Phase change heat transfer induced by plasmon heat generation in liquid micro-layer inside a micro-reactor

Abstract

This study explores the concept of utilising visible light spectrum for inducing phase change via localised surface plasmon resonance (vis-LSPR) heating in a 1 µm × 50 nm (W × H) liquid micro-layer inside a micro-reactor. Several computational physics and computational fluid dynamic models were developed, coupled, and solved to calculate the spatial–temporal electromagnetic field, surface and fluid temperatures, vapour fraction, and velocity distributions inside a micro-reactor. The micro-reactor was mediated with silver nanoparticles (AgNP) coated on titanium oxide (TiO2) substrate, to create a Schottky junction aiming at maximising vis-LSPR heating. The results of the modelling showed that the transient heat transfer is highly wavelength-dependent with the highest temperature elevation obtained at 680 nm. Phase change phenomenon was observed as the general mechanism of heat transfer that can be controlled with light wavelength. Also, the exposure time controls the intensification of the phase change and the temperature of the nanoparticles. For an exposure time of 800 µs (and wavelength of 680 nm), the highest temperature achieved is 2077 K. It was also identified that longer exposure times induce a dominant heat transfer mechanism controlled by phase change heat transfer, which is manifested as a sudden and significant increase in the temperature of the working fluid. For nanoparticle radius range from 1 to 10 nm, it was shown that increasing the particle size, the electromagnetic loss in the AgNP/TiO2 also increases almost exponentially, which in turn promoted the phase change phenomenon as well. Overall, to maximise the thermal energy release using vis-LSPR, the key operating parameters, namely the size of the nanoparticle, wavelength, and exposure time, can be tuned to achieve the required fluid temperature for the target application. Also, the phase change phenomenon was the main mechanism of heat transfer accounting for fast heat transfer from the plasmonic layer to the liquid bulk.