Solid-liquid Interfacial Wettability Research Articles

Molecular dynamics study of effect of wettability on rapid boiling over copper nanoparticle in water pool

Many special phenomena occur during rapid boiling of a liquid when it is largely superheated near the thermodynamic critical temperature which is much higher than the saturation temperature. However, although there are many experimental work reported the observation of rapid ejection near the surface region of the materials, they are limited in either length or time scales due to the limitation of classical macroscopic theory. In this work, molecular dynamics simulation of heat transfer from nanoparticle to a surrounding liquid pool is carried out to study the effect of solid-liquid interfacial wettability on the boiling phenomena of water around the nanoparticle. The interactions among copper atoms are described by the embedded atom method (EAM) potentials, and the TIP4P water model is used to describe water atoms. The results show that the interfacial thermal conductance is influenced by the interfacial wettability. Increasing the wettability between the particle and the fluid reduces the interfacial resistance. The nucleation of bubbles and formation of vapor occur more quickly for increased solid-liquid interfacial wettability. The results might change due to the uncertainties of the potential functions, therefore further investigation is worthwhile to study rapid boiling of water on nanoparticles using different water models.

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.

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 Study on Explosive Boiling of Thin Liquid Argon Film on Nanostructured Surface Under Different Wetting Conditions

Molecular dynamics (MDs) simulations have been performed to investigate the boiling phenomena of thin liquid film adsorbed on a nanostructured solid surface with particular emphasis on the effect of wetting condition of the solid surface. The molecular system consists of liquid and vapor argon and solid platinum wall. The nanostructures which reside on top of the solid wall have shape of rectangular block. The solid–liquid interfacial wettability, in other words whether the solid surface is hydrophilic or hydrophobic, has been altered for different cases to examine its effect on boiling phenomena. The initial configuration of the simulation domain comprises a three-phase system (solid platinum, liquid argon, and vapor argon), which was equilibrated at 90 K. After equilibrium period, the wall temperature was suddenly increased from 90 K to 250 K which is far above the critical point of argon and this initiates rapid or explosive boiling. The spatial and temporal variation of temperature and density as well as the variation of system pressure with respect to time were closely monitored for each case. The heat flux normal to the solid surface was also calculated to illustrate the effectiveness of heat transfer for different cases of wetting conditions of solid surface. The results show that the wetting condition of surface has significant effect on explosive boiling of the thin liquid film. The surface with higher wettability (hydrophilic) provides more favorable conditions for boiling than the low-wetting surface (hydrophobic), and therefore, the liquid argon responds quickly and shifts from liquid to vapor phase faster in the case of hydrophilic surface. The heat transfer rate is also much higher in the case of hydrophilic surface.

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.

Nanoscale study of boiling and evaporation in a liquid Ar film on a Pt heater using molecular dynamics simulation

Molecular dynamics simulations have been conducted to understand the mechanism for bubble formation on a platinum substrate with particular emphasis on the surface texture. Liquid Argon, that follows the model of Lennard–Jones fluids, is the fluid of interest. The nano-sized bubbles are formed under different degree of superheat and surface conditions. The bubble nucleation and vapor film formation show dependence on the degree of superheat and solid–liquid interfacial wettability. A bubble does not form easily on a non-wetting surface. It is easy to nucleate a bubble on a smooth surface for higher degree of superheats. The hydrophilic surfaces provide favorable conditions for bubble nucleation and formation of vapor films.

Molecular dynamics simulation on bubble formation in a nanochannel

Molecular dynamics simulations are carried out to examine the bubble behavior confined in a nanochannel with particular emphasis on the nucleation phenomenon. Simple Lennard-Jones fluids are under consideration and nano-sized bubbles are observed under different conditions of solid–liquid interfacial wettability. It is found that the bubble nucleation behavior shows a marked dependence on the solid–liquid interfacial interaction. In particular, it is found that bubbles appear in the bulk liquid homogenously for a hydrophilic surface, but grow directly on a hydrophobic solid surface. Also, a bubble will not form on a non-wetting surface. A nanobubble exists stably under the equilibrium state and the number density distribution of the curved liquid–vapor interface is examined. It is also found that there are few vapor atoms in the nano-sized bubble and the internal vapor pressure of the nanobubble is much lower than that required from the Young–Laplace equation. The disagreement with the prediction of the Young–Laplace equation can be attributed to the fact that the liquid–vapor interface region plays an important role on the force balance at the curved liquid–vapor interface of a nanobubble.