Liquid Argon Film Research Articles

Rapid boiling of ultra-thin liquid argon film on patterned wettability surface with nanostructure: A molecular dynamics investigation

Surface wettability and structure have been proved as two important influential factors to the thermal transport at the solid-liquid interface at nano scale, however, the combined enhancement mechanism has not been clearly understood till now. In this study, the rapid boiling behaviors of nano thin liquid argon film on the heterogeneous wetting surfaces were examined with the non-equilibrium molecular dynamics (MD) method. Meanwhile, the ring-patterned and stripe-patterned surfaces were designed and analyzed, respectively. By analyzing the trajectory of argon atoms, the bubble nucleation behavior, heat flux and interfacial thermal resistance, it is found that the lower hydrophobic area fraction is favorable for the bubble formation and the ring-patterned surface shows an advantage in the nucleate boiling compared with the stripe-patterned one. Meanwhile, the nanostructure has a great influence on the boiling phenomena, which accelerates the development of bubble nuclei and improves the maximum heat flux compared with the planar one. In present simulations, the ring-patterned surface with nanostructure of 40% hydrophobic area fraction is the optimal design for the efficiency enhancement of explosive boiling process. The findings in this work contribute to the design of the coating nanostructured surface to enhance the boiling heat transfer performance under the high heat fluxes.

Molecular dynamics data-driven study of leidenfrost phenomena in context to liquid thin film phase transformation

In many micro and nanoscale applications of thin film phase transition, identifying the circumstances that allows stable liquid contact with a heated surface is critical. Using molecular dynamics (MD) simulations, our current data driven machine learning-based study attempts to examine the properties of liquid interaction with a solid surface at nanoscale. A few nanometer-thick liquid argon layer over a platinum surface has been used to simulate a liquid-solid contact system. The wall temperature is raised linearly after necessary initial equilibration of the entire system, with different boundary heating rates for various surface wetting conditions, namely hydrophobic, hydrophilic, and superhydrophilic. Our current investigation shows that the heating condition, liquid film thickness, and surface wetting condition all have a significant impact on the type of liquid wall contact that persists during the phase transition phenomena of thin liquid argon film (i.e., normal evaporation or explosive boiling). In the event of normal evaporation, a stable liquid contact with the solid surface continues, however in the case of explosive boiling, the liquid film is splashed away from the solid surface resembling the macroscopic Leidenfrost effect. For various system configurations in regard to liquid initial film thickness, liquid heating rate as well as solid-liquid interaction, a wide variation of the onset time as well as the wall temperature of boiling explosion have been found in the present study. An accurate mapping of the Leidenfrost conditions in context to nanoscale thin film liquid-vapor phase process has been generated using a predictive model based on deep neural networks that has been designed, trained and cross validated against molecular dynamics data of the present study.

Nanoscale investigation of surface wettability distribution on bubble nucleation with variable temperature boundary condition

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.

Effects of Heat Source Temperature, Nanostructure, and Wettability on Explosive Boiling of Ultra-Thin Liquid Argon Film Over Graphene Substrate: A Molecular Dynamics Study

Background: The study on explosive boiling phenomenon has received increasing attention because it involves many industries, such as advanced micro-, nano-electromechanical and nano-electronic cooling systems, laser steam cleaning, and so on. Objective: In the present work, the explosive boiling of ultra-thin liquid film over two-dimensional nanomaterial surface in confined space with particular emphasis under the three different influencing factors: various heights of nanostructures, various wetting conditions of solid-liquid interface as well as various heat source temperatures. Methods: Molecular Dynamics simulations (MDs) in present work have been adopted to simulate the whole explosive boiling process. Results: For different heat source temperature case, the higher the heat temperature is, the less time the explosive boiling spends after relaxation. For nanostructure case, nanostructure surface significantly increases heat transfer rate and then leads to the increase of phase transition rate of explosive boiling. For different wetting property case, the increase of surface wettability results in an increase of phase transition to some degree. Conclusion: The addition of nanostructures, the higher heat source temperature and good wettability between thin liquid film and substrate surface dramatically improve thermal heat transfer from solid surface to liquid film, which will give rise to explosive boiling occur. In addition, the non-vaporized argon layer still exists in these three factors despite continuous thermal transmission from the substrate surface to liquid argon film adjacent to the solid surface even other vaporized argon atoms.

