Abstract

Non-metallic oxide nanofluids have recently attracted interest in pool boiling heat transfer (PBHT) studies. Research work on carbon and silica-based nanofluids is now being reported frequently by scholars. The majority of these research studies showed improvement in PBHT performance. The present study reports an investigation on the PBHT characteristics and performance of water-based silica nanofluids in the nucleate boiling region. Sonication-aided stable silica nanofluids with 0.0001, 0.001, 0.01, and 0.1 particle concentrations were prepared. The stability of nanofluids was detected and confirmed via visible light absorbance and zeta potential analyses. The PBHT performance of nanofluids was examined in a customized boiling pool with a flat heating surface. The boiling characteristics, pool boiling heat transfer coefficient (PBHTC), and critical heat flux (CHF) were analyzed. The effects of surface wettability, contact angle, and surface roughness on heat transfer performance were investigated. Bubble diameter and bubble departure frequency were estimated using experimental results. PBHTC and CHF of water have shown an increase due to the nanoparticle inclusion, where they have reached a maximum improvement of ≈1.33 times over that of the base fluid. The surface wettability of nanofluids was also enhanced due to a decrease in boiling surface contact angle from 74.1° to 48.5°. The roughness of the boiling surface was reduced up to 1.5 times compared to the base fluid, which was due to the nanoparticle deposition on the boiling surface. Such deposition reduces the active nucleation sites and increases the thermal resistance between the boiling surface and bulk fluid layer. The presence of the dispersed nanoparticles caused a lower bubble departure frequency by 2.17% and an increase in bubble diameter by 4.48%, which vigorously affects the pool boiling performance.

Highlights

  • Pool boiling heat transfer has emerged as a popular choice of research interest due to its variety of applications in heat transfer and energy sectors

  • In the pool boiling heat transfer process, the majority of industrial appliances are operated under the nucleate boiling region because of the high heat transfer coefficient (HTC) at low wall super heat condition

  • As for the critical heat flux (CHF), it was enhanced for all concentrations as compared to water, and a 45% improvement over the base fluid was obtained with only 0.1% volume concentration

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Summary

Introduction

Pool boiling heat transfer has emerged as a popular choice of research interest due to its variety of applications in heat transfer and energy sectors. In the pool boiling heat transfer process, the majority of industrial appliances are operated under the nucleate boiling region because of the high heat transfer coefficient (HTC) at low wall super heat condition. The CHF is regulated continuously in order to avoid any physical damage to boiling surface such as burn out or meltdown. Augmentation in pool boiling heat transfer coefficient (PBHTC) as well as the critical heat flux (CHF) enhancement will be Nanomaterials 2021, 11, 2138.

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