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In this study, the effect of nanostructure morphology on bubble nucleation of liquid argon on a platinum solid surface was explored using molecular dynamics methods. We examined the differences in nucleation behavior on smooth and nanostructured surfaces, including trapezoidal, rectangular, and reentrant cavities. The simulation results demonstrated that nanostructured surfaces outperformed smooth surfaces in terms of bubble nucleation, and the corresponding morphology had a significant effect. The reentrant cavity had the shortest bubble initial nucleation time, followed by the rectangular cavity, and the trapezoidal cavity had the longest bubble initial nucleation time. The mechanism of bubble nucleation on solid surfaces was further investigated from two perspectives: heat transfer through the solid-liquid interface and the potential energy constraint. Compared with other surfaces, surfaces with reentrant cavities exhibited a significantly higher heat transfer efficiency. The liquid atoms on the nanostructured surfaces absorb a large amount of heat within a short time, resulting in rapid accumulation of heat in the cavity. The thermal motions of the liquid atoms are enhanced, and the potential energy constraints from the surrounding atoms are overcome to achieve rapid bubble nucleation. Thus, the nanostructures promote bubble nucleation in the heated liquid. Our results provide novel insights into the design of nanostructures to improve the boiling heat transfer performance. [ABSTRACT FROM AUTHOR]

Abstract Nanostructures have a crucial impact on bubble nucleation. In this paper, different nano-grooved surfaces are constructed using complex trigonometric functions, and the nucleation process of liquid argon on the surfaces is investigated using molecular dynamics simulations. The nanostructures affect the bubble nucleation location, and the results show that the bubble nucleation always occurs in the groove region during the boiling process. In contrast, the bubbles on the flat surface appear randomly. In addition, bubble growth is also affected by the nanostructure. Increasing nanostructure size can reduce the bubble nucleation time and enhance the bubble growth rate. The nanostructure increases the solid-liquid interface area, which enhances the heat transfer between solid and liquid. Finally, the reasons for bubble nucleation on different nanostructured surfaces are analyzed. The heat transfer between solid and liquid is the leading factor for bubble nucleation when the difference in liquid atoms’ potential energy is slight. As the nanostructure size increases, the substrate attracts more argon atoms to form a non-evaporating liquid layer, improving heat transfer and promoting bubble nucleation. [ABSTRACT FROM AUTHOR]

Surface wettability plays an essential role in bubble nucleation. In this article, the molecular dynamics simulation method is conducted to study the bubble nucleation of liquid argon film on a copper substrate with hybrid wettability. Unlike the constant temperature boundary condition, the variable temperature boundary condition is adopted to simulate the bubble nucleation process. The temperature gradually increases from 86 K to 200 K, so the substrate temperature at the bubble nucleation time can be obtained. The potential energy, kinetic energy, total energy, and temperature during bubble nucleation are analyzed. The results show that bubble nucleation occurs when the kinetic energy exceeds the potential energy barrier. A method is used to capture the bubble nucleation process, described from the perspective of total energy. The initial nucleation time of the hybrid wettability surface gradually reduces with the rise of the proportion of the hydrophilic part. Compared with the pure hydrophilic surface, the hybrid wettability surface can achieve faster initial nucleation time and lower nucleation temperature by altering the proportion of wettability. The potential energy and temperature distribution reveal the microscopic mechanism of bubble nucleation. This study provides theoretical guidance for the design of cooling surfaces of micro/nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Surface wettability plays an essential role in bubble nucleation. This paper investigates the phase transition behaviour of argon films placed on inhomogeneous wettability substrates using molecular dynamics simulations. The location of bubble nucleation and initial nucleation time is investigated to reflect the effect of hydrophobic area fraction of inhomogeneous wettability surfaces on bubble nucleation. The results show that the bubbles appear first on the hydrophobic part of the inhomogeneous wettability surface. The relationship between hydrophobic area fraction and initial nucleation time is nonlinear. The initial nucleation time first decreases and then increases as the area of the hydrophobic region increases. In addition, the bubble nucleation process is restricted when the hydrophobic occupation is relatively large on inhomogeneous wettability surfaces. At last, the mechanism of bubble nucleation on inhomogeneous wettability surfaces is discussed in combination with the restrictive relationship between heat absorption and solid–liquid interaction energy. The amount of heat absorption does not directly determine the bubble nucleation. Bubble nucleation can arise in the location with a lower surface energy barrier once the heat absorption can overcome the solid–liquid interaction energy. [ABSTRACT FROM AUTHOR]

The kinetics of homogeneous nucleation of the vapour-gas phase was studied by the molecular dynamics (MD) method in Lennard-Jones systems simulating solutions with partial (A) and complete (B) solubility of components. The calculations were carried out at a temperature close to the normal boiling point of the solvent, two concentrations of the solute, and negative pressures. The pressure, as a function of density and concentration, in stable and metastable states, the parameters of phase equilibrium at a flat interface were determined. The ultimate stretching Δpn = ps–pn exceeded than those calculated from the classical nucleation theory at concentrations of solute c > 0.14 and were less theoretical ones at c < 0.2 in solutions A and B, respectively. A qualitative difference in the formation and growth of the vapour-gas nucleus in solutions A and B was established. In solution A, the partial density of the solvent sharply decreases and the density of the volatile component increases at the region of the bubble formation. In solution B, the density of the volatile component inside the bubble remains close to the density in the surrounding phase, and the density of the solvent decreases at the initial stage of bubble formation. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is conducted to study the effects of surface wettability on rapid boiling and bubble nucleation over smooth surface. The simple L-J liquid is heated by smooth metal surface with different conditions of wettability in cuboid simulation box. The results show that surface wettability has significant impact on phase transition of liquid film. When the heating temperature is 200 K, the rapid boiling occurs above strongly hydrophilic and weakly hydrophilic surfaces; however, only slow evaporation phenomenon occurs above weakly hydrophobic surface within 2.5-ns simulation time. The reason is that the interaction between argon and platinum atoms is stronger over hydrophilic surface, which has higher efficiency in heat transfer. Furthermore, based on the difference of surface wettability in heat transfer efficiency, the surface with nonuniform wettability is constructed, and the central region is more hydrophilic than surrounding region. The growing process of bubble nucleus can be completely observed above the more hydrophilic region. [ABSTRACT FROM AUTHOR]

