Ping Cheng

Shanghai Jiao Tong University | SJTU · Department of Mechanical Engineering (ME)

The curvature and temperature dependency of the liquid-vapor surface tension has a significant influence on the accurate prediction of the nanobubble/nanodrop nucleation process. In this work, a mesoscopic approach combining the pseudo-potential multiphase lattice Boltzmann method (LBM), the principle of dynamic similarity, and the van der Waals th...

Those various cross-sectional vessels in trees transfer water to as high as 100 meters, but the traditional fabrication methods limit the manufacturing of those vessels, resulting in the non-availability of those bionic microchannels. Herein, we fabricate those bionic microchannels with various cross-sections by employing projection micro-stereolit...

The PP scheme (primitive pseudopotential-based scheme), the MP scheme (modified pseudopotential-based scheme) and the IVD scheme (improved virtual-density scheme) are the three most widely used contact angle schemes in pseudopotential lattice Boltzmann (LB) models to simulate wetting characteristics of multiphase flow over solid surfaces under isot...

Various methods for solar energy utilisation are being developed for reducing the emission of CO2 from fossil fuels, and perfect solar absorbers are attracting increasing attention. In the present study, a metamaterial solar absorber is proposed. The absorber consists of an array of Ni notched nanorings that are periodically arranged on a gold subs...

Nanoscale liquid-vapor interfacial transport phenomena are of great significance to a variety of applications including evaporation, condescension, boiling and micro/nano-fluidics. In this work, we propose a mesoscopic approach to describe the nanoscale liquid-vapor interfacial statics and dynamics by combining the pseudopotential multiphase lattic...

Coalescence-induced bubble departure is a common phenomenon in boiling and gas evolution reactions, which has significant impacts on the heat/mass transport. In this work, we systematically investigate the effects of dynamic contact angles on the coalescence and departure processes of two equal-sized bubbles. A critical contact angle (θcr) of 76° i...

We propose a multi-materials solar absorber consisting of regularly arranged cross resonators made of Ni, and nanocylinders made of Ti on their four corners. The finite difference time domain (FDTD) method is used to study the absorption performance of solar energy, the inherent absorption mechanisms and influencing factors of the absorber submerge...

A modified dimensionless pseudo-potential lattice Boltzmann method capable of restoring all related thermophysical properties of any working fluid and spatial/temporal scales of the computational domain is developed in this work. Direct numerical investigations of ultrathin liquid film evaporation of R143a within nanoporous membranes to its ambient...

Hydrogels are attracting enormous interests in various applications including electronic skins, tissue engineering, drug delivery, and wearable devices due to their marvelous stretchability, conductivity and ultra-high sensitivity. In the present study, we propose a new type of conductive cross-linked hydrogel fabricated by projection microstereoli...

The key problem that hinders the water transportation performance and application of microchannels is the annoying gaslock. Realizing liquid transport without the gaslock requires a specially designed pump and a channel system, as well as the reduction of gas concentration in liquids. In nature, to eat viscous nectar with high efficiency, hummingbi...

A variable solid-fluid interaction strength scheme compatible with the lattice Boltzmann method is introduced to investigate contact angle hysteresis phenomena numerically. This method is applied to study two problems: (i) droplet sliding on inclined isothermal plates and (ii) droplet evaporating on horizontal heated plates. It is demonstrated that...

Smart windows with tunable optical properties in response to external environments are being developed to reduce energy consumption of buildings. In the present study, we introduce a new type of 3D printed hydrogel with amazing flexibility and stretchability (as large as 1500%), as well as tunable optical performance controlled by surrounding tempe...

The solar water evaporation, which can be utilized for seawater desalination and wastewater treatment, promises freshwater security with renewable energy. Herein, we propose a bionic solar evaporator consisting of a hydrogel solar absorber and bionic microchannels fabricated by projection micro‐stereolithography (PμSL) based 3D printing technique....

The boiling crisis determines the maximum heat flux for the safe operation of boiling equipment, which is widely used in various applications including power generation, thermal management of electronics and water desalination. Here we present a mechanistic and predictive theory for the boiling crisis, combining the thermo-fluidic interaction betwe...

