Effect of nucleation time on freezing morphology and type of a water droplet impacting onto cold substrate. (March 2019)

• Record Type: Journal Article
• Authors: Wang, Liping; Kong, Weiliang; Wang, Fuxin; Liu, Hong
• Is Part Of: International journal of heat and mass transfer. Volume 130(2019)
• Page Start: 831
• Page End: 842
• Publication Date: 2019-03
• Subjects: Supercooled water droplet -- Impact freezing -- Nucleation -- Freezing morphology -- Freezing process -- Cold substrate; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2018.10.142
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Impact freezing for water droplets supercooled deeply is carried out. The nucleation in different dynamic phases has a significant influence on the final freezing morphology. There are multiple freezing morphologies under constant conditions due to the uncertain nucleation time. The relationship between freezing morphology and freezing type is proposed. Three kinds of impact freezing process for room temperature water droplets are observed. Abstract: The freezing morphologies and types for droplets at supercooled (−15 °C) and room temperature (20 °C) to impact onto a cold and polished aluminum substrate are investigated experimentally in this paper. It is found that the nucleation in different dynamic processes has a significant effect on the final freezing morphology and there are multiple freezing morphologies under constant conditions due to the uncertain nucleation time. Thus, based on the final freezing shapes, a basic classification for the different freezing morphologies is presented in terms of basin, pancake and semisphere; and three corresponding freezing types, including instantaneous freezing, non-instantaneous freezing and quasi-static freezing, are proposed based on the nucleation in distinct dynamic phases. Furthermore, the relative number of nucleation drops is taken as a function of time, and then the probability of various freezing morphologies and types in each experimental condition is provided. As a result, for both of the supercooled and room temperature water droplets, although the relative number of nucleation drops have roughly the same variational tendency for impact freezing, the nucleation time and the probability of various freezing morphologies remain different, for example, no basin shapes were attained in the case of room temperature water droplets under the experimental conditions of the current study. Meanwhile, the experimental results show that there are obvious diversities on freezing process. Three kinds of freezing processes, including traditional supercooled water freezing process, are presented for the impact freezing of room temperature droplets, which is mainly determined by the nucleation time. Therefore, for further studies of ice formation, the present results suggest that not only the effect of kinetics and heat transfer but also the influence of the nucleation time should be considered, particularly for the large droplets supercooled deeply.