Article
Chemistry, Physical
Zhifeng Hu, Siyu Ding, Xuan Zhang, Xiaomin Wu
Summary: This study experimentally explores the impact behavior of droplets on superhydrophobic surfaces with single pillars of different sizes. The effects of Weber number and the pillar-to-droplet diameter and height ratios on the contact state between the droplet and solid surface and the maximum width are investigated. The results show that increasing pillar size reduces the maximum width factor of impact droplets, and the critical Weber number for touching the substrate and forming liquid fingers is influenced by the pillar-to-droplet diameter and height ratios. A theoretical model based on energy conservation is developed to calculate the maximum width factor on the single-pillar superhydrophobic surfaces, which agrees well with experimental results within a +/- 10% prediction deviation.
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
(2022)
Article
Chemistry, Physical
Changli Yi, Chengzhi Hu, Lin Shi, Minli Bai, Jizu Lv
Summary: The study found that the transition of the wetting state depends on the joint action of potential coefficient, pillar spacing, and pillar height, with droplets transitioning between Wenzel, Cross, and Cassie states. Cassie formula accurately predicts weaker fluid-solid attraction and smaller pillar spacing, while Wenzel formula predicts stronger fluid-solid attraction and smaller roughness. Additionally, accurate prediction of contact angle is possible when fluid-solid attraction is strong and pillar spacing is small for both Wenzel and Cassie formulas.
APPLIED SURFACE SCIENCE
(2021)
Article
Chemistry, Physical
Jinming Zhang, Wei Ding, Uwe Hampel
Summary: This study deconstructs a complex surface defect into three primary surface defects and uses large-scale Molecular Dynamics simulations to investigate the mechanisms of droplet-solid static friction forces induced by these defects. Three element-wise static friction forces related to the primary surface defects are revealed, and it is found that the static friction force induced by chemical heterogeneity is contact line length dependent while the static friction force induced by atomic structure and topographical defect is contact area dependent. The latter causes energy dissipation and leads to a wiggle movement of the droplet during the static-kinetic friction transition.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
(2023)
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
Multidisciplinary Sciences
Raouf Barboza, Stefano Marni, Fabrizio Ciciulla, Farooq Ali Mir, Giovanni Nava, Federico Caimi, Annamaria Zaltron, Noel A. Clark, Tommaso Bellini, Liana Lucchetti
Summary: In this study, we investigated the electrostatic behavior of ferroelectric liquid droplets on a lithium niobate ferroelectric crystal substrate. The droplets exhibit explosive emission of fluid jets upon entering the ferroelectric phase, mostly at the interface, which eventually form secondary droplets.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Materials Science, Coatings & Films
Yan Zhu, Jialiu Liu, Yongmao Hu, De-Quan Yang, Edward Sacher
Summary: This study evaluated the dynamic water contact performances and drying processes of two commercially available superhydrophilic coatings, revealing that although their static contact angles were essentially the same, their dynamic water droplet behaviors were substantially different. Additionally, the drying times of droplets on the QS200 coating were longer compared to the QS3100 coating.
SURFACE ENGINEERING
(2021)
Article
Chemistry, Physical
Kaikai Li, Yingxi Xie, Biao Tang, Huanwen Ding, Xiaokang Mei, Min Yu, Chunbao Li, Longsheng Lu
Summary: By constructing surface microstructures and improving their hydrophobicity, severe adhesion of biological fluids on surgical electrodes can be effectively reduced. Inspired by purple orchid leaves with self-cleaning properties, the dynamic behavior of water and biological droplets on superhydrophobic microstructured surfaces (SMSs) heated over 100°C was studied. The SMSs with Cassie-Baxter state showed a pseudo-Leidenfrost effect for water droplets, and the dynamic evolution mechanism of plasma droplets on heated surfaces was proposed. The findings contribute to understanding the anti-adhesion mechanism of surgical electrodes at the microscopic level.
SURFACES AND INTERFACES
(2023)
Article
Chemistry, Multidisciplinary
Mehdi H. Biroun, Luke Haworth, Hossein Abdolnezhad, Arash Khosravi, Prashant Agrawal, Glen McHale, Hamdi Torun, Ciro Semprebon, Masoud Jabbari, Yong-Qing Fu
Summary: Droplet impact behavior on solid surfaces is crucial for industrial applications such as spray coating, food production, printing, and agriculture. The challenge lies in modifying and controlling the impact regime and contact time of the droplets, which becomes more critical for non-Newtonian liquids. This study explores the impact dynamics of non-Newtonian liquids on superhydrophobic surfaces and shows that the addition of Xanthan alters the shape and reduces the contact time of the droplets.
