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Icephobic material is of great importance in power transportation, communication, aerospace, and so on. Bionic lotus superhydrophobic surfaces show good application prospects in anti‐icing by repelling impacting droplets. However, the boundary (criterion) between droplet bounce and deposition on superhydrophobic surface under cold freezing rain is unclear. Here, from the view of statistics, the boundary and internal heat transfer mechanism of the droplet bounce, pinning, and three kinds of deposition including icing at later, early retraction, and spread. are clarified Droplet viscosity increase reduces droplet contact with surface and inhibited splash at high We. Surfaces with temperature above −20.6 °C showed 100% droplet bounce after impact on We = 64.7, and the probability of water adhesion and ice nucleation decreases to ≈0%, resulting in completely anti‐icing. Droplet bounce transition mainly ascribe to the decrease retraction driven force caused by interface freezing and transition temperature increases approximately linearly from −25.9 to −21.1 °C within 21.6 < We < 75.5. Ice nuclei brought by condensation in humid environment (60–100 RH%) further cause droplet eccentric retraction and transition temperature increases to −6 to −10 °C. The fundamental understanding of droplet behaviors on supercooled superhydrophobic surface is beneficial for icephobic surfaces applications. [ABSTRACT FROM AUTHOR]

Abstract Icephobic material is of great importance in power transportation, communication, aerospace, and so on. Bionic lotus superhydrophobic surfaces show good application prospects in anti‐icing by repelling impacting droplets. However, the boundary (criterion) between droplet bounce and deposition on superhydrophobic surface under cold freezing rain is unclear. Here, from the view of statistics, the boundary and internal heat transfer mechanism of the droplet bounce, pinning, and three kinds of deposition including icing at later, early retraction, and spread. are clarified Droplet viscosity increase reduces droplet contact with surface and inhibited splash at high We. Surfaces with temperature above −20.6 °C showed 100% droplet bounce after impact on We = 64.7, and the probability of water adhesion and ice nucleation decreases to ≈0%, resulting in completely anti‐icing. Droplet bounce transition mainly ascribe to the decrease retraction driven force caused by interface freezing and transition temperature increases approximately linearly from −25.9 to −21.1 °C within 21.6 < We < 75.5. Ice nuclei brought by condensation in humid environment (60–100 RH%) further cause droplet eccentric retraction and transition temperature increases to −6 to −10 °C. The fundamental understanding of droplet behaviors on supercooled superhydrophobic surface is beneficial for icephobic surfaces applications.

The investigation of carbon dioxide (CO 2) condensation on heat exchange surfaces is essential to the advancement of carbon capture, utilization, and storage (CCUS) technology. Molecular dynamics simulations are employed to explore the wetting and condensation behavior of CO 2 on nanostructured surfaces. The results indicate that the contact angle of CO 2 droplets on nanostructured surfaces is greater than that on smooth surfaces. Increasing the pillar height (h) or solid fraction (f) induces the transition of CO 2 droplets from the Wenzel to Cassie state, resulting in an increased contact angle. Nanostructured surfaces significantly enhance the nucleation rate, with molecules initially nucleating at the bottom of the pillars. A higher h or f accelerates the nucleation rate during the condensation. Droplets in the Wenzel state exhibit higher heat transfer efficiency than those in the Cassie state. Additionally, the formation of Cassie-state CO 2 droplets undergoes a dewetting transition, altering the heat conduction mode. The dewetting behavior of CO 2 droplets favors their detachment from the surface, potentially reducing the initial heat resistance. Therefore, appropriately increasing h and f can promote nucleation and droplet growth, enhancing dewetting transition and mass transfer performance. These simulation results hold great importance for inspiring the design of future CO 2 -phobic surfaces and guiding CO 2 condensation production. • Dropwise condensation of CO 2 on pillar-structured surfaces was first studied by MD. • Alterations in structural dimensions can regulate the wetting behavior of CO 2 droplets. • A thermal resistance model was developed to analyze heat transfer in various states. • Nanostructured surface improves the heterogeneous condensation and nucleation. • The CO 2 nucleation mechanism was explained by the potential energy distribution. [ABSTRACT FROM AUTHOR]

Measurement campaigns at the high mountain Observatory Mt. Cimone (CMN; 2165 m a.s.l.) were performed during May 2014 and October 2015. The concentration of Ice Nucleating Particles (INPs) were measured offline with a dynamic filter processing chamber (DFPC), in the deposition and condensation mode, after collecting PM 1 and PM 10 aerosol samples. Presented INP data are the first ever published for a high mountain site in the Mediterranean basin. During the May campaign, parallel INP measurements were also carried out at San Pietro Capofiume (SPC), a low altitude rural background area within the Po Valley basin, by the same offline technique. The average INP PM10 concentration at CMN was 86 m −3 (saturation ratio S w = 1.01; T = −18 °C) during the May 2014 campaign, while it was 171 m −3 at SPC, in the same period. A lower average INP PM10 concentration was observed at CMN during October 2015 (43 m −3 ). A significantly higher activated fraction (AF) characterized the October 2015 campaign, suggesting that the seasonal changes in the aerosol sources have an impact on the INP efficiency of the aerosol at CMN. Super-micrometer INP contributed for ∼30% of total INP in the May 2014 campaign, at both sites, and for ∼70% in the October 2015 campaign, showing the importance of coarse particles in the INP population. The analysis of meteorological parameters, gaseous tracers concentrations and backwards trajectories suggests that the INP population at CMN is contributed by transport processes occurring at diverse spatial scales, from the local to the synoptic scale. During the Saharan Dust transport Event observed in May 2014, a reduction of the AF was observed, suggesting, for this case, a limited ice nucleating activity for Saharan dust particles. This may be due to physico-chemical aging of the Saharan dust particles during transport or to the relatively high activation temperature at which the experiments were performed in this study. [ABSTRACT FROM AUTHOR]

