Simultaneous measurement of monocomponent droplet temperature/refractive index, size and evaporation rate with phase rainbow refractometry. (July 2018)

• Record Type: Journal Article
• Authors: Wu, Yingchun; Crua, Cyril; Li, Haipeng; Saengkaew, Sawitree; Mädler, Lutz; Wu, Xuecheng; Gréhan, Gérard
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 214(2018)
• Page Start: 146
• Page End: 157
• Publication Date: 2018-07
• Subjects: Phase rainbow refractometry -- Droplet evaporation rate -- Temperature -- Size change -- Refractive index; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2018.04.034
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: Phase rainbow refractometry (PRR) is developed to measure droplet temperature, size and evaporation rate. Quantitative relationship between ripple phase shift and size change is theoretical derived. Transient evaporation rate of n-nonane and n-heptane is experimentally measured and compared with models. Graphical abstract: Abstract: The accurate measurements of droplet temperature, size and evaporation rate are of great importance to characterize the heat and mass transfer during evaporation/condensation processes. The nanoscale size change of a micron-sized droplet exactly describes its transient mass transfer, but is difficult to measure because it is smaller than the resolutions of current size measurement techniques. The Phase Rainbow Refractometry (PRR) technique is developed and applied to measure droplet temperature, size and transient size changes and thereafter evaporation rate simultaneously. The measurement principle of PRR is theoretically derived, and it reveals that the phase shift of the time-resolved ripple structures linearly depends on, and can directly yield, nano-scale size changes of droplets. The PRR technique is first verified through the simulation of rainbows of droplets with changing size, and results show that PRR can precisely measure droplet refractive index, absolute size, as well as size change with absolute and relative errors within several nanometers and 0.6%, respectively, and thus PRR permits accurate measurements of transient droplet evaporation rates. The evaporations of flowing single n-nonane droplet and mono-dispersed n-heptane droplet stream are investigated by two PRR systems with a high speed linear CCD and a low speed array CCD, respectively. Their transient evaporation rates are experimentally determined and quantitatively agree well with the theoretical values predicted by classical Maxwell and Stefan–Fuchs models. With the demonstration of evaporation rate measurement of monocomponent droplet in this work, PRR is an ideal tool for measurements of transient droplet evaporation/condensation processes, and can be extended to multicomponent droplets in a wide range of industrially-relevant applications.