Article
Nanoscience & Nanotechnology
Ya-Nan Dong, Ning-Ning Han, Xing-Juan Zhang, Ben-Xi Zhang, Jun-Yao Wang, Xin He
Summary: This study investigates the impact of nanodroplets on wettability-controlled surfaces through MD simulations. It is found that the transportation mechanism for nanodroplets differs from macro-scale droplets, as nanodroplets on hydrophobic/hydrophobic or hydrophobic/superhydrophobic surfaces undergo bouncing instead of breakup. The normalized transportation velocity, V*, is extracted from the MD simulation results and controlled by the difference of contact angles and impact velocity. The study establishes an energy conversion model to quantify the relationship between V* and the contact angle increment.
MICROFLUIDICS AND NANOFLUIDICS
(2022)
Article
Nanoscience & Nanotechnology
Xiaoyan Yu, Hua Lai, Hongjun Kang, Yuyan Liu, Youshan Wang, Zhongjun Cheng
Summary: This study reports the directional self-transportation of water droplets in oil using a TiO2-coated conical spine. By increasing the surface hydrophilicity and utilizing the Laplace force caused by the conical gradient structure, the self-transportation is achieved. The findings of this study provide new ideas for designing new superwetting self-transportation materials.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Chemistry, Physical
Jiayu Du, Yanzhi Li, Xinxin Wu, Qi Min
Summary: In this study, millimeter superhydrophobic stepped surfaces were designed to achieve highly steerable directional bouncing and reduction of contact time for impacting droplets. The experimental results demonstrated that the stepped surfaces outperformed microtextured surfaces in terms of performance.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2023)
Article
Chemistry, Multidisciplinary
M. Aravind, Alina Peethan, Sajan D. George
Summary: By selectively grafting silicone oil onto a glass substrate, a wettability contrast of approximately 43 degrees can be created, allowing for the capture and transport of bubbles underwater and collection of water from mist. This study demonstrates the potential of this method in underwater bubble collection and water harvesting.
Article
Thermodynamics
Liang Guo, Yanling Chen, Ningning Cai, Wanchen Sun, Yuying Yan, Han Wang, Yuheng Gao
Summary: The evaporation processes and morphological developments of diesel droplets impacting on aluminum alloy surfaces with different wettability and temperatures were experimentally investigated in order to improve the controllability of combustion and reduce HC and CO emissions. The research showed that oleophilic surfaces facilitate droplet evaporation, while oleophobic surfaces promote vapor film formation and reduce droplet Leidenfrost temperature. Stronger oleophobicity enhances droplet rebound and secondary breakup, improving evaporation in the gas-phase space and air-fuel mixing. Higher surface wall temperatures improve oleophobicity ability of convex domes, grooves, and protrusions structures on laser-etched surfaces compared to boss/pits and needle-like structures on chemically etched surfaces.
APPLIED THERMAL ENGINEERING
(2022)
Article
Chemistry, Physical
Konghua Yang, Qi Liu, Zhaohua Lin, Yunhong Liang, Chunbao Liu
Summary: This study investigates the directional transportation of droplets using a mixed-wettability surface inspired by kingfishers' feathers. Experimental testing and numerical modelling show that the anisotropic surface can convert vertical impacting to horizontal droplets transport. The intensity and patterns of the thrown droplets are controlled by the wettability and surface offset location. The optimized surfaces can achieve a maximum horizontal transport distance of up to 6.2D0, with a first desorption time of only 7.8 ms. These findings have important implications for engineering designs in anti-icing, lubrication, and spray cooling applications.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2022)
Article
Engineering, Mechanical
Jia Luo, Shuang-Ying Wu, Lan Xiao, Zhi-Li Chen
Summary: This study investigated the mechanism and parameters affecting the contact time of droplet impacting on solid surfaces using numerical simulation method and water spring theory. The results showed that increasing Weber number or decreasing cylinder diameter effectively reduced contact time, with surface wettability having the greatest impact on contact time.
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
(2021)
Article
Mechanics
Lei Xing, Shuai Guan, Minghu Jiang, Longlong Shi
Summary: In this study, the directional transportation of droplets on a surface with controllable wettability was investigated numerically. The mechanisms of directional migration and morphological evolution of droplets impacting on the superhydrophobic-hydrophobic interface were revealed, and the effects of the impacting position on the migration velocity, rebound height, and transport distance of droplets were analyzed. Theoretical models were derived for predicting the transport distance and rebound height of droplets. The simulation results showed different stages in the process of droplet impacting on the superhydrophobic-hydrophobic interface compared to a normal surface. The study also found the existence of an optimal adhesion length for maximizing the transport distance of the droplet. The results contribute to the fundamental theory of droplet directional migration and have practical applications.
