scholarly journals A Numerical Investigation on the Collision Behavior of Polymer Droplets

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 263 ◽  
Author(s):  
Lijuan Qian ◽  
Hongchuan Cong ◽  
Chenlin Zhu
Keyword(s):  
Surface Tension ◽  
Adaptive Mesh Refinement ◽  
Internal Flow ◽  
Adaptive Mesh ◽  
Flow Region ◽  
Dissipated Energy ◽  
Positive Pressure ◽  
Maximum Deformation ◽  
Droplet Collisions ◽  
Polymer Liquids

Binary droplet collisions are a key mechanism in powder coatings production, as well as in spray combustion, ink-jet printing, and other spray processes. The collision behavior of the droplets using Newtonian and polymer liquids is studied numerically by the coupled level-set and volume of fluid (CLSVOF) method and adaptive mesh refinement (AMR). The deformation process, the internal flow fields, and the energy evolution of the droplets are discussed in detail. For binary polymer droplet collisions, compared with the Newtonian liquid, the maximum deformation is promoted. Due to the increased viscous dissipation, the colliding droplets coalesce more slowly. The stagnant flow region in the velocity field increases and the flow re-direction phenomenon is suppressed, so the polymer droplets coalesce permanently. As the surface tension of the polymer droplets decreases, the kinetic and the dissipated energy increases. The maximum deformation is promoted, and the coalescence speed of the droplets slows down. During the collision process, the dominant pressure inside the polymer droplets varies from positive pressure to negative pressure and then to positive pressure. At low surface tension, due to the non-synchronization in the movement of the interface front, the pressure is not smooth and distributes asymmetrically near the center of the droplets.

scholarly journals A Numerical Investigation on the Collision Behavior of Unequal-Sized Micro-Nano Droplets

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1746
Author(s):  
Lijuan Qian ◽  
Jingqi Liu ◽  
Hongchuan Cong ◽  
Fang Zhou ◽  
Fubing Bao
Keyword(s):  
Initial Velocity ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Size Ratio ◽  
Large Droplet ◽  
Collision Dynamics ◽  
Spreading Effect ◽  
Droplet Collisions ◽  
Filament Structure ◽  
Energy Converting

Micro-nano droplet collisions are fundamental phenomena in the applications of nanocoating, nano spray, and microfluidics. Detailed investigations of the process of the droplet collisions under higher Weber are still lacking when compared with previous research studies under a low Weber number below 120. Collision dynamics of unequal-sized micro-nano droplets are simulated by a coupled level-set and volume of fluid (CLSVOF) method with adaptive mesh refinement (AMR). The effects of the size ratio (from 0.25 to 0.75) and different initial collision velocities on the head-on collision process of two unequal-sized droplets at We = 210 are studied. Complex droplets will form the filament structure and break up with satellite droplets under higher Weber. The filament structure is easier to disengage from the complex droplet as the size ratio increases. The surface energy converting from kinetic energy increases with the size ratio, which promotes a better spreading effect. When two droplets keep the constant relative velocity, the motion tendency of the droplets after the collision is mainly dominated by the large droplet. On one hand, compared with binary equal-sized droplet collisions, a hole-like structure can be observed more clearly since the initial velocity of a large droplet decreases in the deformation process of binary unequal-sized droplets. On the other hand, the rim spreads outward as the initial velocity of the larger droplet increases, which leads to its thickening.

Pattern Formation in Directional Solidification

2003 ◽  
Vol 782 ◽  
Author(s):  
Mike Greenwood ◽  
Mikko Haataja ◽  
Nikolas Provatas
Keyword(s):  
Surface Tension ◽  
Directional Solidification ◽  
Thermal Gradient ◽  
Adaptive Mesh Refinement ◽  
Interface Velocity ◽  
Adaptive Mesh ◽  
Field Method ◽  
Phase Field Method ◽  
Dendrite Morphology ◽  
Small Surface

We simulate directional solidification using the phase field method solved with adaptive mesh refinement. We examine length scale selection for two cases. For small surface tension anisotropy directed at forty five degrees relative to the pulling direction, we observe a transition from a seaweed to dendrite morphology as the thermal gradient is lowered, consistent with recent experimental findings. We show that the morphology of crystal structures can be unambiguously characterized through the local interface velocity distribution. We derive semi-empirically a phase diagram for the transition from seaweed to dendrites as a function of thermal gradient and pulling speed. As surface tension anisotropy is increased and aligned with the pulling direction we observe cellular and dendritic arrays directed in the pulling direction. We characterize wavelength selection and obtain a new universal scaling of the wavelength that differs from previous theories.

Dynamics of internal jets in the merging of two droplets of unequal sizes

2016 ◽  
Vol 795 ◽  
pp. 671-689 ◽  
Author(s):  
Chenglong Tang ◽  
Jiaquan Zhao ◽  
Peng Zhang ◽  
Chung K. Law ◽  
Zuohua Huang
Keyword(s):  
Surface Tension ◽  
Weber Number ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Volume Of Fluid Method ◽  
Internal Mixing ◽  
Mixing Dynamics ◽  
Mixing Patterns ◽  
The Impact ◽  
Refinement Algorithm

The head-on collision, merging and internal mixing dynamics of two unequal-sized droplets were experimentally studied and interpreted, using water, $n$-decane and $n$-tetradecane to identify the distinguishing effects of surface tension and liquid viscosity on the merging and mixing patterns. It is shown that, upon merging of water and $n$-decane droplets, mushroom-like jets of dissimilar characteristics develop within the merged mass for small and large values of the impact Weber number (We), and that such jets are not developed for intermediate values of We. Furthermore, such jet-like mixing patterns were not observed for droplets of $n$-tetradecane, which has smaller surface tension and larger viscosity as compared to water. A regime nomogram relating the Ohnesorge and symmetric Weber numbers is constructed, providing a unified interpretation of the internal mixing patterns. Numerical simulations based on an improved volume-of-fluid method and an adaptive mesh refinement algorithm provide auxiliary diagnoses of the flow fields and the observed phenomena.

Dynamic structural analysis of connecting rod through adaptive mesh refinement for different materials

2018 ◽  
Vol 50 (04) ◽  
pp. 561-570
Author(s):  
I. A. QAZI ◽  
A. F. ABBASI ◽  
M. S. JAMALI ◽  
INTIZAR INTIZAR ◽  
A. TUNIO ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Connecting Rod ◽  
Dynamic Structural Analysis

scholarly journals Insights into the physics when modelling cold gas clouds in a hot plasma

2019 ◽  
Vol 490 (1) ◽  
pp. L52-L56
Author(s):  
Bastian Sander ◽  
Gerhard Hensler
Keyword(s):  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Careful Consideration ◽  
Necessary Condition ◽  
Interstellar Clouds ◽  
Hot Plasma ◽  
Magnetic Dipole Field ◽  
Set Up ◽  
Self Gravity ◽  
Cold Gas

ABSTRACT This paper aims at studying the reliability of a few frequently raised, but not proven, arguments for the modelling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modellers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial set-up as homogeneous. We apply the adaptive-mesh refinement code flash with extensions to metal-dependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules, and ionization of atoms. We show that the criterion of Jeans mass or Bonnor–Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical time-scales. The second part of this paper is dedicated to analytically study the reduction of heat conduction by a magnetic dipole field. We demonstrate that in this configuration, the effective heat flow, i.e. integrated over the cloud surface, is suppressed by only 32 per cent by magnetic fields in energy equipartition and still insignificantly for even higher field strengths.

Sign in / Sign up

Export Citation Format

Share Document