Article
Thermodynamics
Jianqiang Hou, Jianying Gong, Xin Wu
Summary: A numerical model was established to investigate the freezing behavior of ellipsoidal water droplets on cold surfaces. The study focused on the spreading behavior, impact force evolution, and heat transfer behavior. The results showed that reducing the aspect ratio of the droplets reduced the contact time on superhydrophobic surfaces, facilitating rebound. Increasing the aspect ratio increased the spreading range, especially on hydrophilic surfaces. The impact force evolution on superhydrophobic surfaces exhibited a double-peak feature, with the first peak decreasing and the second peak increasing as the aspect ratio increased. The heat transfer between droplets and the cold surface was greater for higher aspect ratios, especially on more hydrophobic surfaces. Increasing aspect ratio seemed to be a good choice for rapid freezing applications.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Chemistry, Physical
Long-Zan Wang, An Zhou, Jin-Zhi Zhou, Longquan Chen, Ying-Song Yu
Summary: The study investigated the impact of droplets on polydimethylsiloxane (PDMS) surfaces with varying solid fractions, revealing changes in the upper and lower limits of the Weber number (We) as the solid fraction decreased. The behavior of droplets on surfaces with different solid fractions involved transitions between Cassie-Baxter and Wenzel wetting states, with the development of a novel model to predict the upper limit of impact velocity. Surface roughness was found to significantly influence the contact time of bouncing droplets, with the maximum spreading parameter following a We(1/4) scaling law.
Article
Chemistry, Multidisciplinary
Bhaskarjyoti Sarma, Dipankar N. Basu, Amaresh Dalal
Summary: The dynamics of liquid jets generated by droplet impact on a fractal superhydrophobic surface were investigated. Two different regimes of jets, singular and columnar, were observed depending on the impact conditions. Singular jets were formed at lower impact velocities and low viscosity, with a maximum velocity up to 20 times higher than the impact velocity. Cylindrical air cavities within the droplet played a crucial role in the formation of high-speed singular jets. In contrast, columnar jets were generated through capillary wave focusing at moderate to high impact velocities. The size of columnar jet drops varied nonmonotonically and was influenced by the preceding jetting dynamics. Both singular and columnar jetting events were suppressed at very high viscosities. These findings have implications for various technologies such as microdispensing, thermal management, and disease transmission.
Article
Mechanics
Shi-Zheng Wang, Xianfu Huang, Longquan Chen, Ying-Song Yu
Summary: Water droplets impinging on micro-grooved polydimethylsiloxane surfaces were investigated, and various phenomena including no bouncing, complete rebound, bouncing occurring with droplet breakup, partial rebound, and sticky state were observed depending on the impact velocity and surface roughness. The lower limit of impact velocity for bouncing droplets was determined by balancing the droplet's kinetic energy with the energy barrier caused by contact angle hysteresis. The upper limit of impact velocity was predicted by recording droplet impact at an ultrahigh speed and correlating the transition from complete rebound to bouncing with the wetting state transition. A theoretical model was developed to predict the upper limit of impact velocity by considering the liquid penetration into the micro-grooves. Additionally, the contact time of bouncing droplets decreased with decreasing Weber number, while surface roughness had a minor influence on the contact time in the experiments.
Article
Chemistry, Multidisciplinary
Xinghui Wu, Jiawei Di, Zhen Yang, Yuanyuan Duan
Summary: This study investigates the dynamic spreading process of mixed droplets on chemically heterogeneous surfaces through molecular dynamic simulations. The research finds that the actual component mole fraction in the triple contact region is consistent with the nominal one for R32/R1234yf mixture droplets, but differs for ethanol/water mixture droplets. By using local properties to modify the molecular kinetic theory, the prediction of dynamic spreading of water/ethanol mixture droplets on chemically heterogeneous surfaces can be significantly improved.
Article
Mechanics
Kai Sun, Lingyun Shu, Feifei Jia, Zhe Li, Tianyou Wang
Summary: Vibration on superhydrophobic surfaces is an effective method for removing droplets. This study experimentally investigated the dynamics of droplets on vibrating superhydrophobic surfaces and established a theoretical model to explain the physics behind droplet detachment caused by vibration. It was found that different droplet oscillation patterns exist and the critical condition for droplet detachment depends on the droplet energy compared to the surface adhesion energy. The study also revealed the impact of vibration frequency and amplitude on droplet detachment time.
