Nucleation in supercooled water triggered by mechanical impact: Experimental and theoretical analyses

Abstract

Supercooling is one of the major drawbacks that hinder the wide application of phase change thermal storage technology, where supercooling needs to be suppressed, or nucleation triggered at desired supercooling or time. The disturbance of mechanical impact can effectively promote nucleation. However, up to now, its nucleation mechanism has not been well explained, and the corresponding nucleation triggering technology has not been reasonably developed. In this paper, the effect of mechanical impact in supercooled water on nucleation is investigated experimentally by impact rod falling freely to hit the bottom of container. The nucleation temperature under impact at different heights of free fall are measured. The results show that 80% supercooling reduction can be achieved by a low impact energy of 0.007 J. In addition, we modify the existing model based on the experimental data to develop a revised model, which can estimate the impact stimulus required to trigger nucleation at desired supercooling. Moreover, the nucleation mechanism under impact based on classical nucleation theory is analyzed. By comparing the changes in pre-exponential factor and nucleation barrier with and without impact, the enhancement in nucleation rate under impact can be explained as a reduction on the free energy barrier for nucleation. Our experimental and theoretical analysis results preliminarily reveal the impact nucleation mechanism, which are expected to promote more in-depth research on the related topics. These results could also better serve to predict whether nucleation will occur in the supercooled water under mechanical impact, and to actively trigger nucleation or suppress supercooling as needed through mechanical impact.