Article
Chemistry, Multidisciplinary
Dongdong Xie, Yunna Sun, Yongjin Wu, Kai Wang, Guilian Wang, Faheng Zang, Guifu Ding
Summary: A universal wettability switching strategy is developed for achieving programmable directional transport of both droplets and subaqueous bubbles on a dumbbell-patterned functional surface (DPFS). The switchable superwettability of the material regulates the fluid dynamics within the confined pattern, enabling the construction of multiple channels and imparting the fluidic system with strong robustness against path defects. This energy-consumption-free fluid transport system opens a new avenue for on-chip programmable fluid manipulation, promoting innovative applications requiring rational control of two-phase fluid transport.
ADVANCED MATERIALS
(2023)
Article
Mechanics
Chunfang Guo, Lei Liu, Jianxing Sun, Changwan Liu, Senyun Liu
Summary: This study experimentally investigates the bouncing and splashing of droplets on grooved superhydrophobic surfaces. The research reveals the influence of groove parameters and droplet properties on the critical Weber number for liquid jet splashing. The findings contribute to the understanding of droplet splashing dynamics on textured superhydrophobic surfaces and have potential applications in agriculture and industry.
Article
Thermodynamics
Wen-Zhen Fang, Fang-Qi Zhu, Faquan Shen, Delin Chai, Wen-Quan Tao
Summary: This study explores the freezing behaviors of water droplets impacting super-hydrophilic surfaces at different inclinations and subcooling degrees. The results show that the ice shape and length of rivulets are influenced by the inclination angle and subcooling degree, indicating the coupling effect between the solidification and drop-scale fluid dynamics.
APPLIED THERMAL ENGINEERING
(2023)
Article
Chemistry, Multidisciplinary
Chung-Te Huang, Ching-Wen Lo, Ming-Chang Lu
Summary: This study developed a superhydrophobic surface with a double-reentrant groove (DRG) array, which can suppress the Leidenfrost effect and reduce the contact time of droplets impacting a solid surface at high temperatures.
Article
Chemistry, Physical
David Feldmann, Bat-El Pinchasik
Summary: The adhesion of droplets to surfaces is highly sensitive to the direction of chemical heterogeneities, as shown by bending beam and droplet roll-off experiments. The shape of the fluid contact line on the microscale elucidates the origin of this direction-dependent adhesion. These findings improve the understanding of droplet adhesion to surfaces with chemical heterogeneities and directional transport phenomena.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2021)
Article
Engineering, Aerospace
Fengchao Li, Chunbo Hu, Yu Fu, Guangtao Li, Jiaming Hu, Chao Li
Summary: An experimental system is established to investigate the behavior of burning aluminum droplets impacting a wall in a solid-rocket-motor environment. The rebound process of droplets impinging on the wall is observed, and a formula for predicting the droplet-wall contact time is developed. The total restitution coefficient of droplets is found to decrease with increasing Weber number, and a model for calculating the restitution coefficient is proposed.
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Chemistry, Multidisciplinary
Chunfang Guo, Lei Liu, Rui Yang, Jiangtao Lu, Senyun Liu
Summary: Superhydrophobic surfaces have significant potential for passive anti-icing applications by reducing the contact time between droplets and surfaces. However, their anti-icing performance against supercooled water droplets has not been studied. We fabricated typical post-array and flat superhydrophobic surfaces to investigate the droplet impact dynamics. The contact time and bouncing behavior were systematically studied under controlled temperature, humidity, and surface frost conditions.
Article
Engineering, Aerospace
Yifan Jiang, Jun Zhang, Peng Tian, Tengfei Liang, Zhihui Li, Dongsheng Wen
Summary: The interest in operating satellites in Very Low Earth Orbit (VLEO) is increasing due to their potential applications for Earth observation and telecommunication. This study investigates the effects of atmospheric drag on the attitude control and operational life of satellites in VLEO. The authors use the direct simulation Monte Carlo (DSMC) method to calculate aerodynamic drag and propose drag reduction strategies for VLEO satellites.
