scholarly journals Numerical Simulation of Single-Droplet Dynamics, Vaporization, and Heat Transfer from Impingement onto Static and Vibrating Surfaces

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 188
Author(s):  
J. Thalackottore Jose ◽  
J. F. Dunne
Keyword(s):  
Heat Transfer ◽  
Impact Velocity ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Droplet Evaporation ◽  
Time Interval ◽  
Initial Contact ◽  
Droplet Impingement ◽  
The Impact ◽  
Minimum Impact

A numerical study is presented to examine the behavior of a single liquid droplet initially passing through air or steam, followed by impingement onto a static or vibrating surface. The fluid dynamic equations are solved using the Volume of Fluid method, which includes both viscous and surface tension effects, and the possibility of droplet evaporation when the impact surface is hot. Initially, dynamic behavior is examined for isothermal impingement of a droplet moving through air, first without and then with boundary vibration. Isothermal simulations are used to establish how droplet rebound conditions and the time interval between initial contact to detachment vary with droplet diameter for droplet impingement onto a stationary boundary. Heat transfer is then assessed for a liquid droplet initially at saturation temperature passing through steam, followed by contact with a hot vibrating boundary, in which droplet evaporation commences. The paper shows that, for droplet impingement onto a static boundary, the minimum impact velocity for rebound reduces linearly with droplet diameter, whereas the time interval between initial contact and detachment appears to increase linearly with droplet diameter. With the introduction of a vibrating surface, the minimum relative impact velocity for isothermal rebound is found to be higher than the minimum impact velocity for static boundary droplet rebound. For impingement onto a hot surface, in which droplet evaporation commences, it is shown that large-amplitude surface vibration reduces heat transfer, whereas low-amplitude high-frequency vibration appears to increase heat transfer.

The Effect of Nano-Structured Surfaces on Droplet Impingement Heat Transfer

2011 ◽  
Author(s):  
Gary Rosengarten ◽  
Anggito Tetuko ◽  
Ka Kit Li ◽  
Alex Wu ◽  
Robert Lamb
Keyword(s):  
Heat Transfer ◽  
Surface Properties ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Liquid Droplet ◽  
Droplet Impingement ◽  
Cooling Effectiveness ◽  
Structured Surfaces ◽  
The Impact

Droplet impingement is a fundamental process for many applications particularly those involving heat transfer. While there has been considerable work over many years on understanding the flow and heat transfer processes, we have only recently been able to fabricate controllable nanostructured surfaces. Surface structure can have a massive impact on the droplet impact process dynamics and the associated convective heat transfer from the liquid droplet to the surface. In this paper we examine the impact dynamics and heat transfer using simultaneous high speed thermal imaging of the liquid from below, and high speed video camera images from the side for different surfaces, ranging from hydrophilic to superhydrophobic. In this way we characterize the heat transfer process as a function of the droplet dynamics and the surface properties. We show that the heat transfer rate is primarily affected by the contact line dynamics and the wetted area. Due to the superhydrophobic roughness scale being relatively small, the interface resistance offered by the trapped air has only a small effect on the heat transfer rate, and only in the inertia dominated region before maximum spreading diameter. Finally we show that the overall cooling effectiveness of as single impinging droplet is very dependent on the surface properties with hydrophilic surfaces offering the highest cooling effectiveness.

A Study on Evolution of Splat Radius and Temperature in Thermal Spray Process

2018 ◽  
Author(s):  
Manpreet Dash ◽  
Sangharsh Kumar ◽  
Partha Pratim Bandyopadhyay ◽  
Anandaroop Bhattacharya
Keyword(s):  
Heat Transfer ◽  
Thermal Spray ◽  
Molten Metal ◽  
Spray Deposition ◽  
Substrate Surface ◽  
Metal Droplet ◽  
Droplet Impingement ◽  
Impact Process ◽  
The Impact ◽  
Maximum Spreading

The impact process of a molten metal droplet impinging on a solid substrate surface is encountered in several technological applications such as ink-jet printing, spray cooling, coating processes, spray deposition of metal alloys, thermal spray coatings, manufacturing processes and fabrication and in industrial applications concerning thermal spray processes. Deposition of a molten material or metal in form of a droplet on a substrate surface by propelling it towards it forms the core of the spraying process. During the impact process, the molten metal droplet spreads radially and simultaneously starts losing heat due to heat transfer to the substrate surface. The associated heat transfer influences impingement behavior. The physics of droplet impingement is not only related to the fluid dynamics, but also to the respective interfacial properties of solid and liquid. For most applications, maximum spreading diameter of the splat is considered to be an important factor for droplet impingement on solid surfaces. In the present study, we have developed a model for droplet impingement based on energy conservation principle to predict the maximum spreading radius and the radius as a function of time. Further, we have used the radius as a function of time in the heat transfer equations and to study the evolution of splat-temperature and predict the spreading factor and the spreading time and mathematically correlate them to the spraying parameters and material properties.

