scholarly journals We -T classification of diesel fuel droplet impact regimes

2018 ◽  
Vol 474 (2215) ◽  
pp. 20170759 ◽  
Author(s):  
Hesamaldin Jadidbonab ◽  
Ilias Malgarinos ◽  
Ioannis Karathanassis ◽  
Nicholas Mitroglou ◽  
Manolis Gavaises
Keyword(s):  
Surface Temperature ◽  
High Speed ◽  
Ambient Pressure ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
High Speed Imaging ◽  
Two Phase ◽  
Post Impact ◽  
T Classification ◽  
The Impact

A combined experimental and computational investigation of micrometric diesel droplets impacting on a heated aluminium substrate is presented. Dual view high-speed imaging has been employed to visualize the evolution of the impact process at various conditions. The parameters investigated include wall-surface temperature ranging from 140 to 400°C, impact Weber and Reynolds numbers of 19–490 and 141–827, respectively, and ambient pressure of 1 and 2 bar. Six possible post-impact regimes were identified, termed as Stick, Splash, Partial-Rebound, Rebound, Breakup-Rebound and Breakup-Stick , and plotted on the We-T map. Additionally, the temporal variation of the apparent dynamic contact angle and spreading factor have been determined as a function of the impact Weber number and surface temperature. Numerical simulations have also been performed using a two-phase flow model with interface capturing, phase-change and variable physical properties. Increased surface temperature resulted to increased maximum spreading diameter and induced quicker and stronger recoiling behaviour, mostly attributed to the change of liquid viscosity.

scholarly journals The Effect of Surface Roughness on the Contact Line and Splashing Dynamics of Impacting Droplets

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Miguel A. Quetzeri-Santiago ◽  
Alfonso A. Castrejón-Pita ◽  
J. Rafael Castrejón-Pita
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
High Speed ◽  
Dynamic Contact Angle ◽  
Past Research ◽  
Dynamic Contact ◽  
Substrate Roughness ◽  
High Speed Imaging ◽  
Mean Width ◽  
Fluid Properties

Abstract Whether a droplet splashes upon impact onto a solid is known to depend not only on the fluid properties and its speed, but also on the substrate characteristics. Past research has shown that splashing is heavily influenced by the substrate roughness. Indeed, in this manuscript, we demonstrate that splashing is ruled by the surface roughness, the splashing ratio, and the dynamic contact angle. Experiments consist of water and ethanol droplets impacting onto solid substrates with varying degrees of roughness. High speed imaging is used to extract the dynamic contact angle as a function of the spreading speed for these impacting droplets. During the spreading phase, the dynamic contact angle achieves an asymptotic maximum value, which depends on the substrate roughness and the liquid properties. We found that this maximum dynamic contact angle, together with the liquid properties, the ratio of the peak to peak roughness and the surface feature mean width, determines the splashing to no-splashing threshold. In addition, these parameters consistently differentiate the splashing behaviour of impacts onto smooth hydrophilic, hydrophobic and superhydrophobic surfaces.

scholarly journals Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 208
Author(s):  
Peter Reinke ◽  
Jan Ahlrichs ◽  
Tom Beckmann ◽  
Marcus Schmidt
Keyword(s):  
Shear Flow ◽  
Pressure Gradient ◽  
High Speed ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Two Phase ◽  
Bubble Generation ◽  
Gap Flow ◽  
The Impact

The volume-of-flow method combined with the Rayleigh–Plesset equation is well established for the computation of cavitation, i.e., the generation and transportation of vapor bubbles inside a liquid flow resulting in cloud, sheet or streamline cavitation. There are, however, limitations, if this method is applied to a restricted flow between two adjacent walls and the bubbles’ size is of the same magnitude as that of the clearance between the walls. This work presents experimental and numerical results of the bubble generation and its transportation in a Couette-type flow under the influence of shear and a strong pressure gradient which are typical for journal bearings or hydraulic seals. Under the impact of variations of the film thickness, the VoF method produces reliable results if bubble diameters are less than half the clearance between the walls. For larger bubbles, the wall contact becomes significant and the bubbles adopt an elliptical shape forced by the shear flow and under the influence of a strong pressure gradient. Moreover, transient changes in the pressure result in transient cavitation, which is captured by high-speed imaging providing material to evaluate transient, three-dimensional computations of a two-phase flow.

