scholarly journals Pressure generated at the instant of impact between a liquid droplet and solid surface

2018 ◽  
Vol 5 (12) ◽  
pp. 181101 ◽  
Author(s):  
Y. Tatekura ◽  
M. Watanabe ◽  
K. Kobayashi ◽  
T. Sanada
Keyword(s):  
Solid Surface ◽  
Shape Factor ◽  
Liquid Droplet ◽  
Pressure Rise ◽  
Propagation Speed ◽  
Spherical Shape ◽  
Water Hammer ◽  
Droplet Impact ◽  
Maximum Pressure ◽  
The Impact

The prime objective of this study is to answer the question: How large is the pressure developed at the instant of a spherical liquid droplet impact on a solid surface? Engel first proposed that the maximum pressure rise generated by a spherical liquid droplet impact on a solid surface is different from the one-dimensional water-hammer pressure by a spherical shape factor (Engel 1955 J. Res. Natl Bur. Stand. 55 (5), 281–298). Many researchers have since proposed various factors to accurately predict the maximum pressure rise. We numerically found that the maximum pressure rise can be predicted by the combination of water-hammer theory and the shock relation; then, we analytically extended Engel’s elastic impact model, by realizing that the progression speed of the contact between the gas–liquid interface and the solid surface is much faster than the compression wavefront propagation speed at the instant of the impact. We successfully correct Engel’s theory so that it can accurately provide the maximum pressure rise at the instant of impact between a spherical liquid droplet and solid surface, that is, no shape factor appears in the theory.

Effect of Materials’ Wettability on the Dynamic Behavior of Droplet Impact onto a Rough Solid Surface

2011 ◽  
Vol 320 ◽  
pp. 341-346
Author(s):  
Jing Cui ◽  
Yang Liu ◽  
Wei Zhong Li ◽  
Ning Zhang
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Liquid Droplet ◽  
Droplet Impact ◽  
Apparent Contact Angle ◽  
Bottom Surface ◽  
Roughness Elements ◽  
Hydrophilic Material ◽  
Boltzmann Method ◽  
Intrinsic Contact Angle

In this paper, the effect of material’s wettability on the droplet impact has been investigated by numerical apporach. The unsteady flow behaviors of liquid droplet impacting against the rough solid surface with different wettabilities have been simulated based on lattice Boltzmann method. The spreading and bounding characterisitcs of droplet have been discussed. For the hydrophilic material, the droplet will sink into the grooves among roughness bumps, and its apparent contact angle in steady stead will be smaller than its corresponding intrinsic contact angle; while for the hydrophilic material, droplet will flow into the grooves but suspend on the top of roughness elements without any contacting with the bottom surface, and the apparent contact angle is larger than its intrinsic contact angle.

The mechanism of a splash on a dry solid surface

2011 ◽  
Vol 690 ◽  
pp. 148-172 ◽  
Author(s):  
Shreyas Mandre ◽  
Michael P. Brenner
Keyword(s):  
Solid Surface ◽  
High Speed ◽  
Liquid Droplet ◽  
Contact Point ◽  
Quantitative Agreement ◽  
Gas Pressure ◽  
Liquid Viscosity ◽  
Ink Jet ◽  
Jet Printing ◽  
The Impact

AbstractFrom rain storms to ink jet printing, it is ubiquitous that a high-speed liquid droplet creates a splash when it impacts on a dry solid surface. Yet, the fluid mechanical mechanism causing this splash is unknown. About fifty years ago it was discovered that corona splashes are preceded by the ejection of a thin fluid sheet very near the vicinity of the contact point. Here we present a first-principles description of the mechanism for sheet formation, the initial stages of which occur before the droplet physically contacts the surface. We predict precisely when sheet formation occurs on a smooth surface as a function of experimental parameters, along with conditions on the roughness and other parameters for the validity of the predictions. The process of sheet formation provides a semi-quantitative framework for studying the subsequent events and the influence of liquid viscosity, gas pressure and surface roughness. The conclusions derived from this framework are in quantitative agreement with previous measurements of the splash threshold as a function of impact parameters (the size and velocity of the droplet) and in qualitative agreement with the dependence on physical properties (liquid viscosity, surface tension, ambient gas pressure, etc.) Our analysis predicts an as yet unobserved series of events within micrometres of the impact point and microseconds of the splash.