Droplet evaporation is a widely encountered heat and mass transfer phenomenon. Due to its 3D in nature, it is challenging to simulate the complex 3D droplet evaporation process. Here, we propose an axisymmetric lattice Boltzmann (LB) model to simulate the dynamics of contact line motion during sessile droplet evaporation on a flat heated surface, t...

In this paper, simultaneous heat and mass transport in porous media is studied numerically using a 2D multicomponent/multiphase phase-change lattice Boltzmann scheme. This newly developed LB model requires no correlation equations as inputs for physical properties of the porous medium (such as relative permeability, heat capacity, thermal conductiv...

A water droplet's impact and its subsequent spreading, recoiling and freezing on a smooth substrate at a supercooled temperature is studied numerically using a 3D pseudo-potential lattice Boltzmann method, in combination with a solid-liquid phase-change model with volume expansion of water at 0°C taken into consideration. Simulated results show tha...

In this paper (Part II of a paper series), a 3D pseudo-potential lattice Boltzmann method in combination with a solid-liquid phase change model with volume expansion taken into consideration (the same model used in Part I) is applied to study a water droplet's impact and its subsequent freezing patterns on rough supercooled substrates, consisting o...

Understanding the dynamics during freezing of nanofluid droplets is of importance from both fundamental and practical viewpoints. It is known that a universal pointy tip is formed on the top of a frozen water droplet [Marín et al., Phys. Rev. Lett. 113(5), 054301 (2014)]. Here, we report that the formation of a pointy tip is broken down due to the...

Nanoparticles deposition dynamics and deposition patterns in evaporating nanofluid droplets on a smooth hydrophilic heated substrate in a vapor environment (0.9Tc) under zero gravity are investigated numerically by a 2D immersed boundary-lattice Boltzmann method in combination of the non-isothermal Gong-Cheng liquid-vapor phase change model. The Ma...

A 3D printed adhesive and conductive hydrogel with super-anti-freezing property is reported. This hydrogel exhibits excellent stretchability (elongation up to 3920%), outstanding adhesive behavior (adhesion strength of 61 kPa), as well as marvelous anti-freezing ability (glass transition temperature as low as -96.3°C). The present 3D-printed hydrog...

Condensation frost is one of the most common types of icing encountered in nature and industrial ap- plications, while its accretion induces multiple non-negligible negative impacts. Many passive anti-/de- frosting approaches by tailoring surface topology and chemistry have been reported recently. To date, however, reliable engineered surfaced that...

It is a great challenge to fabricate a surface with Cassie-Baxter wettability that can be continuously adjusted from hydrophilicity to superhydrophobicity by changing of geometric parameters. In this paper, we propose and demonstrate a bioinspired surface fabricated by using a projection micro-stereolithography (PμSL) based 3D printing technique to...

Nucleation site distribution is ubiquitous in many natural and industrial processes, such as liquid-to-vapor phase change, gas-evolving reactions, and solid-state material growth. However, a comprehensive understanding of nucleation site distribution remains elusive. These limitations are due to the challenge of probing micro/nanoscopic nucleation...

Conductive hydrogels with high stretchability can extend their applications as a flexible electrode in electronics, biomedicine, human-machine interfaces, and sensors. However, their time-consuming fabrication and narrow ranges of working temperature and working voltage severely limit their further potential applications. Herein, a conductive nanoc...

In the present study, interactions between nanoparticles and advancing ice-water interfaces are systematically investigated by molecular dynamics simulations with TIP4P/2005 water model. The criteria for the determination of pushing and engulfing transition are discussed according to Zener's pinning theory and simulation results. Due to the pinning...

In this paper, effects of non-uniform temperature in the ice nucleus on heterogeneous ice nucleation are investigated via two approaches: changes in Gibbs free energy function and availability function. Analytical expressions for non-uniform temperature distribution inside the ice nucleus and heat transfer from the nucleus to the supercooled wall a...

The relationship between bubble departure frequency and diameter is fundamental to the boiling process and needs to be fully understood for prediction of overall boiling heat transfer performance. Hydrody-namic models for bubble departure were developed in previous studies. However, these models could not explain the dependence of bubble frequency...

