Evaluation of Evaporation Models for Single Moving Droplet with a High Evaporation Rate

Evaporation of a moving liquid droplet in atmosphere is a common phenomenon with wide engineering applications. Theoretical models that consider mass, momentum, and energy transfer between the droplet and the surrounding gas have been well documented in the literature to predict the variation of the velocity, the size, and the temperature of a moving droplet. Carefully designed experiments of a single evaporating droplet subject to gas flow have also been conducted to provide the first hand data for model comparison. The objective of this paper is to evaluate existing evaporation models with high evaporation rate. A literature review is present firstly to examine the origins of various evaporation models, from classical Spalding diffusion model to those with sophisticated treatment of gas and liquid flows. Particular attention is paid to the treatment of surface blowing effect due to high evaporation rate. The evaporation models obtained from either experiments or theoretical analyses are summarized and carefully examined. The validity of these models is then evaluated by comparing the model predictions with three sets of existing data coming from careful experiments of single droplet evaporation in the literature. It is found that all of the models perform nearly identical for cases with a low evaporation rate, while significant deviations among the model predictions emerge when the evaporation rate is increased. Based on these comparisons, a simplified evaporation model is identified and recommended to cases with high evaporation rates. The comparison also reveals a lack of reliable experimental temperature data for droplet evaporation, particularly in the cases of high evaporation conditions.