Evaporation prediction of ethanol droplet by statistical rate theory

Abstract

Evaporation is one of common natural phenomenon which happens in everywhere. The application of evaporation, such as chemical industry and printing technology, affects human life everyday. However, the evaporation still cannot be predicted in an ideal method. It is found that the classical theory is not accurate and reliable enough for evaporation rate analysis. Statistical rate theory (SRT) was introduced to solve this problem. The SRT expression derived from the number of molecules transferred from the interfacial boundary between liquid and vapor phase, energy equilibrium and thermodynamics equilibrium. The final expression of evaporation rate of ethanol droplet was derived with all measurable parameter. In this study, the collected experimental data was used for SRT expression validation. The comparison between measured value and predicted value is analysed to prove that it is agreement for ethanol droplet evaporation process with SRT expression. Two terms in SRT expression was defined as phonon term and continuum term. Phonon term is depended on liquid and vapor interfacial temperature while the continuum term is because of continuum effects and its properties. The continuum term dominated evaporation rate while the condensation rate was decided by phonon term. Evaporation parameters, which are vapor phase interfacial temperature, liquid phase interfacial temperature, vapor phase pressure and drop size radius, are numerical analysed through SRT approach. For vapor phase and liquid phase interfacial temperature, the evaporation flux is slightly decreased when the vapor phase interfacial temperature is increasing. However, the increasing liquid phase interfacial temperature leads to increasing evaporation flux. Furthermore,the evaporation is decreased when the vapor phase pressure increasing. For droplet size, the evaporation flux behaves as constant when the drop size is not in nanometre scale. Once the droplet size comes into nanometre scale, the evaporation is increasing significantly. For the future work, more data from various conditions can be analysed. More materials such as methanol, glycol and acetone can be analysed via SRT approach.