Boiling is a ubiquitous process in many applications including power generation, desalination, and high-heat flux electronic cooling. At the same time, boiling is a complicated physical process involving hydrodynamics and interfacial heat and mass transfer on multiple scales. One of the key limiting factors of boiling is the critical heat flux (CHF...

The wettability transition of an ion-beam-etched micro-pillar array surface is reported in the present study. The micro-pillar array, made of negative photoresist SU-8, was fabricated by ultraviolet lithography. The results indicate that the combination of the micro-pillar array and ion-beam etching technique can easily regulate surface wettability...

In this paper, the absorptance of a broadband nearly perfect absorber, consisting of a metal surface covered by a rough Bi2Te3 layer, was measured and the optical properties of such a sample are calculated by using the finite-difference time-domain (FDTD) method. The results show that the measured absorptance of a designed sample with a roughness o...

The 3D problem of spreading and solidification of a molten solder droplet (with a melting temperature of Tm and a radius of Rd) on a circular pillar (with a radius Rpillar and a height Hpillar, having a contact angle θpillar at wall temperature Tpillar) above a substrate has important applications in electronic packaging. In this paper, effects of...

Distinct from monoporous structures with only one characteristic pore size, biporous structures are characterized by two distinguished pore sizes. In this paper, novel double-layered biporous coatings consisting of a biporous top layer and a monoporous base layer are fabricated by freeze casting from aqueous nickel slurry, where the particle size (...

Vapor bubble coalescence in saturated pool boiling of nanofluids containing moderately hydrophilic nanoparticles (θ=33∘∼51∘) is investigated numerically by a single component multiphase particle suspension lattice Boltzmann model. It is shown that the vapor bubble coalescence time in a nanofluid is prolonged by the presence of moderately hydrophili...

Owing to superior properties and low cost, carbon felts are widely used in flow batteries as versatile porous electrodes, through which liquid electrolyte is usually pumped to transport reactants/products. In operation, electrochemically/physically induced gas evolution occurring inside the carbon felt is almost inevitable which, even though seems...

In this paper, we numerically investigated the evolution of flow pattern inside an evaporating sessile drop using a transient numerical model based on the Arbitrary Lagrangian–Eulerian (ALE) frame that fully couples fluid flow and heat and mass transfer. Effects of both liquid volatility and initial contact angle on the transient flow pattern were...

A novel continuous directional freeze casting technique derived from LMC (liquid metal cooling) is developed in the present study, which is named as “LMC-like freeze casting”. In this novel freeze casting method, a quartz mold containing slurry is dipped into a low-temperature bath with a constant rate to achieve directional freezing of the slurry....

Six-fold symmetric ice dendrite growth in subcooled water is investigated based on a GPU-accelerated hybrid lattice Boltzmann (LB) method and the cellular automation (CA) method. A reduction factor is proposed to reduce the discretization induced anisotropy in the hybrid method. The accuracy and feasibility of this hybrid method is validated by com...

A perfect absorber, with pyramidal nanostructures made of a natural hyperbolic material, for solar energy harvesting is proposed in this chapter. A numerical investigation is first carried out for regularly arranged bismuth telluride (Bi2Te3, an anisotropic and natural hyperbolic material) pyramidal nanostructures placed on top of a Ag substrate, a...

The two-phase flow, heat transfer and pressure drop of distributed jet array impingement boiling of HFE-7000 on pin-fin surfaces are investigated with particular emphasis on the characteristics, triggering mechanism and affecting factors on two-phase flow instability. It is found that the two-phase flow in a jet chamber becomes unstable at certain...

A three-dimensional lattice Boltzmann phase-change study is carried out on dry spot characteristics in pool boiling on micro-pillar and micro-cavity hydrophilic heaters under constant bottom wall temperature conditions. The degree of superheat and geometry of these micro-structures (i.e., the pitch distance p, the height h, and the width d) are fou...

Nanobubble nucleation by plasmonic heating on a gold spherical nanoparticle under laser illumination is numerically investigated by a 3D liquid-vapor phase change lattice Boltzmann (LB) method. A volumetric heat source is incorporated to the evolution equation of temperature distribution function to simulate photothermal energy conversion effect in...