Molecular dynamics study on the effect of hydrophilicity on thin film evaporation over biphilic surface

The objective of this study is to understand the effect of surface wettability and how nano-scale heat transfer is affected by different surface wetting conditions over biphilic surface by molecular dynamics simulations. The system of 3 nm liquid Argon film over Platinum surface is equilibrated at 90 K and then wall temperature is raised to higher value to study the effect of temperature. According to this study at low wall temperature and low surface wetting conditions, liquid temperature increases proportionally with the increment of hydrophilic portion but at higher wall temperature and better surface wetting conditions, maximum value of liquid Argon temperature increases with increasing hydrophobic portion. Evaporation number, evaporative mass flux and heat flux increase significantly with slight increment of hydrophilic portion. Inception time decreases with increasing hydrophilic portion and surface wettability. Also, for better surface wetting conditions, average evaporative mass flux is more sensitive to wall temperature and increases significantly at higher wall temperature.

Molecular dynamics study on explosive boiling of ultra-thin liquid over solid substrate: considering interface wettability of Argon/MoS2

ABSTRACTA molecular dynamics (MD) study is carried out to reveal the phenomenon about the normal and explosive boiling of ultra-thin liquid argon film absorbed on MoS2 surface with different wetting conditions. The three-phase molecular system is composed of a solid MoS2 wall, a liquid argon film and a vapour argon region. Initially, the three-phase simulated system is thermally equilibrated at a low temperature. Then the MoS2 heat source is suddenly heated up to two different high temperatures those far above critical point of liquid argon, and the argon experienced a phase transition process in the NVE ensemble. The simulation results show that the good wetting properties and high heat source temperature dramatically enhance phase transition efficiency, accelerating the heat transfer rate, shortening the boiling time, and increasing the evaporation rate, and they have remarkable effects on temperature and pressure histories, density distribution during whole boiling process. Explosive boiling is more likely to occur at high superheated degree, but evaporation occurs at low superheated degree. In addition, at a high superheated degree, it can be conclude from the simulation results that the better wetting properties of the solid-liquid interface is, the shorter time of the explosive boiling is needed.

Effect of Solid Properties on the Process of Bubble Nucleation: a Molecular Dynamics Study

Nucleation boiling is used in a wide range of engineering and science fields, such as electronics cooling, new energy and the microelectromechanical systems (MEMS) technology. Besides, a better understanding of the nucleation is fundmental significance for the application and enchcement of nucleation boiling in the traditional and modern high-tech industries. Unfortunately, due to the complexity of physical mechanisms in nanoscale and the limit of small scale, accurate experimentation of nucleation cannot be accomplished. Therefore, it is important to study the influence of solid properties on nucleation despite its general importance by performing molecular dynamics simulation researches. In present work, we succeed in simulating the nanoscale boiling of liquid argon film on the solid surface, and the solid properties are varied to test their effects on bubble nucleation. The simulation results show that the bonding strength between solid atoms and the solid atomic mass has a radically different effect on nucleation while they have little effect on the contact angle between liquid and solid atoms. If the value of the bonding strength is too large, the liquid and solid phases will hardly interact with each other and too little heat will be transferred to form a bubble nuclear. On the other hand, if the value of the bonding strength is too small, it will be easy to appear explosive boiling and be hard to form a stable vapor bubble. For the solid atomic mass, the result is the opposite of the bonding strength. The smaller the value of the solid atomic mass, the harder nucleation on the solid surface. Due to the variations of the solid atomic mass and the bonding strength between solid atoms leads to a difference in the vibrational density of state (VDOS) of the solid atoms, meaning a difference in the thermal vibrational coupling between solid and liquid atoms, and thus appearing the different boiling phenomenon.

Atomistic modelling of thin film argon evaporation over different solid surfaces at different wetting conditions

In the present study, non-equilibrium molecular dynamics (MD) simulations have been performed to reveal the effect of solid–liquid interfacial wettability on the evaporation characteristics of thin liquid argon film placed over the flat solid surface. The atomistic model considered herein comprises of a three-phase simulation domain having a solid wall over which liquid argon and argon vapour co-exist. Initially, the system is thermally equilibrated at 90 K for a while after which rapid increase in the solid wall temperature induces a phase change process, i.e. evaporation. Both hydrophilic and hydrophobic wetting conditions of the solid surface have been considered at an evaporation temperature of 130 K for three different surface materials such as platinum, silver, and aluminium. The simulation results show that both the surface wettability and surface material have a significant role in phase transition phenomena of thin liquid film, particularly the surface wettability for the present system configuration. The thermal transport phenomena between the wall and liquid thin film have been studied thoroughly and discussed in terms of wall heat flux, evaporative mass flux, upper bound of maximum possible heat flux etc. The results obtained in the present MD simulation study are compared with the macroscopic predictions based on classical thermodynamics. Interestingly, a very good agreement has been found indicating that macroscopic thermodynamics approach can predict the characteristic of phase change phenomena of nanoscale thin liquid film.