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Engineering, Chemical
Sihang Gao, Zhiping Yuan, Xiaomin Wu
Summary: This study investigates the effects of initial velocity and sideslip angle on the jumping velocity, energy conversion, and morphological evolution of coalesced droplets. The results show that both initial velocity and sideslip angle have a negative impact on jumping velocity, and they cause an asymmetric evolution of the droplet morphology.
CHEMICAL ENGINEERING SCIENCE
(2023)
Article
Energy & Fuels
Chen Zhang, Hui Gao, Jiajun Zhao, Jianjun Zhou, Xiaolong Ma, Dongsheng Wen
Summary: In this study, a framework for 2D dynamic coking study is established, and the impact of carbon deposition on flow, heat transfer characteristics, and heat sink is simulated and discussed. The results show that secondary cracking reactions promote the concentration of coking precursors, and the simulated coking results agree well with the experiment. After coking formation, the fluid flow velocity and solid temperature increase, and the heat sink deteriorates, while the maximum conversion of n-decane remains almost unchanged.
Article
Multidisciplinary Sciences
Ran Tao, Wei Fang, Jun Wu, Binhong Dou, Wanghuai Xu, Zhanying Zheng, Bing Li, Zuankai Wang, Xiqiao Feng, Chonglei Hao
Summary: Water droplets detach rapidly from rotating surfaces with micro/nanotextures in a doughnut shape, reducing the contact time by about 40% compared with stationary surfaces. The droplets fragment into satellites and scatter spontaneously to avoid further collision with the substrate. Furthermore, the contact time is highly dependent on the impact velocities of the droplets, surpassing the classical inertial-capillary scaling law. These results not only deepen the fundamental understanding of droplet dynamics on moving surfaces but also suggest a synergistic mechanism to actively regulate the contact time by coupling the kinematics of droplet impingement and surface rotation.
Article
Physics, Applied
Fuqiang Chu, Shuxin Li, Zhifeng Hu, Xiaomin Wu
Summary: Superhydrophobic surfaces are highly promising due to their excellent water repellency in various applications. Droplet impacting dynamics plays a crucial role in the application of these surfaces. This Perspective summarizes the process of droplet impacting on superhydrophobic surfaces and introduces the two key parameters that describe the dynamics, namely the maximum spreading coefficient and the contact time. Improvement strategies such as constructing macrostructures and setting wettability patterns are discussed, highlighting the need to study the combined effects of these factors.
APPLIED PHYSICS LETTERS
(2023)
Article
Computer Science, Interdisciplinary Applications
Kaikai Feng, Peng Tian, Jun Zhang, Fei Fei, Dongsheng Wen
Summary: Recently, a new method called unified stochastic particle (USP) has been developed for simulating multiscale nonequilibrium gas flows. This method, which couples the effects of particle movements and collisions, allows for larger time steps and cell sizes compared to traditional stochastic particle methods. To apply USP to complex nonequilibrium gas flows, a solver called SPARTACUS has been developed within the SPARTA framework, a widely used software for simulating rarefied gas flows. SPARTACUS is parallelized using the message passing interface (MPI), and it is open-source and available with documentation, tutorial examples, and benchmark cases.
COMPUTER PHYSICS COMMUNICATIONS
(2023)
Article
Thermodynamics
Yukai Lin, Fuqiang Chu, Xiaomin Wu
Summary: This study uses moving-mesh numerical simulation to investigate the evaporation of droplets at different wetting modes and finds that the simulation results of mixed mode evaporation agree well with experiments. The effect of wetting modes on the variation of multiple physical fields is elucidated, and the study has promising applications in industrial and technological fields such as thermal management, droplet microfluidics, and medical treatment.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Mechanics
Zhifeng Hu, Fuqiang Chu, Xiaomin Wu, Alfonso M. Ganan-Calvo
Summary: Superhydrophobic surfaces with different shapes and sizes of ridges were investigated for their maximum axial spreading of impacting droplets. A mathematical formula was proposed to describe the shape of the structures using a shape factor for easy application in structure-related studies. The effects of ridge shape and size on the maximum axial spreading coefficient were clarified. The outward flow of liquid above the ridge tip hindered the axial spreading of droplets, and the maximum axial spreading coefficient decreased as the ridge became sharper, achieved by increasing the shape factor or the ridge height-width ratio. The complex effect of the ridge-droplet size ratio was divided into two regimes based on the shape factor. A prediction correlation for the maximum axial spreading coefficient was established, considering the coupled effects of all parameters, and shown to agree well with experimental and simulation results.