Rapid heating or sudden depressurization can create highly superheated liquid conditions in stationary or flowing liquid in nanochannels. In these situations, the phase stability of the liquid and the conditions for the onset of bubble nucleation are important factors in the fluid behavior and heat transfer in applications. In the investigation summarized here, a statistical thermodynamics analysis is used to derive a modified version of the Redlich-Kwong fluid property model that accounts for attractive forces between the solid wall surface atoms and liquid molecules in the fluid within a high aspect ratio (parallel plate) nanochannel. In this model, the wall–fluid attractive forces are quantified in terms of Hamaker constants, which makes it possible to assess the effect of wall–fluid force interactions on the spinodal conditions for a variety of fluid and surface material combinations. At large channel widths the fluid properties exhibit wall effects very near each wall, with bulk fluid property values being predicted in the center of the channel. As the channel width decreases, the fluid in the center of the channel begins to feel the effects of both walls and the properties deviate from the bulk values throughout the channel; importantly, the spinodal temperature increases significantly above the bulk fluid value. The results of this analysis imply that in nano- and micropassages and near walls with nano- to microscale roughness, fluid may experience a stabilizing effect due to its proximity to nearby walls, which may, in turn, inhibit bubble nucleation. [ABSTRACT FROM AUTHOR]

Stress whitening pretreatment on expandable acrylonitrile (AN)/methacrylic acid (MAA) copolymer was adopted to reduce the cell size of high-performance AN/MAA copolymer foam. The article studied the influence of stress whitening on cell structure and mechanical properties of AN/MAA copolymer foam, observed foaming behavior of stress- whitened copolymer by hot stage optical microscopy, and discussed its bubble nucleation mechanism. The results indicate that stress-whitening pretreatment makes the cell size of corresponding copolymer foam reduce sharply when stress whitening occurs. The cell size of copolymer foam with the density of 32 kg/m3 and 75 kg/m3 reduces from 1.07 mm to 0.37 mm and from 0.59 mm to 0.076 mm, respectively. It also causes residual fragmental films in cells. The defects created by stress whitening work first as a bubble nucleus, then expand and combine together as cells. Stress whitening creates new interface between gas and polymer phase and new volume of gas phase, reduces the change of interface free energy and volume free energy during bubble nucleation, and improves the bubble nucleation rate. The foaming phenomenon of stress whitened copolymer is in line with the defect nucleation mechanism. However, stress whitening pretreatment reduces the mechanical properties of final foam because of residual fragmental films. [ABSTRACT FROM AUTHOR]

Bubble nucleation and growth are the key steps in polymer foam generation processes. The mechanical properties of foamed polymer are closely related to the size of bubbles created inside the material. Thus, it is necessary to study how to improve mechanical strength by producing extremely fine bubbles inside polymer resin. We developed a theoretical framework to help produce uniformly distributed microcellular bubbles and experimentally verified the theoretical analysis results using an injection molding machine modified to make microcellular foaming products. [ABSTRACT FROM AUTHOR]

In this study, micro square polysilicon heaters having dimensions of 65 × 65 μm 2 and 100 × 100 μm 2 were fabricated on a silicon dioxide layer, and bubble nucleation experiments on the heaters were performed. Bubble nucleation temperature was measured using a bridge circuit, and the photographs of bubble nucleation and subsequent growth were taken by a 35-mm camera with a μs flash unit. Measured bubble nucleation temperatures were found to be closer to the superheat limit of the working fluid of FC-72. A quasi-1-D solution obtained from the 2-D heat diffusion equation yielded proper temperature distribution of the square heaters at steady state; however, it failed to predict the temperature rise up to the steady state. The time-dependent temperatures similar to the observed values can be obtained with much lower value of thermal diffusivity than the bulk property of the polysilicon heater used. For the 100 × 100 μm 2 square heater, nucleation of several bubbles was observed, but for the 65 × 65 μm 2 heater, only that of one bubble was observed. [ABSTRACT FROM AUTHOR]

Extensive studies of vapor bubble in water on microbubble growth and collapse process on microheaters with heat fluxes of 1.2, 1.4, and 1.6 GW/m 2 are performed. The 4 μs heat pulse is applied to 30 × 30 μ m 2 , 30 × 60 μ m 2 , and 20 × 60 μ m 2 heaters for undergone the nucleate boiling. Sequential images during the micro bubble growth process are recorded by the microscopic flow visualization method coupled with phase-averaged technique. The analysis of the top view images show that the increase of aspect ratio of rectangular shape heater changes the bubble shape into ellipsoid with larger ratio of axes, slower rates of bubble growth and collapse, longer bubble lifetime, later time to reach maximum size but play small roles on incipience nucleation, and vapor formation temperature. While the change of high heat flux shifts the incipience time at nucleation temperature, time to vapor sheet formation, time to reach maximum size and thus the bubble lifetime. With side view of bubble images, not only histories of extension of bubble in height but also histories of the contact angle can be provided. Therefore, the correlations of contact angle/surface tension force and boundary moving speed of bubble boundary as well as the determination of major driving mechanism in bubble growth/collapse process can be identified. [ABSTRACT FROM AUTHOR]