Applicability of vapor pressure models on the prediction of evaporation and motion of sulfuric and hydrochloric droplets in free-falling process

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In acid pickling and electroplating processes, a large number of acid droplets, such as sulfuric droplets and hydrochloric droplets, are emitted from the open tank surface. These two types of droplets are typical indoor pollutants in industrial buildings. They are harmful to personnel, devices, and structures. To effectively remove droplets and evaluate their damage to indoor environments, it is important to accurately predict the evaporation and motion of droplets. Partial vapor pressure at the droplet surface significantly affects droplet evaporation and motion. Hence, in this study, the applicability of different droplet surface partial vapor pressure models on the evaporation and motion prediction of two droplets was numerically investigated. Two widely used models, namely osmotic coefficient method and Van't Hoff factor method, were studied for predicting droplet behavior in a free-falling process. The results indicated that the Van't Hoff factor method exhibited a large deviation in predicting the evaporation and motion of the two droplets. The osmotic coefficient method could accurately predict the evaporation and motion of hydrochloric droplets. However, the prediction of sulfuric droplets demonstrated a sharp change (data mutation), thereby resulting in serious deviation. Furthermore, the results indicated that the conditions that led to data mutation corresponded to a relative humidity less than 62% and a solute mass fraction (ω) greater than 40%. Additionally, different ionization methods of sulfuric solution affected the accuracy of the prediction results. The results can provide guidance for the accurate prediction of the evaporation and motion of sulfuric and hydrochloric droplets.