Development of liquid-air mass transfer correlations for liquid desiccant dehumidification considering the liquid/air contact and film instability

The focus of this work is on the liquid-air mass transfer mechanism that is critical for liquid desiccant dehumidification and many other absorption processes. Most existing mass transfer correlations heavily rely on specific experiments and show poor universality. Therefore, we proposed a new set of mass transfer correlations theoretically based on the film instability during falling film dehumidification. The flow dynamic, Marangoni effect and liquid/air contact conditions that affecting the interface characteristics and wetting factors are considered. The correlations were verified by comparing with experimental data from several widely-cited literatures. The tests in these literatures were conducted under a wide range of operating conditions and dehumidifier types. The newly-developed correlations provide an acceptable prediction for liquid-air mass transfer, showing close trends to all previous experimental results. The overall error of the new predictions, 20-30%, is close to those of empirical equations built in the specific literature. The factors that affect the interphase mass transfer by changing the film instability and the wetting factor are also analyzed. The increase in liquid Reynolds number shows the most significant effect as it could effectively increase the film instability and liquid-air contact area. The liquid contact angle on solid surfaces, regarding the wettability, also affects the mass transfer considerably. By reducing the contact angle from 90 degrees to 10 degrees, although the increase in Sherwood number is slight due to the suppression of film instability, the wetting factor is almost doubled, resulting in a significant growth in mass transfer performance. This new correlation examines the falling film mass transfer process in more detail, and is based on fewer simplifying assumptions and attempts to take more realistic situations into account. Findings presented herein contribute to a more fully understanding on the falling film behaviors during liquid/gas contact such as liquid desiccant dehumidification. (C) 2019 Elsevier Ltd. All rights reserved.