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.

Effect of multi-valve closure on superposed pressure in a tree-type long distance gravitational water supply system

2019 ◽  
Vol 68 (6) ◽  
pp. 420-430
Author(s):  
Xingtao Wang ◽  
Jian Zhang ◽  
Xiaodong Yu ◽  
Sheng Chen ◽  
Wenlong Zhao ◽  
...  
Keyword(s):  
Water Supply ◽  
Pressure Rise ◽  
Water Hammer ◽  
Supply System ◽  
Water Supply System ◽  
Maximum Pressure ◽  
Valve Closure ◽  
Long Distance ◽  
Maximum Water ◽  
Tree Type

Abstract Valves are installed at the end of each branch pipeline in a tree-type long distance gravitational water supply system to regulate flow. However, the sequential closing of all valves may cause a tremendous superposed pressure rise, even larger than the pressure rise under simultaneous valve closure. In this paper, the effects of sequential valve closure on the superposed maximum water hammer pressure rise in a pipeline were investigated. By using the wave superposition principle, a sequential valve closure formula leading to maximum water hammer was proposed and verified using numerical simulation based on a practical project. In addition, the superposed maximum pressure rises in the pipeline were compared under single, simultaneous and sequential valve closure, respectively. The results show that the sequential valve closure formula agrees well with the numerical results and the pressure rise in the pipeline under the sequential closing was the largest. Moreover, compared with the superposed maximum pressure rises at the main pipeline, the effect of sequential valve closure on superposed maximum pressure rise at the branch pipeline is more sensitive.

scholarly journals Influence of acetylene on methane–air explosion characteristics in a confined chamber

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jinzhang Jia ◽  
Jinchao Zhu ◽  
Wenxing Niu ◽  
Jing Zhang
Keyword(s):  
Free Radicals ◽  
Volume Fraction ◽  
Pressure Rise ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Maximum Pressure ◽  
Mixed Gas ◽  
Explosion Pressure ◽  
Combustion Modes ◽  
The Impact

AbstractTo study the impact of acetylene on methane explosions, the safe operation of coal mines should be ensured. In this paper, a 20 L spherical tank was used to study the explosive characteristics of acetylene–methane–air mixture. In addition, the GRI-Mech3.0 mechanism was used to study the chemical kinetic mechanism for the mixed gas, and the effect of adding acetylene on the sensitivity of methane and the yield of free radicals was analysed. The results show that acetylene can expand the scope for methane explosion, lower the lower explosion limit, and increase the risk of explosion. Acetylene increases the maximum explosion pressure, laminar combustion rate and maximum pressure rise rate for the methane–air mixture while shortening the combustion time. Three combustion modes for the acetylene–methane–air mixture were determined: methane-dominated, transitional and acetylene-dominated combustion modes. Chemical kinetic analysis for the mixed gas shows that as the volume fraction of acetylene increases, the generation rate for key free radicals (H*, O* and OH*) gradually increases, thereby increasing the intensity of the explosive reaction. The results from this research will help formulate measures to prevent coal mine explosion accidents.