A rebounding droplet impacting on a static droplet

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Joo Hyun Moon ◽  
Jeffrey S. Allen ◽  
Seong Hyuk Lee
Keyword(s):  
Impact Velocity ◽  
High Speed ◽  
Dynamic Contact Angle ◽  
Free Fall ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Gap Formation ◽  
Spherical Cap ◽  
Number Range ◽  
The Impact

This study aims to experimentally examine rebounding characteristics of a free-fall droplet which impacts on a static droplet with a spherical-cap shape in a low Weber number range. Two well-aligned high-speed cameras were used for visualization of droplet behaviors after impact. From the image analysis, the influence of impact velocity, offset distance and static droplet volume on the rebound characteristics was examined. The results show that the dynamic contact angle and the contact diameter of a static droplet change significantly with time after impact. In particular, a substantial change in dynamic contact angles for different offset distances is also observed. Contact diameters are also varied larger with the increase in the impact velocity. It is thought that occurrence of droplet rebound may be because of air-gap formation at the interface inhibiting viscous film drainage, coming from droplet oscillation before impact.

A Numerical Analysis on the Correlation Between Impact Conditions of Blood Drop on the Wall and its Resulting Bloodstain Pattern

2014 ◽  
Author(s):  
Geonkang Lee ◽  
Nahmkeon Hur ◽  
Young-Il Seo
Keyword(s):  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Crime Scene ◽  
Impact Angle ◽  
Fluid Viscosity ◽  
Interfacial Flows ◽  
Two Phase ◽  
Bloodstain Pattern ◽  
The Impact ◽  
Important Evidence

At the crime scene in case of homicide, spattered bloodstains at the incident site are important evidence. The patterns of the bloodstain on the floors and walls are determined by the impact conditions of blood drop such as drop size, impact angle and velocity. By analyzing the bloodstain pattern, one can retrace the origin of blood drops to reconstruct the crime scene. In the present study, motions of blood drop are analyzed to figure out the correlation between impact conditions of blood drop and bloodstain patterns. Two phase interfacial flows of blood drop impacting the wall are numerically simulated with the VOF method. To get the accurate results of bloodstains on the wall, non-Newtonian fluid viscosity and dynamic contact angle are used as the blood properties. By using these methods, patterns of bloodstains created from the blood drop are predicted for various Reynolds and Weber numbers.

scholarly journals Air mediates the impact of a compliant hemisphere on a rigid smooth surface

Soft Matter ◽  
2021 ◽  
Author(s):  
Siqi Zheng ◽  
Sam Dillavou ◽  
John M. Kolinski
Keyword(s):  
Elastic Body ◽  
Elastic Properties ◽  
Impact Velocity ◽  
Solid Surface ◽  
High Speed ◽  
Smooth Surface ◽  
High Speed Imaging ◽  
The Impact ◽  
Rigid Smooth

When a soft elastic body impacts upon a smooth solid surface, the intervening air fails to drain, deforming the impactor. High-speed imaging with the VFT reveal rich dynamics and sensitivity to the impactor's elastic properties and the impact velocity.

Effect of Pressure on Bubble Growth Within Liquid Droplets at the Superheat Limit

1982 ◽  
Vol 104 (4) ◽  
pp. 750-757 ◽  
Author(s):  
C. T. Avedisian
Keyword(s):  
Vapor Bubble ◽  
Bubble Growth ◽  
High Speed ◽  
Ambient Pressure ◽  
Organic Liquid ◽  
Liquid Droplets ◽  
Growth Data ◽  
Two Phase ◽  
Photographic Evidence ◽  
Good Agreement

A study of high-pressure bubble growth within liquid droplets heated to their limits of superheat is reported. Droplets of an organic liquid (n-octane) were heated in an immiscible nonvolatile field liquid (glycerine) until they began to boil. High-speed cine photography was used for recording the qualitative aspects of boiling intensity and for obtaining some basic bubble growth data which have not been previously reported. The intensity of droplet boiling was found to be strongly dependent on ambient pressure. At atmospheric pressure the droplets boiled in a comparatively violent manner. At higher pressures photographic evidence revealed a two-phase droplet configuration consisting of an expanding vapor bubble beneath which was suspended a pool of the vaporizing liquid. A qualitative theory for growth of the two-phase droplet was based on assuming that heat for vaporizing the volatile liquid was transferred across a thin thermal boundary layer surrounding the vapor bubble. Measured droplet radii were found to be in relatively good agreement with predicted radii.

