Min Chen

Electric-field control of heterogeneous ice nucleation is important for anti-icing and cryopreservation, but the mechanism in electrolyte systems remains unclear. The electrofreezing behavior of supercooled 0.1 M electrolyte droplets containing LiCl, KCl, CsCl, and guanidinium chloride was investigated under low static biases from −1.0 to +1.0 V. In all cases, the nucleation temperature varied nonmonotonically with voltage and reached a maximum at an ion-specific optimal bias. Contact-angle and surface-tension measurements showed that macroscopic wettability and bulk interfacial properties are nearly unchanged across the electrolyte series. By contrast, cyclic voltammetry revealed systematic differences in CV-derived areal capacitance that follow the cation hydration sequence, indicating cation-dependent modulation of the compact electric double layer. On the basis of the Gouy–Chapman–Stern framework, a thermodynamic mechanism was developed showing that the applied bias tunes the Stern-layer electric field and regulates the nucleation barrier through field cancellation. The correlation among cation hydration, interfacial capacitance, and optimal nucleation bias establishes a mechanistic link between ion-specific electric-double-layer structure and electrofreezing. These findings provide a physicochemical basis for low-voltage control of interfacial icing.

1. Phase-change heat and mass transfer at liquid–vapour interfaces govern the performance of a wide range of engineering systems, including micro-heat pipes and vapour chambers for high-flux electr...

A fixed-surface heat flux boundary condition was implemented using the Shakhov–Boltzmann kinetic model. Our approach is tested by simulating a fixed heat flux boundary condition in a Micro In-plane Knudsen Radiometric Actuator (MIKRA) device, across the range of Knudsen number (Kn = 0.3–11.49), designed for extreme, vacuum-like environments. Simulation results, compared with laboratory measurements under identical heat-flux conditions, show strong agreement, confirming the model's ability to accurately predict rarefied gas dynamics. Surface temperatures on both hot and cold MIKRA arms are predicted within 1% error for moderate Knudsen numbers (Kn < 4.64), with accuracy decreasing to 3%–5% at higher Knudsen numbers (Kn > 4.64) due to radiative effects beyond the model's conductive framework. Notably, the overall mean absolute percentage error is 2.07%. Experimental force validation indicates the model's improved performance, especially vs Direct Simulation Monte Carlo, in the sensor-relevant Knudsen regime. Our work lays a strong computational foundation for rarefied microscale gas simulation with direct experimental validation. A thorough parametric study addresses accommodation coefficients and microscale rarefaction effects, including one- and two-dimensional flow profiles, velocity contours, and core phenomena like thermal creep and the Knudsen layer. Also, the variation of accommodation coefficients for both arms is discussed, and a comparison is drawn. Parametric analysis reveals that asymmetric accommodation coefficients on hot and cold sensor arms produce a synergistic effect: increasing the hot arm coefficient while decreasing the cold arm coefficient enhances Knudsen effects. The fixed heat flux boundary condition is also compared with the fixed heat flux boundary condition to see the difference in findings.

In this paper, we experimentally investigate the rebound dynamics of droplets on dry ice surfaces, unveiling the mechanism behind the inverse Leidenfrost phenomenon. We demonstrated that the underlying mechanism driving the inverse Leidenfrost phenomenon is the lift force from the air film generated by the sublimation of dry ice. The air film prevents droplet condensation, facilitating the droplet rebound. However, the presence of film significantly depends on impact conditions. During the early spreading stage, bubbles nucleate at the contact line due to the sublimation, then the bubbles grow and gradually form an air film. We showed that the droplet rebound occurs only when the air film fully forms before the maximum spreading stage. Otherwise, the contact line is frozen, ultimately preventing rebound. We propose a theoretical expression of critical air film thickness that determines whether the droplet rebounds. Based on the expression, we ultimately established a theoretical criterion for droplet rebound via thermodynamic and fluid dynamics principles. To validate our developed theoretical criterion, we further investigated the inverse Leidenfrost phenomenon for different fluids, Weber numbers, and different temperatures of droplets. The results demonstrate a high consistency between the predicted results of our theoretical criterion and experimental results.

In this study, a probabilistic method was proposed for an aircraft’s thermal protective layers. The uncertainties of material properties, geometric dimensions, and incoming flow environments were considered for the design inputs. To accelerate the design efficiency, Latin hypercube sampling and surrogate models were built based on finite element method calculations to enhance the simulation efficiency. Thus, the Monte Carlo method can be implemented with such a fast simulation method and produce a massive number of samples for the uncertainty quantification and sensitivity analysis, exploring their impact on the back temperature of the thermal protection layer. Compared to the deterministic method with the extreme deviation design, the probabilistic design yields a weight reduction of 15.61%. This indicates that probabilistic design is an efficient approach to enhance the performance of aircraft and reduce the overall weight of the aircraft. The general goal of this study is to provide a new design method for the coating film of thermal protection systems by considering multiple sources of uncertainties.

The homogeneous condensation of water vapor at ambient temperature is studied using molecular dynamics simulation. We reveal that there is a droplet size at the nanoscale where water droplets can be stabilized in the condensation process. Our simulations show that the growth of water droplets is dominated by collision and coagulation between small water droplets after nucleation. This process is found to be accompanied by exceptionally fast evaporation such that droplet growth is balanced by evaporation when water droplets grow to a critical size, approximately 12.5 Å in radius, reaching a stable size distribution. The extremely high evaporation rate is attributed to the curvature dependence of surface tension. Surface tension shows a significant decrease with decreasing droplet size below 20 Å, which causes the total free energy of nanoscaled water droplets to rise after collision and coagulation. Consequently, water droplets have to shrink via fast evaporation. The curvature dependence of surface tension is related to the dielectric ordering of water molecules near the surface of water droplets. Owing to fast evaporation, secondary condensation occurs, and many small water clusters form, ultimately exhibiting a bimodal distribution of water-droplet size.

In the present work, we study the maximum spreading of bouncing droplets in the capillary regime at ultralow Weber numbers with a fixed static contact angle. In the ultralow Weber number region, experiments reveal that existing spreading laws are inapplicable because of gravity exclusion and change in deformation shape. We propose a theoretical scaling law based on energy conservation, modeling the deformed droplet as an ellipsoid with gravity effects. The proposed scaling law indicates the competition between gravity and inertia at ultralow Weber numbers and distinguishes their dominant regimes. By integrating higher-Weber-number regions, we reveal that viscosity is prominent in the previously assumed inviscid regime. Furthermore, we devise a phase diagram to clarify different impact regimes on the basis of energy analysis.

The rotational dynamics of water near the ice/water interface and its relation with the crystal growth of ice are investigated by using molecular dynamics simulations. We find that the dipole-moment profiles of water adjacent to interfaces display an oscillation behavior, which is in contrast to the monotonic decay near the free surface for water films. This dielectric oscillation phenomenon is associated with the strong response to hard solid/water interface. It significantly suppresses the dielectric relaxation and slows down the rotational diffusion near the interface compared to bulk water. We propose that the rotational diffusion determines the active degree of growth sites on interfaces, and its slowdown due to the interfacial dielectric oscillation contributes to reducing the growth rate of ice. With this idea, we predict the crystal growth rate of ice based on the modified Wilson–Frenkel model involving rotational dynamics. The theoretical result agrees well with the simulation.