Article
Nanoscience & Nanotechnology
Jack Dawson, Samual Coaster, Rui Han, Johannes Gausden, Hongzhong Liu, Glen McHale, Jinju Chen
Summary: This study investigates the dynamics of droplets impacting three hydrophobic slippery surfaces and finds that the impact regime strongly depends on the surface properties. The findings provide insights for selecting surface properties to achieve desirable droplet impact characteristics.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Thermodynamics
Min Il Kim, Hyun Sik Yoon
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2020)
Article
Engineering, Marine
Hyun Sik Yoon, Kyung Jin Oh, Hyo Ju Kim, Min Il Kim, Jahoon Moon
Article
Metallurgy & Metallurgical Engineering
Taein Kong, Byung Je Kwak, Jonghyun Kim, Jeong Hun Lee, Sung Hyuk Park, Ji Hoon Kim, Young Hoon Moon, Hyun Sik Yoon, Taekyung Lee
JOURNAL OF MAGNESIUM AND ALLOYS
(2020)
Article
Thermodynamics
Hyun Sik Yoon, Seok Hyun Nam, Min Il Kim
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2020)
Article
Nanoscience & Nanotechnology
Jahoon Moon, Hyun Sik Yoon
Article
Materials Science, Multidisciplinary
Jinyeong Yu, Hongxin Liao, Jeong Hun Lee, Young Hoon Moon, Hyun Sik Yoon, Jonghyun Kim, Taekyung Lee
Article
Engineering, Marine
Hyun Sik Yoon, Seok Hyun Nam, Min Il Kim
Article
Energy & Fuels
Hyun-Sik Yoon, Yoo-Jeong Shim
Summary: The study investigates natural convection for a hot circular cylinder in a cold square enclosure through numerical simulations. Different flow structures are classified based on the position of the cylinder, with four modes observed at Rayleigh numbers of 10^3 and 10^4, and six modes at a Rayleigh number of 10^5. The emergence of new modes at a higher Rayleigh number is characterized by top side secondary vortices and explained through corresponding isotherms.
Article
Multidisciplinary Sciences
Hyun-Sik Yoon, Kyung-Min Park
Summary: The study examined the deformation of the free-surface of two-phase fluid flow in a tank serving as a simplified blast furnace hearth, focusing specifically on the flow of gas and cold molten iron. The presence of porosity was found to contribute to the formation of a viscous finger near the taphole, impacting the interface instability and the velocity of the free surface. The relationship between porosity magnitude and gas break-through time was found to be linear.
Article
Thermodynamics
Hyun Sik Yoon, Jahoon Moon
Summary: This study numerically evaluated the performance of a variable pitch helically twisted elliptical cylinder through large eddy simulation for forced convection heat transfer. The results showed that the VPHTE cylinder can reduce drag, suppress lift fluctuation, and provide smaller total surface-averaged Nusselt numbers over time compared to smooth and HTE cylinders. The VPHTE and HTE cylinders formed inclined elliptical shapes with local peaks of time-averaged Nusselt numbers, and the temperature contour distribution reflected stably elongated shear layers and delayed vortex shedding.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2021)
Article
Engineering, Marine
Seok Hyun Nam, Hyun Sik Yoon
Summary: This study investigates the effects of wavy geometric disturbance on flow around elliptic cylinders with different aspect ratios at low Reynolds numbers. The influence of aspect ratios and wavelengths on flow structures is significant, resulting in the classification of flow states in a bifurcation map.
Article
Engineering, Marine
Janghoon Seo, Hyun Sik Yoon, Min Il Kim
Summary: This study investigates the effect of a wavy duct on the propulsion performance of a propeller by applying the wavy shape on a wake equalizing duct. The results show that the wavy duct can improve the efficiency of the propeller, especially at larger angles of attack and wavenumbers. Compared to traditional ducts, the wavy duct increases the axial velocity in the flow field, improves the uniformity of the upstream velocity distribution, and generates wider distributions of low and high pressures. Additionally, the vortical structures of the wavy ducts are influenced by the duct shape and wavenumber.
Article
Thermodynamics
Hyun Sik Yoon, Seok Hyun Nam, Min Il Kim
Summary: This study investigates forced convection heat transfer around wavy elliptic cylinders with different aspect ratios and wavelengths. The results show that short wavelengths result in quasi-2D thermal structures, while long wavelengths form 3D thermal structures. The thermal characteristics are influenced by the state of the thermal structures. As the aspect ratio decreases, the streamlined shape becomes predominant in stabilizing forced convection.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2022)
Article
Energy & Fuels
Janghoon Seo, Hyun-Sik Yoon, Min-Il Kim
Summary: This study established two different models, based on CNN and ED, to predict the flow and heat transfer characteristics around NACA sections. The models were trained and tested using data from computational fluid dynamics simulations and showed good agreement with the true data. These models can be used to design shapes with higher aerodynamic and heat transfer performance and provide physical interpretation of the performance.
Article
Engineering, Marine
Min Il Kim, Hyun Sik Yoon
Summary: The study utilizes a deep CNN to modify airfoil shapes for improving L/D ratio, based on surface pressure distributions, and successfully predicts shapes with higher L/D and preferable pressure fields through numerical simulations and Cp distribution modifications.
