![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
Abstract
Experiments using nanofluids in horizontal, rectangular, high-aspect-ratio microchannels were performed where heat was provided electrically to the microchannel wall to bring about heating and phase change while recording temperature (via infrared camera) and channel pressure drop. High-speed video captured images of boiling two-phase flow through the transparent microchannel wall. Nanofluids used were solutions of aluminium oxide in ethanol with particle concentrations from 0.01% to 0.1%, with pure ethanol as reference. Fluid mass flux ranged from Reynolds numbers of 2.3 to 18.1 and heat fluxes from 1.5 to 9 kW m−2. Friction factors for the nanofluids were evaluated. Single-phase fluid pressure drop did not vary significantly with nanoparticle concentration. When flow boiling occurred, the two-phase flow pressure drop was unstable and fluctuating. Inlet pressures had greater amplitude of oscillation but similar frequency to outlet pressures. Heat transfer increased with the presence of nanoparticles compared with pure ethanol. Moreover, evaporation from the meniscus was studied. There is a sudden evaporation phenomenon where the meniscus rapidly forms. Infrared data demonstrate the effect of heat flux on temperature distribution near the three-phase contact line. Nanoparticles enhance boiling heat transfer coefficients, peaking at a concentration of 0.05% with significant enhancement over pure ethanol.
NOMENCLATURE
| A | = | area |
| cp | = | specific heat capacity |
| d | = | diameter |
| f | = | friction factor |
| G | = | mass flux |
| h | = | convective heat transfer coefficient |
| K | = | loss coefficient |
| l | = | length |
| = | mass flow rate | |
| P | = | pressure |
| q | = | heat flux |
| Re | = | Reynolds number |
| T | = | temperature |
| u | = | velocity |
| W | = | width |
| z | = | distance along channel |
Greek Symbols
| θ | = | angle |
| μ | = | viscosity |
| ρ | = | density |
| σ | = | aspect ratio |
| φ | = | volume fraction |
Additional information
Notes on contributors
Gail Duursma
Gail Duursma obtained her first degree in chemical engineering from the University of Cape Town and her D.Phil. from the University of Oxford, and is currently a lecturer in chemical engineering at the University of Edinburgh.
Khellil Sefiane
Khellil Sefiane has M.Sc. and Ph.D. degrees in chemical engineering. He is presently a professor and ExxonMobil Fellow at the University of Edinburgh and is head of the Institute of Materials and Processes.
Alexandre Dehaene
Alexandre Dehaene was a student at ENSIAME, Université de Valenciennes, who did a placement at the University of Edinburgh.
Souad Harmand
Souad Harmand is a professor of engineering at ENSIAME, Université de Valenciennes, France. She is vice-president of the Université de Valenciennes and leader of the research team TEMPO.
Yuan Wang
Yuan Wang obtained her Ph.D. from the University of Edinburgh and now works at the Science and Technology on Scramjet Laboratory of the National University of Defense Technology, in Hunan, China.