Effect of Nanoparticle Size and Concentration on Pool Boiling Heat Transfer with TiO2 Nanofluids on Laser-Textured Copper Surfaces

Abstract

The enhancement of boiling heat transfer has been extensively shown to be achievable through surface texturing or fluid property modification, yet few studies have investigated the possibility of coupling both enhancement approaches. The present work focuses on exploring the possibility of concomitant enhancement of pool boiling heat transfer by using TiO2-water nanofluid in combination with laser-textured copper surfaces. Two mass concentrations of 0.001 wt.% and 0.1 wt.% are used, along with two nanoparticle sizes of 4–8 nm and 490 nm. Nanofluids are prepared using sonification and degassed distilled water, while the boiling experiments are performed at atmospheric pressure. The results demonstrate that the heat transfer coefficient (HTC) using nanofluids is deteriorated compared to using pure water on the reference and laser-textured surface. However, the critical heat flux (CHF) is significantly improved at 0.1 wt.% nanoparticle concentration. The buildup of a highly wettable TiO2 layer on the surface is identified as the main reason for the observed performance. Multiple subsequent boiling experiments using nanofluids on the same surface exhibited a notable shift in boiling curves and their instability at higher concentrations, which is attributable to growth of the nanoparticle layer on the surface. Overall, the combination of nanofluids boiling on a laser-textured surface proved to enhance the CHF after prolonged exposure to highly concentrated nanofluid, while the HTC was universally and significantly decreased in all cases.

Pool Boiling Heat Transfer Characteristics of New and Recycled Alumina Nanofluids

“…Furthermore, NPs may deposit on the surface of the heating wire, which cannot be observed visually due to the small area of the heating wire [ 32 ]. Nevertheless, based on research conducted on the boiling of nanofluids, it became certain that NPs deposit onto the boiling surface, forming micro/nano-structures that significantly influence the boiling procedure [ 25 , 33 ].…”

“…It is to be mentioned that the user type of the heating element (plate, wire, etc.) and the modifications of the heating surfaces (under different dimensions from macroscale to nanoscale and using different materials) can change the effective heat transfer area, the density of nucleation site, wettability and other factors that affect the profile of the nucleate boiling regime [ 25 , 43 ]. Furthermore, the operating conditions of the PB (e.g., saturation pressure) and the properties of the used fluid may lead to different boiling results even for the same type of nanofluids [ 28 , 44 ].…”

“…Additionally, Mori et al [ 24 ] suggested adding a plate of honeycomb on the heating area while using TiO 2 NF in a saturated PB, and a significant enhancement of CHF was observed by maximum implementation of the new technique with NFs. In addition, TiO 2 NF has been investigated in PB by Hadži’ et al [ 25 ] and an improvement in CHT of NF at 0.1 wt.% of NPs compared to DW was reported. The study was supported with SEM images before and after the exposure of NF to boiling, and a wettable layer of TiO 2 NPs on the surface was observed and specified as a key reason for the enhanced thermal performance of the PB.…”

Aluminum Micropillar Surfaces with Hierarchical Micro- and Nanoscale Features for Enhancement of Boiling Heat Transfer Coefficient and Critical Heat Flux

“…The latter plays a major role in bubble dynamics by governing processes such as nucleation, growth, coalescence, and departure [ 30 ]. Increased surface wettability leads to a delayed CHF incipience, which can be attributed to more intense liquid rewetting, while decreased surface wettability results in promoted bubble formation due to a reduced nucleation energy barrier [ 31 , 32 , 33 ]. The synergy between increased bubble nucleation sites and enhanced liquid replenishment serves to further facilitate boiling heat transfer, a concept that has been advanced by the design of surfaces with locally mixed wettability [ 15 , 34 , 35 ].…”

Heat Transfer and Fluids Properties of Nanofluids

“…Besides enhanced thermophysical properties, nanofluids also exhibit significantly enhanced boiling heat transfer performances. An experimental study on the effect of nanoparticle size and concentration on pool boiling heat transfer with TiO 2 nanofluids on laser-textured copper surfaces was conducted by Hadžić and co-workers [ 11 ]. This study aims to explore the possibility of the concomitant enhancement of pool boiling heat transfer.…”