF were measured and compared.…”

“…It has been proved that the heat flux partition model is capable to describe the nucleate boiling of nanofluids because of its mechanistic method [18]. However, due to absentees of specific features from pure liquids, the nucleate boiling parameters including d bW , f, n and t w in Eqs.…”

“…A new correlation for the active site density of nanofluids based on the experiment data was proposed and used in the numerical simulation which provides a means to study the relative influences of surface roughness and wet ability on the active nucleation site density for nucleate boiling of nanofluids. The classic two-fluid boiling model was modified by reformulating the new closure correlations for the nucleate boiling parameters based on experimental data [18]. Comparison of the numerical results against the experimental data demonstrated that the presented model in this research has a reasonable accuracy for the simulation of nanofluids at lower heat flux.…”