Effects of Heat Transfer on the Spreading and Freezing of Molten Droplets Impinging Onto Textured Surfaces: A Computational Study

2012 ◽  
Author(s):  
Mehdi Raessi ◽  
Rajkamal Sendha
Keyword(s):  
Heat Transfer ◽  
Impact Velocity ◽  
Computational Study ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Textured Surfaces ◽  
Molten Droplets ◽  
Energy Equations ◽  
The Impact ◽  
Obstacle Height

We present our recent study on spreading and solidification of micro-droplets of alumina impacting onto patterned surfaces textured by micron-size obstacles. We employed an in-house, three-dimensional computational tool that solves the flow and energy equations and takes into account the solidification. We investigated the spreading dynamics, heat transfer, and solidification of the droplets as a function of the height and spacing of the obstacles as well as the impact velocity. The results show that, independent of the obstacle height, the droplet assumes a disk-shape geometry when the obstacles are either packed tightly or are very distanced. The results at intermediate obstacle spacings exhibit the most significant deformations, where the droplet develops long fingers. A quantitative relationship shows the collapse of the final spread diameter of the droplet normalized by the obstacle spacing when plotted against the spacing for different impact velocity as well as the obstacle height.

scholarly journals Analysis of Oil Droplet Deposition Characteristics and Determination of Impact State Criterion in Aero-Engine Bearing Chamber

Processes ◽  
2020 ◽  
Vol 8 (6) ◽  
pp. 741
Author(s):  
Fei Wang ◽  
Lin Wang ◽  
Guoding Chen
Keyword(s):  
Impact Velocity ◽  
Incident Angle ◽  
Droplet Diameter ◽  
Oil Droplets ◽  
Oil Droplet ◽  
Spreading Width ◽  
The Impact ◽  
State Criterion ◽  
Maximum Spreading

The research of oil/air two-phase flow and heat transfer is the fundamental work of the design of lubrication and heat transfer in aero-engine bearing chamber. The determination of impact state criterion of the moving oil droplets with the wall and the analysis of oil droplet deposition characteristics are important components. In this paper, the numerical analysis model of the impact between the moving oil droplet and the wall is established by using the finite volume method, and the simulation of oil droplet impingement on the wall is carried out. Then the effects of oil droplet diameter, impact velocity, and incident angle on the characteristic parameters of impact state are discussed. The characteristic parameters include the maximum spreading length, the maximum spreading width, and the number of splashing oil droplets. Lastly the calculation results are verified through comparing with the experimental results in the literature. The results show as follows: (1) The maximum spreading width of oil droplet firstly increases and then slows down with the incident angle and the oil droplet diameter increasing; (2) when the oil droplet diameter becomes small, the influence of the incident angle on the maximum spreading length of oil droplet is obvious and vice versa; (3) with the impact velocity and diameter of oil droplet increasing, the maximum spreading width of oil droplet increases firstly and then slows down, and the maximum spreading length increased gradually; (4) the number of splashing oil droplets increases with the incident angle and impact velocity increasing; and (5) compared with the experimental data in literature, the critical dimensionless splashing coefficient K c proposed in this paper can better distinguish the impact state of oil droplet.

Droplet Oscillation After Impact on a Solid Surface

2016 ◽  
Author(s):  
Yina Yao ◽  
Shuai Meng ◽  
Cong Li ◽  
Xiantao Chen ◽  
Rui Yang
Keyword(s):  
Contact Angle ◽  
Spray Deposition ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Oscillation Period ◽  
Droplet Spreading ◽  
Oscillation Phenomenon ◽  
The Impact

Droplet spreading and oscillation occur when a liquid droplet impacts on the solid surfaces. This process is vital in many industrial applications, such as ink-jet printing technologies, spray coating and agricultural spray deposition. However, the researches that have been done mainly focused on the spreading process, and less attention has been paid to the droplet oscillation phenomenon, which has influence on the solidification and evaporation process. Therefore, the study on droplet oscillation phenomenon after the impact is necessary and valuable. This paper aims at analyzing the droplet oscillation phenomenon using VOF method. Since the contact angle varies dramatically in the dynamic process, a dynamic contact angle model is introduced to improve the simulation accuracy. The dynamic contact angle model has been verified by comparing the numerical results with experimental and theoretical results. In order to study the factors that may influence the droplet oscillation period, different droplet diameters and impact velocities are utilized in this simulation. The results show that the oscillation period presents a positive relationship with droplet diameter. However, the impact velocity has no apparent influence on the oscillation period, which agrees well with the theoretical analysis.

