Transient pool boiling and particulate deposition of copper oxide nano-suspensions

Many methods for enhancing nucleate pool boiling have been proposed to improve the two-phase heat transfer performance in recent years. This article offers a comprehensive comment from published literature in terms of the surface modification of reinforcing heat transfer. Two types of surface modification regarding enhancement of boiling heat transfer coefficient and critical heat flux are categorized for the first time in this paper. The first and most widespread way is artificially changing the characteristics of the surface in advance to improve boiling performance, such as structured surface and surface coating with nanoparticles, namely, the “passive” technology. Oppositely, the “active” one on boiling enhancement seems to have more potential for development and it is favored by some researchers. In brief, the transformation of geometrical shape or characteristics such as wettability spontaneously occurs during boiling, the critical heat flux would thus be delayed. The heat transfer performance, as a result, would be significantly ameliorated. This kind of “smart surface” is usually made up of specific shape memory alloy, polymers, metallic oxides, etc. The mechanisms of boiling enhancement regarding modified surfaces are also reviewed, the capillary wicking, for instance, plays vital role in it. Moreover, various surfaces are presented with emphasis on their advantages/disadvantages. Through the analysis and comparison of the two kinds of modified surfaces, this review also points out some challenges existing in the current studies concerning this topic, such as numerical study, which are worth solving or optimizing to efficiently and economically improve the boiling heat transfer in future.

Review of two types of surface modification on pool boiling enhancement: Passive and active

Convective heat transfer characteristics of nanofluids including the magnetic effect on heat transfer enhancement - a review

Latest progress on nanotechnology aided boiling heat transfer enhancement: A review

Nanofluids stability effect on a thermosyphon thermal performance

The effect of nanoparticles on a single bubble-based nucleate pool boiling phenomenon under subcooled conditions has been studied. Water (as the base fluid) and two different concentrations of water-silica nanofluids (0.005% and 0.01% V/V) have been employed as the working fluids. The boiling experiments have been conducted in a specially designed chamber, wherein an ITO-coated heater substrate has been used to induce single bubble nucleation. Measurements have been performed in a completely non-intrusive manner using one of the refractive index-based diagnostics techniques, namely, rainbow schlieren deflectometry. Thus, the thermal gradients prevailing in the boiling chamber have directly been mapped as a two-dimensional distribution of hue values that are recorded in the form of rainbow schlieren images. The schlieren-based measurements clearly revealed the plausible influence of nanoparticles on the strength of temperature gradients prevailing in the boiling chamber. As compared to the base fluid, the experiments with dilute nanofluids showed that the suspended nanoparticles tend to diffuse (homogenize) the strength of temperature gradients, both in the vicinity of the heated substrate and in the thermal boundary layer enveloping the vapor bubble. An overall reduction in the bubble volume and dynamic contact angle was seen with increasing concentrations of dilute nanofluids. In addition, the vapor bubble was found to assume a more spherical shape at higher concentrations of dilute nanofluids in comparison to its shape with water-based experiments. Clear oscillations of the vapor bubble in the subcooled pool of liquids (water and/or nanofluids) were observed, the frequency of which was found to be significantly reduced as the nanoparticle concentration was increased from 0% (water) to 0.01% (V/V). A force balance analysis has been performed to elucidate the plausible mechanisms explaining the observed trends of the oscillation frequencies of the vapor bubble.

Experiments on the effects of nanoparticles on subcooled nucleate pool boiling

Understanding the growth mechanism of single vapor bubble on a hydrophobic surface: Experiments under nucleate pool boiling regime

Performance evaluation of alumina nanofluids and nanoparticles-deposited surface on nucleate pool boiling phenomena

Performance of SiO2-water nanofluids for single bubble-based nucleate pool boiling heat transfer

Dependence of single vapor bubble dynamics and heat transfer rates on varying concentration of SiO2 nanoparticles for a range of subcooled conditions (0–9 °C) has been experimentally studied under nucleate pool boiling configuration. Non-invasive measurements have been carried out using rainbow schlieren deflectometry. Results on bubble dynamics showed that the bubble diameter and aspect ratio decrease with increasing subcooling levels as well as concentration of nanofluids. The frequency of bubble oscillations was found to increase first and then decrease with increasing subcooling levels while it decreases monotonically with increasing nanofluid concentration. Bubble departure frequency increased significantly for nanofluids, while it decreased with increasing subcooling levels. Condensation effects at the bubble interface were reflected in the form of redistribution of colors around it. Schlieren images clearly revealed a spread in the spatial extent of the thermal boundary layer region caused by the suspended nanoparticles around the vapor bubble as well as near the heated substrate. This phenomenon has been considered as one of the factors that tends to alter the condensation effects and, in turn, affects the bubble dynamics. Quantitative analysis of schlieren images revealed that the natural convective heat flux increases with increasing subcooling levels, while it decreases with increasing nanoparticle concentration. Deterioration in the natural convection phenomenon in the presence of suspended nanoparticles has been attributed to the reduced strength of thermal gradients adjacent to the heater substrate. On the other hand, evaporative heat flux was observed to decrease with increasing subcooling levels and increase with increasing concentration of nanofluids.

Prasad Kangude

Papers

Experiments on the effects of nanoparticles on subcooled nucleate pool boiling

Understanding the growth mechanism of single vapor bubble on a hydrophobic surface: Experiments under nucleate pool boiling regime

Performance evaluation of alumina nanofluids and nanoparticles-deposited surface on nucleate pool boiling phenomena

Performance of SiO2-water nanofluids for single bubble-based nucleate pool boiling heat transfer

Simultaneous mapping of single bubble dynamics and heat transfer rates for SiO2/water nanofluids under nucleate pool boiling regime