A guidance structure mounted above a heating surface is proposed to enhance pool boiling heat transfer in this paper. The basic idea is to form separated vapor-liquid pathways with a rising slug flow and a replenishing liquid impingement vertically onto the heating surface through an integrated bubble pump. Visualization and heat transfer experimen...

In this paper, the newly developed multi-component multi-phase (MCMP) lattice Boltzmann method (LBM) is extended for direct simulation on effects of ambient humidity of air and wall temperatures on sessile droplet evaporation. The effect of repulsive strength between gas component and moisture component is taken into consideration by proposing an e...

A solid-liquid local thermal non-equilibrium lattice Boltzmann model for hydrodynamics and heat transfer in a nanofluid is developed in this paper. In this proposed model, interactions between fluid and solid nanoparticles, random motion of nanoparticles as well as heat transfer between nanoparticles and the base fluid are taken into consideration....

The novel solid-liquid local thermal non-equilibrium lattice Boltzmann model, developed in Part I of this paper series [1], is applied to the classical problem of natural convection of nanofluids in a square enclosure with vertical walls at differential temperatures. Effects of Rayleigh numbers, nanoparticles random motion, nanoparticles volume fra...

Pool boiling heat transfer from smooth horizontal hydrophilic and hydrophobic heaters having a finite thickness under constant bottom wall temperature conditions is simulated numerically with a three-dimensional liquid-vapor phase-change lattice Boltzmann method. For a small heater, single bubble dynamics and temporal variations of heater’s top wal...

The evaporation heat transfer of a loop heat pipe (LHP) flat evaporator with porous wick is numerically simulated at pore scale using an advanced phase-change Lattice Boltzmann Method (LBM). The effects of heat flux and surface wettability (contact angle) on the patterns and dynamics of liquid-vapor interface, liquid volume fraction, temperature di...

Fluid flow and heat transfer characteristics of two kinds of binary hydrate slurries CO2-TBAB and CO2-THF in a horizontal tube are investigated experimentally. It is found that CO2-TBAB hydrate slurry shows Herschel-Bulkley (H–B) fluid characteristics at low flow velocity (<0.35 m/s) and as a dilatants fluid at high flow velocity (>0.45 m/s). On th...

Condensation in the presence of non-condensable gas on a biomimetic pillared subcooled surface with hybrid wettability (with hydrophilic top and hydrophobic side and bottom) is investigated using a newly developed 3D multi-component multiphase lattice Boltzmann model. Three preferred nucleation sites with different surface wettability contrasts are...

Pool boiling heat transfer from four types of micro-pillar heat sinks with different wettability patterns is simulated numerically with the latest version of liquid-vapor phase-change lattice Boltzmann model. Effects of pillar geometry and wettability on bubble dynamics are investigated. It is found that bubbles will nucleate either on the hydropho...

The confined jet impingement boiling experiments are conducted with HFE-7000 as coolant to compare bubble dynamics and heat transfer characteristics of normal and distributed jet arrays on smooth surfaces and pin-fin surfaces, respectively. It is found that in single-phase regime, the two jet arrays have almost the same heat transfer coefficient (H...

Molecular dynamics simulation is used to investigate condensation of Argon vapor on nanopillar array surfaces made of copper. It is shown that condensation in the pillar array is nonuniform with respect to height. Effects of pillar height, pitch distance of nanopillars, wall subcooling and wettability on condensation of Argon vapor are discussed. I...

A molten droplet impacting and solidifying on a cold substrate with micro-pillars on the top is studied numerically in this paper using a newly developed multi-component, triple-phase solidification 3D lattice Boltzmann method (LBM). Simulated results confirm that droplets on a rough surface can exist in three states, depending on the static contac...

The latest version of the newly developed liquid-vapor phase-change lattice Boltzmann method, with a conjugate thermal boundary condition imposed at the solid-fluid interface, is applied to simulate numerically pool boiling from smooth, infinitely long, upward-facing, horizontal heated surfaces under controlled wall temperature conditions. A parame...

In this paper, a novel 3D lattice Boltzmann method (LBM) is proposed for simulating a molten droplet impacting and solidifying on a cold smooth substrate surrounded by air. The numerical simulation shows that a small pocket of air is entrapped in the molten droplet adjacent to the cold surface after its impact on the surface. And this trapped air c...