Events before droplet splashing on a solid surface

2010 ◽  
Vol 647 ◽  
pp. 163-185 ◽  
Author(s):  
MADHAV MANI ◽  
SHREYAS MANDRE ◽  
MICHAEL P. BRENNER
Keyword(s):  
Surface Tension ◽  
Solid Surface ◽  
Liquid Droplet ◽  
Thin Sheet ◽  
Initial Contact ◽  
Viscous Forces ◽  
Self Similar Solution ◽  
Self Similar ◽  
Physical Effects ◽  
The Impact

A high-velocity (≈1 ms−1) impact between a liquid droplet (≈1 mm) and a solid surface produces a splash. Classical observations traced the origin of this splash to a thin sheet of fluid ejected near the impact point, though the fluid mechanical mechanism leading to the sheet is not known. Mechanisms of sheet formation have heretofore relied on initial contact of the droplet and the surface. In this paper, we theoretically and numerically study the events within the time scale of about 1 μs over which the coupled dynamics between the gas and the droplet becomes important. The droplet initially tries to contact the substrate by either draining gas out of a thin layer or compressing it, with the local behaviour described by a self-similar solution of the governing equations. This similarity solution is not asymptotically consistent: forces that were initially negligible become relevant and dramatically change the behaviour. Depending on the radius and impact velocity of the droplet, we show that the solution is overtaken by initially subdominant physical effects such as the surface tension of the liquid–gas interface or viscous forces in the liquid. At low impact velocities surface tension stops the droplet from impacting the surface, whereas at higher velocities viscous forces become important before surface tension. The ultimate dynamics of the interface once droplet viscosity cannot be neglected is not yet known.

scholarly journals VALVE SELECTION FOR THE PURPOSE OF REDUCING THE WATER HAMMER EFFECT IN A PRESSURIZED PIPELINE

2019 ◽  
pp. 217
Author(s):  
Milica Nikodijevic ◽  
Živojin Stamenković ◽  
Jelena Petrović ◽  
Miloš Kocić
Keyword(s):  
Hydraulic System ◽  
Pressure Rise ◽  
Control Valve ◽  
Water Hammer ◽  
Maximum Pressure ◽  
Transient Regimes ◽  
Butterfly Needle ◽  
Efficient Protection ◽  
Selection For ◽  
Water Hammer Effect

This paper discusses the gravity-fed hydraulic system, which consists of the upper reservoir, the lower reservoir, the pipeline, and valves. To achieve simpler and more efficient protection of a system against water hammer, it is advisable to establish conditions in which the pressure rises as little as possible during transient regimes without using any protective equipment. The discussion focuses on the pressure rise caused by different valve types: butterfly, needle, and ball valves, as well as two valve closure intervals – 20 and 40 seconds. The systems considered have nominal diameters of DN 300 and DN 600. The problem was studied using a simulation of unsteady flow regimes of hydraulic transport. The obtained results regarding the maximum pressure rise due to water hammer were used to select the most satisfactory control valve for the considered hydraulic system.

Order Estimation of Physical Processes in Dynamics of Steam-Water Mixed Spray Cleaning Technique

2012 ◽  
Vol 187 ◽  
pp. 141-144
Author(s):  
Masao Watanabe ◽  
Toshiyuki Sanada ◽  
Takashi Mashiko ◽  
Atsushi Hayashida
Keyword(s):  
Impact Velocity ◽  
Solid Surface ◽  
Liquid Droplet ◽  
Viscous Force ◽  
Vapor Flow ◽  
Physical Processes ◽  
Physical Force ◽  
Order Estimation ◽  
Study Results ◽  
The Impact

We have been developing an innovative ultra-low environmental load cleaning technique by the use of steam-water mixed spray. We showed that this technique is quite effective in both cleaning and photo-resist stripping. We also found that the physical force associated with steam-water mixed spray is greater than that with air-water mixed spray; hence we proposed that the condensation plays an important role in this cleaning technique. In order to discuss further this mechanism, we perform the order estimation of physical processes in dynamics of liquid droplet moving in vapor flow impacting on a solid interface in this study. Results show that droplet impact velocity can be reduced while the droplet approaches to the solid surface. However, the vapor in the gap can condensate to either the liquid droplet or the solid surface with the velocity whose order of magnitude cannot be negligible compared to the impact velocity; hence the amount of vapor that should be pushed out from gap can be drastically reduced, This condensation results in the significant reduction of viscous force. This reduction of force with the existence of condensation reduces the impact velocity deceleration. Consequently significantly large impact pressure is generated.