Article
Mechanics
Siqi Yao, Fei Fei, Peng Luan, Eunji Jun, Jun Zhang
Summary: The performances of simplified Bhatnagar-Gross-Krook (BGK) models in highly nonequilibrium flows are uncertain. The ellipsoidal statistical BGK (ES-BGK) model outperforms the Shakhov BGK (S-BGK) model in Fourier flow, while the S-BGK model performs better in Couette flow and shock wave. However, both ES-BGK and S-BGK models deviate from the Boltzmann solutions as the Knudsen number or Mach number increases. To improve the performance, the S-BGK model is extended by adding more high-order moments, resulting in the S-BGK+ model with better performance across various flow regimes.
Article
Multidisciplinary Sciences
Yuhang Dai, Minfei Li, Bingqiang Ji, Xiong Wang, Siyan Yang, Peng Yu, Steven Wang, Chonglei Hao, Zuankai Wang
Summary: Liquid metal has been widely used in applications such as flexible electronics and soft robots due to its low melting temperature, good flexibility, and high electrical and thermal conductivity. Researchers have discovered that liquid metal droplets can completely rebound from surfaces covered with a water film of sufficient thickness, and the rebound coefficient increases with the thickness of the water film. This finding advances the understanding of droplet dynamics in complex fluids and provides insights for fluid control.
NATURE COMMUNICATIONS
(2023)
Article
Chemistry, Physical
Yukai Lin, Xiaomin Wu, Zhifeng Hu, Fuqiang Chu
Summary: Despite the extensive research on Leidenfrost droplet motion in its boiling regime, little attention has been paid to the droplet motion across different boiling regimes where bubbles are generated at the solid-liquid interface. In this study, experiments are conducted to investigate the behavior of Leidenfrost droplets on substrates with varying wettabilities and temperature gradients. A novel phenomenon of droplet motion that resembles a jet engine is observed on a hydrophilic substrate, where the droplets repulse themselves backwards as they travel across boiling regimes.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2023)
Article
Chemistry, Physical
Huimin Hou, Xiaomin Wu, Zhifeng Hu, Sihang Gao, Yuxi Wu, Yukai Lin, Liyu Dai, Guisheng Zou, Lei Liu, Zhiping Yuan
Summary: Researchers propose a method for condensate droplet transportation based on the reaction force of superhydrophobic saw-tooth surfaces. Experiments show that this new method improves transport velocity and relative distance compared to conventional methods, and achieves directional transport of the smallest condensate droplet. The superhydrophobic saw-tooth surfaces enable multi-hop directional transport.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2023)
Article
Mechanics
Hao Yang, Jun Zhang
Summary: In this study, a new theoretical framework for the information preservation (IP) method based on kinetic theory is introduced to offer a complete understanding of the preserved information's transport properties. By introducing a velocity-information joint distribution function (VIJDF) and deriving its governing equation as well as the corresponding macroscopic transport equations, the accuracy of the IP method is ensured. Numerical simulations demonstrate that the IP method can achieve similar accuracy as the DSMC method with a much smaller sampling size.
Article
Mechanics
Linying Zhang, Wenjun Ma, Qin Lou, Jun Zhang
Summary: In this study, a new surrogate model (PINN-DVM) is developed to simulate rarefied gas flows by combining physics-informed neural networks (PINNs) with the discrete velocity method (DVM). The linearized Bhatnagar-Gross-Krook equation is directly encoded into the residual of an artificial neural network in the PINN-DVM model. A new loss function for the boundary condition, based on the impermeable diffusion model, accurately captures the velocity slip and temperature jump at the boundary. PINN-DVM overcomes the limitations of conventional numerical methods and exhibits superiority compared to original PINNs in solving rarefied gas flows, as demonstrated by four representative numerical cases.
Article
Physics, Fluids & Plasmas
Hanyi Liu, Jun Zhang, Jia Luo, Dongsheng Wen
Summary: Molecular dynamics simulations were used to investigate the behavior of nanodroplets impacting on superhydrophobic and nanocone-structured surfaces. A model was developed to predict whether the nanodroplets would touch the underlying substrate during impact. The advantages and disadvantages of applying nanocone structures to solid surfaces were revealed by analyzing the restitution coefficient and contact time.