An experimental investigation is carried out on periodic single bubble growth and departure from a small heater in boiling of nanofluids. The nanofluids are made of moderately hydrophilic silica nanoparticles (having a contact angle of 35–37°), dispersing in deionized water at mass concentrations of 0.05%, 0.1% and 0.15%, respectively. It is found...

Numerical simulations of film boiling heat transfer on a horizontal surface are conducted in this paper using a modified pseudo-potential liquid-vapor phase change lattice Boltzmann model. A conjugate heat transfer problem , including heat conduction in the heater and its thermal responses during the film boiling process, is investigated. Unlike pr...

A multi-component/multi-phase (MCMP) lattice Boltzmann method (LBM) with vapor/liquid phase change is proposed in this paper. Two equations of state (EOS) including Peng-Robinson (PR) EOS for water and ideal gas EOS for the non-condensable gas (NCG) are applied in the thermal equation. Based on this newly developed MCMP phase-change LB model, the p...

A perfect absorber design is proposed here that uses a periodic array of pyramidal nanostructures, made from a natural hyperbolic material bismuth telluride (Bi 2 Te 3) on a substrate. A numerical study is carried out to investigate the absorption of solar radiation and to determine the suitable ranges of the geometric parameters for the proposed s...

Microgravity effects on pool boiling heat transfer from a horizontal hydrophilic surface under constant wall temperature are simulated numerically based on an improved liquid-vapor phase-change lattice Boltzmann method with the imposition of a conjugate thermal boundary condition at solid/liquid interface. Effects of microgravity on bubble departur...

The liquid-gas and liquid-liquid Taylor flows in circular capillary tubes are numerically studied using a mathematical model developed in the frame of Arbitrary-Lagrangian–Eulerian (ALE), where the interface is tracked so that the important interfacial curvature and forces for Taylor flow can be accurately estimated. It is found that for liquid-gas...

Effects of surrounding medium, materials (including core–shell configuration) and geometry (size and shape) of nanoparticles on solar energy absorption are studied numerically by employing Mie theory and finite-difference time-domain method. It is shown that nanoparticles, having a high absorption peak in the visible region and a broad absorption b...

In order to enhance the solar thermal energy conversion efficiency, we propose to use carbon-gold core-shell nanoparticles dispersed in liquid water. This work demonstrates theoretically that an absorbing carbon (C) core enclosed in a plasmonic gold (Au) nanoshell can enhance the absorption peak while broadening the absorption band; giving rise to...

Effects of heater's thermal properties and vapor phase's thermal conductivity on saturated pool boiling above a large horizontal heater are simulated numerically based on an improved pseudo-potential liquid-vapor phase change lattice Boltzmann model. A transient conjugate heat transfer problem is under consideration, where the conjugate thermal bou...

In this paper, a novel 3D laser cutting numerical model is developed based on the lattice Boltzmann method, providing a new approach to simulate this process numerically. The proposed model consists of two parts: (i) a thermal enthalpy based solid-liquid phase change model is applied to simulate the melting phenomenon occurring on the solid work pi...

Mesoscale simulations for pool boiling curves and boiling hysteresis on hydrophilic/hydrophobic surfaces, under constant wall temperature/constant wall heat flux conditions, are presented in this paper. It is found that simulated boiling curves in dimensionless form under these two different heating modes are identical in nucleate boiling and film...

MEMS-based micro heat pipes (MHPs), as a novel heat pipe technology, is considered a promising choice for thermal management applications in microelectronic circuits packaging, concentrating photovoltaic cells, infrared detectors, laser diodes, etc. This paper presents a comprehensive review on recent developments and advances in different types of...

Transition from dropwise to filmwise condensation of a dry saturated vapor on downward-facing smooth subcooled horizontal hydrophobic walls with hydrophilic spots is simulated numerically using the newly developed phase-change lattice Boltzmann method. Dynamic behaviors including growth, coalescence and departure of condensate droplets from cooler...

In this paper, a droplet of saturated liquid impacting and freezing on a wall at cryogenic temperatures is numerically investigated based on a newly developed triple-phase lattice Boltzmann method. Effects of initial falling velocity of the droplet as well as temperature and static contact angle of the wall on freezing speed and total volume of ice...