scholarly journals Propellant Combustion Wave Studies by Embedded Thermocouple and Imaging Method at Ambient Pressure

2020 ◽  
Author(s):  
Rakesh Kumar Kalal ◽  
Himanshu Shekhar ◽  
Prashant Sudhir Alegaonkar ◽  
Shrikant Pande
Keyword(s):  
Surface Temperature ◽  
High Speed ◽  
Ambient Pressure ◽  
Combustion Mechanism ◽  
Imaging Method ◽  
Flame Zone ◽  
Sem Images ◽  
Propellant Combustion ◽  
Double Base ◽  
Zone Temperature

This paper discusses the method for propellant combustion studies with embedded thermocouple and imaging method at ambient pressure. In this study, three different propellant compositions are experimentally evaluated for surface temperature, flame zone temperature with embedded thermocouple, and reaction zone thickness with high-speed imaging of propellant during combustion at ambient pressure. Preheat zone and flame zone temperature profiles are recorded with time and surface temperature is determined with available models. Observation of these experiments gives the difference between combustion mechanism of double-base propellant with diethylene glycol dinitrate (DEGDN) and 2,4-dinitrotoluene (DNT), composite propellant (CP) and CP with energetic binder. Scanning electron microscope (SEM) images analysis for pristine and quenched sample is also presented.

Numerical Study of a Small Droplet Movement in a Microchannel under Heat Source

2019 ◽  
Vol 894 ◽  
pp. 104-111
Author(s):  
Thanh Long Le ◽  
Jyh Chen Chen ◽  
Huy Bich Nguyen
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Numerical Study ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Initial Position ◽  
Immiscible Fluids ◽  
Two Phase

In this study, the numerical computation is used to investigate the transient movement of a water droplet in a microchannel. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be an ambient temperature. 40mW heat source is placed at the distance of 1 mm from the initial position of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly, and then decreases continuously. The dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during actuation process.

Impingement of an unsteady two-phase jet on unheated and heated flat plates

1993 ◽  
Vol 252 ◽  
pp. 499-523 ◽  
Author(s):  
İ. Bedii Özdemir ◽  
J. H. Whitelaw
Keyword(s):  
Wall Temperature ◽  
High Speed ◽  
Continuous Phase ◽  
Size Class ◽  
Wall Jet ◽  
Flat Plates ◽  
Two Phase ◽  
Secondary Atomization ◽  
Wall Jet Flow ◽  
The Impact

This paper is concerned with an experimental investigation of the oblique impingement of an unsteady, axisymmetric two-phase jet on heated surfaces. Size and velocity were measured simultaneously with a phase-Doppler velocimeter, and the spatial distributions over the wall jet were found to be correlated with the interfacial activities as inferred from vertical velocity measurements in the vicinity of the wall. These results are discussed together with size measurements by a laser-diffraction technique to quantify the effect of the approach conditions of the inflowing jet droplet field and wall temperature in relation to mechanisms of secondary atomization.Two mechanisms of secondary atomization were identified; the first did not involve direct wall contact and was due to the strain acting on the droplets by the continuous phase within the impingement region and was enhanced by thermal effects from the wall to cause breakup. The approaching velocity of the inflowing droplets to the plate was important to this process so that higher velocities increased the rate of strain within the impingement region and, consequently, the wall temperature promoting the secondary atomization shifted towards lower values. The second mechanism required direct wall contact and involved atomization of the film deposited on the wall by the impingement of the inflowing two-phase jet. With the penetration of high-speed inflowing droplets into the film, liquid mass was raised into the two-phase medium due to splashes from the film so that a new size class with larger droplets was generated. The resulting large droplets tended to stay close to the wall within the impingement region with small vertical velocitiesIn between the injections, the suspended droplet field above the film oscillated normal to the plate as a cloud so that the impact of large droplets on the film resulted in coalescence with the film and the ejection of smaller numbers of small droplets. The unsteady wall jet flow, caused by the arrival of the spray at the plate, swept the vertically oscillating droplet cloud radially outwards so that the resulting radial transport caused the dynamics of the unsteady film to be correlated with the size characteristics of the unsteady wall jet. Based on this phenomenological description, a radial droplet transport equation is derived.The correlation suggests that the secondary atomization with direct wall contact is the dominant process for the generation of a new size class within the wall flow and initiates the mutual interaction between the unsteady film and wall jet droplet field.

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