Hydrodynamic Phenomena During High-Speed Collision Between Liquid Droplet and Rigid Plane

1973 ◽  
Vol 95 (2) ◽  
pp. 276-292 ◽  
Author(s):  
Yen C. Huang ◽  
F. G. Hammitt ◽  
W-J Yang
Keyword(s):  
High Speed ◽  
Liquid Droplet ◽  
Lateral Flow ◽  
Maximum Pressure ◽  
Two Dimensional ◽  
Droplet Shape ◽  
One Dimensional ◽  
Liquid Impact ◽  
The Impact ◽  
Impact Problem

The dynamics of high-speed impact between a compressible water droplet and a rigid solid surface is investigated analytically. The purpose of the study is to examine the mechanism leading to the erosion of a material due to liquid impingement. A Compressible-Cell-and-Marker (ComCAM) numerical method is developed to solve the differential equations governing the unsteady, two-dimensional liquid-solid impact phenomena. The method is designed to solve this unsteady portion up until the flow reasonably approaches the steady-state solution. The validity of the method is confirmed by comparing its numerical results with the idealized exact solution for the classical one-dimensional liquid impact problem. The accuracy of the numerical reresults is found to be very good in that only slight numerical oscillations occur. Viscosity and surface tension are neglected as seems resaonable with the relatively large drops and high velocities considered. Pressure and velocity distributions are solved as a function of time. The deformation of a drop is also recorded for three different shapes: cylindrical, spherical, and a combination of the two, which may more closely model the actual droplet shapes to be encountered in such impacts. Typical liquid impact Mach numbers of 0.2 and 0.5 (sonic velocity referred to water) were studied. Thus impact velocities of about 980 and 2450 fps are considered. Compression predominates during the early stages of the impact, while rarefaction governs later, during which time the radial lateral flow velocity exceeds the initial impact velocity. The reflection of compression waves and the lateral flow leads to the possibility of cavitation within the drop, due to the consequent generation of negative pressures, exists. The maximum pressure calculated in this two-dimensional liquid impact problem is found to be less than the one-dimensional maximum pressure for all three different droplets in various degrees. It is found that droplet shape impact angle and liquid impact Mach number are the only important parameters of the problem for a flat fully-rigid target surface. As more time elapses, i.e., up to 2–3 μsec for a 2.0 mm-dia drop, the maximum pressure shifts from the center of the contact area radially outward, while the pressure at the center attenuates rapidly toward conventional stagnation pressure.

Numerical Investigation of Water Droplet Impact on Solid Surface in Microgravity

2013 ◽  
Vol 390 ◽  
pp. 65-70
Author(s):  
Jun Jun Tao ◽  
Jun Qin ◽  
Xue Han ◽  
Yong Ming Zhang
Keyword(s):  
Solid Surface ◽  
Water Droplet ◽  
Normal Gravity ◽  
Numerical Study ◽  
Liquid Droplet ◽  
Water Mist ◽  
Droplet Impact ◽  
Gravity Level ◽  
Vof Model ◽  
Fuel Vapour

A numerical study based on VOF model has been carried out to investigate the dynamics of water droplet impact on solid surface in microgravity in comparison with that in normal gravity to discuss the differences of the extinguishing mechanism of water mist in different gravity level. Water droplets with different initial diameters and impact velocities were considered. The simulated results show that the deformation process in microgravity lags behind that in normal gravity. And it was also found that Dmaxand spread velocities are smaller in microgravity as the potential energy decreases and the time taken for a liquid droplet to reach its maximum spread has no obvious regularity. Hence, the effect of cooling the fuel surface and diluting fuel vapour with water mist in microgravity may be not as good as that in normal gravity.The critical impact Weber number for water droplet breaking up in microgravity is lower than that in normal gravity as the reduction of the value of Bond number, which may result in diluting fuel vapour with water mist in microgravity being more effective than that in normal gravity in some case.

Sign in / Sign up

Export Citation Format

Share Document