• A Rayleigh scattering method is used to characterize water clusters. • The pictures of the clusters evolution and distribution characteristics are drawn. • The exact size order of the clusters in the stable distribution layer is carried out. • Mechanism of microstructure and condensation conditions effect on clusters is deduced. Through Rayleigh scattering light intensity measurement, this paper investigates the transition state characteristics and microscopic evolution mechanism of the vapor water aggregate into liquid water in a narrow space near the subcooling wall. With the experimental analysis, clusters distribution layers with different characteristics in the several hundred microns width region near the condensation wall are found, especially the layer in which the average clusters size may maintain at a stable level. Since the same-sizes clusters layer, a relatively stable cluster diffusion region forms, and the size of the clusters diffusing from the region is evaluated to be about dozens of water molecules. The experimental analysis also shows that the cluster distribution and diffusion process in the near wall region are affected by condensation conditions and wall microstructure, which will further enrich the micro mechanism of the condensation nucleation process, even bring new methods to intensify the process. [ABSTRACT FROM AUTHOR]

The study of vapor condensation on surface has important engineering significance. The condensation nucleation process of vapor on substrates with different pillar structures is studied through molecular dynamic simulation. The condensation droplets on the pillar with various heights and solid fractions exhibit Wenzel state, Cassie state and the transformation from Wenzel state to Cassie state. The results show that the condensation efficiencies are correlated with the state of droplet and it is explained from the perspective of heat transfer. For the Wenzel state, the droplet fills the gap of pillar and the form of the heat conduction change with the growth of cluster. In the initial of condensation droplets, the heat conduction is similar with various heights of pillar. As the condensation droplets grow, the efficiency of heat conduction enhances with the increasing of height of pillar. For the Cassie state, the form of heat conduction is perpetual during the condensation process with the thermal resistance of the droplet dominated due to the droplets suspended on the pillar. The efficiency of heat transfer is insensitive to the height of pillar. The form of heat conduction for the transformation state transforms from Wenzel state to Cassie state leading to the reduction of condensation rate. The droplet formed in the Wenzel state has the higher transfer efficiency than the Cassie one. Image 1 • Condensation of vapors on surface with nanostructure is studied to research the influence of structure parameters. • The growth process of condensation droplet on nanostructure surface is analysis and exhibit the final droplet state. • We construct a thermal resistance model to analyze the heat transfer and condensation efficiency with various states. [ABSTRACT FROM AUTHOR]

Laboratory generated aerosols and aerosol sampled in a field campaign were studied to assess the repeatability of heterogeneous ice activation processes and verify if the ice nuclei particles maintained their nucleating capability. Experiments were performed using a filter technique, i.e. aerosol particles were sampled on black-gridded cellulose nitrate membrane filters and assessed for ice nucleating particles in a dynamic filter-processing chamber at our ISAC-CNR laboratory. The laboratory investigations used Arizona Test Dust (ATD) generated by nebulizing a suspension of ATD. After nebulization, the wet aerosol in the carrier gas was dried and then sampled on a filter. Aerosol field sampling (size range PM1 and PM10) was carried out in the Arctic (Ny-Ålesund, Svalbard) from 12 to 23 April 2019. The activation processes were repeated twice for each filter at temperatures of −22 °C and −18 °C. For aerosol, ATD runs were performed only in conditions of supersaturation (saturation ratio S w = 1.02), while for the Arctic aerosol, conditions below saturation were also considered (S w = 0.96). The experiments showed that approximately 40% of the ATD particles maintain their initial nucleating efficiency, both at T = −22 °C and − 18 °C, and at S w = 1.02, i.e. in the condensation freezing mode. The percentage of repeatability was higher for ATD with respect to the Artic-sampled aerosol processed in the condensation mode. This may depend on greater particle morphology variation of the mixed organic-inorganic aerosol due to the hydration and dehydration cycle. • Experiments showed that about 40% of ATD particles maintains the nucleating efficacy. • The repeatability was higher for ATD with respect to aerosol sampled in Arctic. • Variation of ice nucleating capability of the aerosol has atmospheric implication. • The ice nucleation shows both stochastic and deterministic behavior. [ABSTRACT FROM AUTHOR]