scholarly journals Why Impacted Yarns Break at Lower Speed Than Classical Theory Predicts

2011 ◽  
Vol 78 (5) ◽  
Author(s):  
James D. Walker ◽  
Sidney Chocron
Keyword(s):  
Impact Velocity ◽  
Classical Theory ◽  
Impact Speed ◽  
Projectile Impact ◽  
Theoretical Maximum ◽  
Theory Result ◽  
Single Yarn ◽  
The Impact ◽  
Good Agreement ◽  
Minimum Impact

Fabrics are an extremely important element of body armors and other armors. Understanding fabrics requires understanding how yarns deform. Classical theory has shown very good agreement with the deformation of a single yarn when impacted transversely. However, the impact speed at which a yarn breaks based on this classical theory is not correct; it has been experimentally noted that yarns break when impacted at a lower speed. This paper explores the mechanism of yarn breakage. The problem of the transverse strike of a yarn by a flat-faced projectile is analytically solved for early times. It is rigorously demonstrated that when a flat-faced projectile strikes a yarn, the minimum impact speed that breaks the yarn will always be at least 11% less than the classical-theory result. It is further shown that when the yarn in front of the projectile “bounces” off the projectile face due to the impact, the impact speed that breaks the yarn is further reduced. If the yarn bounces elastically off the projectile face at twice the impact velocity (the theoretical maximum), there is a 40% reduction in the projectile impact speed that breaks the yarn.

Bubble Formation at Impingement of a Liquid Droplet on a Solid Surface

2000 ◽  
Author(s):  
Hitoshi Fujimoto ◽  
Tomoyuki Ogino ◽  
Osamu Takahashi ◽  
Hirohiko Takuda ◽  
Natsuo Hatta
Keyword(s):  
Solid Surface ◽  
Liquid Droplet ◽  
Droplet Diameter ◽  
Bubble Formation ◽  
Liquid Droplets ◽  
Vapor Bubbles ◽  
Experimental Conditions ◽  
Video Cameras ◽  
The Moment ◽  
The Impact

Abstract The collision of liquid droplets with a solid has been studied experimentally. The time evolution of the liquid/solid contact area as well as the shape of droplets has been observed by means of a flash-photographic method using two video cameras. It has been found that some air between the solid surface and the incoming droplet is entrapped at the moment of impact. In the case where the solid temperature is high (= 450 °C), numerous vapor bubbles appear at the liquid/solid interface after the collision. The bubble formation due to the entrapment of air has been examined for various experimental conditions. Water, and ethanol are used as test liquid. The droplet diameter is 2.4 mm for water and 1.9 mm for ethanol. The impact velocity varies from 0.8 to 3.1 m/s. The entrapment of air has been observed for both liquids under all conditions in the present study.

Heat Transfer During Impact of Elastoplastic and Cohesive Particles

2019 ◽  
Author(s):  
Kuahai Yu ◽  
Danesh Tafti ◽  
Xi Yang ◽  
Shihong Xin
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Impact Velocity ◽  
Room Temperature ◽  
Adhesion Forces ◽  
Time Duration ◽  
Plastic Stage ◽  
Sand Particles ◽  
The Impact ◽  
Impact Duration

Abstract This paper presents a theoretical study of the heat transfer during particles colliding with a surface considering the material elastoplastic properties and adhesion forces of particles. The model divides the impact processes into three stages, the elastic stage, the elastic-plastic stage, and full plastic stage, and assumes that the recovery stage is fully elastic. The rebound velocities of particles are obtained by the comparison of initial kinetic energy and total energy losses, and the major loss mechanisms in the form of adhesion forces and plastic deformation of particles. During each stage of the collision, the impact duration of collision is predicted numerically by integrating the differential equations of contact forces and particle motion. Elastic impact duration and heat transfer of a 4.76 mm stainless steel particle with 304 stainless steel surface agrees well with a previous analytical model. The result shows that at higher impact velocity, a larger percentage of time is spent in the compression stage. Sand particles under 50 μm impacting a nickel based super alloy surface (DD3) from room temperature to 1273 K are evaluated. Time duration decreases with an increase in impact velocity and a decrease in particle size. Heat transfer at particle impact is determined primarily by the contact area and time duration, besides the temperature difference and thermal conductivity. Heat transfer of plastic impact is noticeably smaller than the Sun and Chen’s analytical model, and the difference increases with increase in impact velocity. Adhesion forces affect the time duration significantly at low impact velocity. Heat transfer for 20 μm sand particles at 1073 K, 1173 K and 1273 K is about 1.12, 1.15 and 1.25 times that at room temperature, and about 1.07, 1.08 and 1.15 times the impact duration at room temperature.

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