Molecular dynamics simulation of bubble nucleation on nanostructure surface

In this paper, the bubble nucleation of ultra-thin liquid argon film on a platinum surface is studied by molecular dynamics simulation. In the simulations, the liquid is heated by the middle part and cooled by the two sides of the platinum surface. Observation of bubble nucleation is performed after increasing the temperature of heating zone. The space and time evolution of argon density distribution and the size of bubble are monitored to investigate the nucleation processes above surfaces with and without nanostructures. The results illustrate that nanostructure surface increases the solid-liquid contacting area and the degree of surface temperature non-uniformity, which results in the enhancement of heating intensity and higher rate of nucleation. Comparisons are made among surfaces with different nanostructures, with which it is further found that the heat flux increases with the height of nanostructures. Higher nanostructure reduces nucleation duration.

Influence of interface wettability on normal and explosive boiling of ultra‐thin liquid films on a heated substrate in nanoscale: a molecular dynamics study

Wettability, as one of the important properties of solid surface, may influence heat and mass transfer in boiling process. Molecular dynamics method is employed to investigate the effects of wettability on normal and explosive boiling of ultra-thin liquid argon film absorbed on a heated solid aluminium surface in a confined space in present work. The initial three-phase molecular system is comprised of solid aluminium wall, liquid argon and vapour argon and is run for three different solid–liquid interfacial wettability (lyophilic, lyophobic and neutral surfaces), which achieves a balance at 90 K. After equilibrium period, two different jump temperatures degree, 150 and 350 K, are set on heat source layers separately to characterise the boiling phenomena, namely, low-temperature degree for normal boiling and high-temperature degree for explosive boiling in which temperature of solid wall is far beyond the critical temperature of liquid argon. The simulation results indicate that the wetting condition of solid–liquid interfacial surface have significant effects on both cases of boiling phenomena. Furthermore, the heat transfer rate with good wettability (lyophilic) is much higher than bad wettability (lyophobic) with same jump temperature degree.

Phase Change Characteristics of Ultra-Thin Liquid Argon Film over different Flat Substrates at High Wall Superheat for Hydrophilic/Hydrophobic Wetting Condition: A Non-Equilibrium Molecular Dynamics Study

Non-equilibrium molecular dynamics simulations have been conducted to understand the effect of solid-liquid interfacial wettability and surface material on the phase change phenomena of the thin liquid argon film placed over flat substrate at high wall superheat. The molecular system consists of a three phase simulation domain involving solid wall, liquid argon and argon vapor. After the system is thermally equilibrated at 90K and kept in equilibrium for a while, a high wall superheat (250K that is far above the critical temperature of argon) is induced at the liquid boundary so that the liquid undergoes ultrafast heating. Both hydrophilic and hydrophobic surfaces were considered in the present study in order to observe the effect of surface wettability on phase change characteristics for three different solid substrate materials namely, Platinum (Pt), Silver (Ag) and Aluminium (Al). Results obtained in the present study are discussed in terms of transient atomic distribution inside system domain, heat flux characteristics across the solid-liquid interface together with evaporative mass flux from liquid argon. Simulation results show that, depending on the surface wetting condition, the phase change process appears to be very different (explosive/ diffusive) for all three substrate materials under consideration. Among three materials considered herein, Al is found to offer the least favourable condition for phase change process while Pt and Ag show similar heat and mass transfer characteristics for both hydrophilic and hydrophobic wetting conditions. Surface wettability effect is found to be more prominent than the effect of substrate material in thin film liquid phase change phenomena.Journal of Chemical Engineering, Vol. 29, No. 1, 2017: 49-55

Molecular dynamics simulation on explosive boiling of liquid argon film on copper nanochannels

Phase change from liquid to vapor of the working fluid has been widely used in thermal control for microelectronic devices. In this study, the effects of nanochannels on the explosive phase transition of ultrathin liquid argon film on the copper substrate in confined space are investigated through molecular dynamics simulation. The results show that nanochannels significantly facilitate the thermal energy transfer from solid copper surface to the liquid argon which leads to a much more violent explosive boiling than the plain surface. Liquid argon atoms adjacent to the solid surface are instantly overheated and consequently a cluster of liquid argon detaches from the surface once the explosive boiling occurs. The temperature of the liquid argon when it separates from the solid surface increases with respect to the increasing nanochannel heights, while the time for the system to reach equilibrium decreases distinctly. Furthermore, though continuous heat transfers to the liquid argon, a non-vaporized layer always exists near the bottom surface of the solid copper base with a stable number density of about 0.0251/Å3.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate.

Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures’ height in a certain range.

Molecular Dynamics Study of Effect of Different Wetting Conditions on Evaporation and Rapid Boiling of Ultra–thin Argon Layer Over Platinum Surface

Molecular dynamics simulations have been conducted to reveal the effect of solid-liquid interfacial wettability on the boiling phenomena of the thin liquid argon film placed over solid platinum wall. The three phase molecular system is comprised of solid platinum wall, liquid argon and argon vapor. Initially the three phase system is thermally equilibrated at 90K and after the attainment of equilibrium the temperature of solid platinum wall is suddenly increased which resembles ultrafast pulse heating. Two different degree of superheat have been considered to characterize the boiling phenomena, namely, evaporation for low degree of superheat and rapid or explosive boiling for high degree of superheat in which temperature of the wall was far above the critical temperature of argon. The solid-liquid interfacial wettability is varied to observe its effect on boiling and thus simulations are run for hydrophilic, hydrophobic and neutral surfaces. The simulation results show that surface wettability has a significant role on both cases of boiling phenomena. The nucleation of bubbles and formation of vapor films occurs more quickly for increased solid-liquid interfacial wettability. The study shows that hydrophilic surface is the most favorable surface condition for bubble nucleation.

A comparative study by the grand canonical Monte Carlo and molecular dynamics simulations on the squeezing behavior of nanometers confined liquid films

Grand canonical Monte Carlo (GCMC) and liquid-vapor molecular dynamics (LVMD) simulations are performed to investigate the squeezing and phase transition of a simple liquid argon film confined between two solid surfaces. Simulation results show that the LVMD simulation is capable of capturing the major thermodynamic equilibrium states of the confined film, as predicted by the GCMC simulations. Moreover, the LVMD simulations reveal the non-equilibrium squeeze out dynamics of the confined film. The study shows that the solvation force hysteresis, observed in many surface force experiments, is attributed to two major effects. The first is related to the unstable jumps during the laying transitions of the confined film, in which the gradient of force profile is larger than the driving spring constant. The second effect is related to the squeeze out dynamics of the confined film even though the first effect is absent. In general, these two dynamic processes are non-equilibrium in nature and involve significant energy dissipations, resulting in the force hysteresis.

Effect of nanotextured array of conical features on explosive boiling over a flat substrate: A nonequilibrium molecular dynamics study

Nonequilibrium molecular dynamics simulations were performed to investigate the effects of size of nanocone array and types of wall material, i.e., aluminum and silver, on the explosive boiling of ultra-thin liquid argon film on nanostructure. An Embedded Atom Method (EAM) potential is used in describing the interatomic interaction between metal atoms. The results showed that the cone-like nanostructures drastically enhance heat transfer from solid to liquid and they have significant effects on temperature and pressure histories, net evaporation number, as well as the density distribution in the system. In all cases studied, the liquid molecules above the solid surface go into explosive boiling and a cluster of liquid is observed to move upward. It was also observed that the separation temperature associated with separation of liquid film from solid surface strongly depends on size of nanostructure while it is not sensitive to the type of materials. Furthermore, in all cases in a specific time after beginning of boiling, the evaporation on the hot wall stopped and a non-evaporating layer will form on the surface.

Molecular dynamic simulation of platinum heater and associated nano-scale liquid argon film evaporation and colloidal adsorption characteristics

A novel ‘fluid–wall thermal equilibrium model’ for the wall–fluid heat transfer boundary condition has been developed in this paper to capture the nano-scale physics of transient phase transition of a thin liquid argon film on a heated platinum surface and the eventual colloidal adsorption phenomenon as the evaporation is diminishing using molecular dynamics. The objective of this work is to provide microscopic characterizations of the dynamic thermal energy transport mechanisms during the liquid film evaporation and also the resulting non-evaporable colloidal adsorbed liquid layer at the end of the evaporation process. A nanochannel is constructed of platinum (Pt) wall atoms with argon as the working fluid. The proposed model is validated by heating liquid argon between two Pt walls and comparing the thermal conductivity and change in internal energy to thermodynamic properties of argon. Later on, phase change process is studied by simulating evaporation of a thin liquid argon film on a Pt wall using the proposed model. Gradual evaporation of the liquid film occurs although the film does not vaporize completely. An ultra-thin layer of liquid argon is noticed to have “adsorbed” on the platinum surface. An analysis similar to the theoretical study by Hamaker (1937) is performed for the non-evaporating film and the value of the Hamaker-type constant falls in the typical range. This analysis is done to quantify the non-evaporating film with an attempt to use molecular dynamics simulation results in continuum mechanics.