Full-field vapor concentration and temperature field measurement of an evaporating ethanol–water binary sessile drop by tomographic laser absorption spectroscopy

Abstract

Quantitative measurement of full-field, spatially resolved temperature and concentration field of pure water and ethanol–water binary evaporating drop is realized, in which the gas-phase and interfacial temperature and concentration are accurately captured. By studying the vapor field of evaporating drop under different heating temperatures, it is demonstrated that the method can achieve a spatial resolution below 100 μm and a time resolution of <10 s. Simultaneous gas-phase temperature and concentration field measurements reveal the occurrence of buoyancy convection in the gas phase. Through the analysis of interfacial temperature and concentration distribution, it is observed that in the process of pure water drop evaporation, both buoyancy-driven convection and thermal Marangoni convection exist, while in the ethanol–water binary drop evaporation, the solutal Marangoni flow convection and thermal Marangoni convection are coupled, and the buoyancy convection is suppressed. The interfacial temperature and gas-phase water vapor concentration can be obtained from the water vapor measurement, and combined with the activity coefficient models. The liquid-phase mole fraction of water at the interface and its distribution are also obtained, such that the liquid-phase mole fraction distribution of ethanol at the interface can be obtained, and finally, the concentration of ethanol vapor near the interface is obtained. The full-field, high-resolution measurement of evaporated drops is of substantial significance for in-depth understanding of the evaporation process. The measurement of ethanol–water binary drop evaporation provides a new research perception and method exploiting the spectral dimension, providing both quantitative and qualitative observations for the study of multi-component drop evaporation.