Temperature-gradient effects on heterogeneous ice nucleation from supercooled water

Abstract

Investigating the nucleation and freezing behavior of supercooled water under temperature gradients is of significance for theoretical research and practical application. This paper focuses on the freezing temperature of bulk supercooled water in a rectangular container for which the temperature at two sides can be controlled to present a temperature difference. The experimental results show that the nucleation temperature under temperature differences will be lower than that under isothermal conditions. In addition, an increase in the temperature difference is shown to linearly increase the supercooling needed for ice nucleation. The temperature gradient is capable of suppressing heterogeneous ice nucleation. Based on the classical nucleation theory, the free energy barrier for heterogeneous nucleation is attributed to the main factor to affect the nucleation rate. By comparing theoretical evaluations with experimental results, correction on the free energy barrier was conducted to predict the nucleation rate in the temperature gradient. Our experimental research and theoretical correction reveal the nucleation behavior of supercooled water under nonequilibrium conditions.

Microstructure Enhances the Local Electric Field and Promotes Water Freezing

“…The maximum and average temperature differences before freezing were Δ T max = 4.35 °C and Δ T ave = 4.05 °C, respectively, which were significantly larger than Δ T max = 3.14 °C and Δ T ave = 2.96 °C in a 10 μL droplet on a superhydrophobic surface (151.1°) . The freezing temperature under a big temperature difference will be lower than that under a smaller difference or isothermal conditions . Therefore, the freezing temperature of the water film on PDMS substrates was close to that of small droplets on a more superhydrophobic surface.…”

“…38 The freezing temperature under a big temperature difference will be lower than that under a smaller difference or isothermal conditions. 39 Therefore, the freezing temperature of the water film on PDMS substrates was close to that of small droplets on a more superhydrophobic surface.…”

Suppression of ice nucleation in supercooled water under temperature gradients

“…It can be verified from macroscopic experimental phenomena that a larger degree of supercooling can be obtained when supercooled water is cooled with a temperature difference. [34,37] In order to eliminate discrepancies caused by model simplification and assumptions, more accurate temperature distribution within the cluster and on the interface between the water and ice embryo needs to be studied in depth, and the corresponding strict experiments need to be designed with the help of the relevant numerical simulation and advanced experimental techniques [59][60][61] in future work. Our analysis and results will help us to understand ice nucleation under nonequilibrium conditions in fundamental researches, and to better control the stability of supercooled water by using a temperature gradient in practical applications.…”

“…The similar linearity is also presented in our previous fitted results in the macroscopic experiment of temperature difference affecting the freezing temperature of supercooled water. [37] 2.0…”

“…[34][35][36] In our previous study, we have carried out water freezing experiments to measure nucleation temperature under different temperature differences. [37] The median nucleation temperature is about −16.3 • C during isothermal cooling, but it is −20.1 • C by unilaterally cooling the water initially at an equilibrium state of −5 • C. When nucleation occurs, the median temperature at one side of the supercooled water is the nucleation temperature −20.1 • C and the average temperature at the other side is −6.8 • C. The results showed that the degree of supercooling needed to trigger nucleation in temperature gradients is larger than that in isothermal conditions. Meanwhile, we found that the temperature gradient possibly changes the free energy barrier for nucleation according to the evaluation of nucleation rate.…”