The effect of unidirectional shear flow-induced orientation on foaming properties of polypropylene

2020 ◽  
Vol 40 (3) ◽  
pp. 193-202
Author(s):  
Yun Zhang ◽  
Chunling Xin ◽  
Yanbin Su ◽  
Yadong He
Keyword(s):  
Crystal Structure ◽  
Flow Direction ◽  
Amorphous Ribbon ◽  
Subsurface Layer ◽  
Nucleation And Growth ◽  
Expansion Ratio ◽  
Bubble Nucleation ◽  
Process Conditions ◽  
Foaming Properties ◽  
Degree Of Orientation

AbstractWhen the semi-crystalline polymers undergo shearing during flow, the orientation of the molecular chains are induced. In order to study the effect of polypropylene orientation on foaming, we designed an injection mold with a long flow ratio. The samples were prepared by different process conditions and characterized by polarized Fourier transform infrared spectroscopy (FTIR). The degree of orientation was calculated by infrared dichroism. It was found that the orientation of the amorphous region has the greatest influence, and the subsurface layer in the cross section along the flow direction had the largest degree of orientation. The samples were foaming in a self-made sealed cavity under the same condition. The foamed samples were observed by scanning electron microscopy, and it was found that the shish-kebab crystal structure was induced in the surface layer and the subsurface layer under strong shear force. The shish-kebab crystal structure restricted the space for bubble nucleation and growth, and a large number of sub-micron and nano-scale cells appeared in the space of nucleation and growth. Along the flow orientation direction, the longitudinal and transverse sections of each foamed sample with the degree of orientation decreases, the density of cells and the average diameter of cells increases gradually, and the expansion of the foams have an advantage in the direction of flow orientation. The degree of orientation corresponding to the amorphous ribbon (1153 cm−1) of all the samples were arranged from small to large, and it was found that the expansion ratio decreased when the degree of orientation increased. The effect of orientation on foaming properties of polypropylene provides a new strategy for designing other polymer foams.

Crystal structure images of large gold clusters and growing crystals by HRTEM

1984 ◽  
Vol 42 ◽  
pp. 428-429
Author(s):  
L.R. Wallenberg ◽  
J.-O. Bovin ◽  
G. Schmid
Keyword(s):  
Crystal Structure ◽  
Nucleation And Growth ◽  
Close Packing ◽  
Gold Clusters ◽  
Molecular Weight Determination ◽  
Growth Mechanisms ◽  
Starting Point ◽  
Different Types ◽  
Nucleation And Growth Mechanisms ◽  
Points Of View

Metallic clusters are interesting from various points of view, e.g. as a mean of spreading expensive catalysts on a support, or following heterogeneous and homogeneous catalytic events. It is also possible to study nucleation and growth mechanisms for crystals with the cluster as known starting point.Gold-clusters containing 55 atoms were manufactured by reducing (C6H5)3PAuCl with B2H6 in benzene. The chemical composition was found to be Au9.2[P(C6H5)3]2Cl. Molecular-weight determination by means of an ultracentrifuge gave the formula Au55[P(C6H5)3]Cl6 A model was proposed from Mössbauer spectra by Schmid et al. with cubic close-packing of the 55 gold atoms in a cubeoctahedron as shown in Fig 1. The cluster is almost completely isolated from the surroundings by the twelve triphenylphosphane groups situated in each corner, and the chlorine atoms on the centre of the 3x3 square surfaces. This gives four groups of gold atoms, depending on the different types of surrounding.

Dynamic observations of vesiculation reveal the role of silicate crystals in bubble nucleation and growth in andesitic magmas

Lithos ◽  
2018 ◽  
Vol 296-299 ◽  
pp. 532-546 ◽  
Author(s):  
P. Pleše ◽  
M.D. Higgins ◽  
L. Mancini ◽  
G. Lanzafame ◽  
F. Brun ◽  
...  
Keyword(s):  
Nucleation And Growth ◽  
Bubble Nucleation

Formulation of a Mathematical Process Model for the Foaming of a Mesophase Carbon Precursor

1992 ◽  
Vol 270 ◽  
Author(s):  
S. S. Sandhu ◽  
J. W. Hager
Keyword(s):  
Process Model ◽  
Analytical Description ◽  
Nucleation And Growth ◽  
Bubble Surface ◽  
Bubble Nucleation ◽  
Mesophase Pitch ◽  
Experimental Production ◽  
Mathematical Equations ◽  
Experimental Effort ◽  
Mathematical Process

ABSTRACTMathematical equations have been formulated to guide an experimental effort to produce an open-celled mesophase pitch foam. The formulation provides an analytical description of homogeneous bubble nucleation and growth, diffusion of the blowing gas through the liquid to the bubble surface, and the average material thickness between bubbles. Implications of the formulation for the experimental production of mesophase pitch foam are discussed.

scholarly journals Plasmonic Bubble Nucleation and Growth in Water: Effect of Dissolved Air

2019 ◽  
Vol 123 (38) ◽  
pp. 23586-23593 ◽  
Author(s):  
Xiaolai Li ◽  
Yuliang Wang ◽  
Mikhail E. Zaytsev ◽  
Guillaume Lajoinie ◽  
Hai Le The ◽  
...  
Keyword(s):  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Water Effect ◽  
Dissolved Air

scholarly journals Formation Procedure of Reaction Phases in Al Hot Dipping Process of Steel

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 820 ◽  
Author(s):  
Dongik Shin ◽  
Jeong-Yong Lee ◽  
Hoejun Heo ◽  
Chung-Yun Kang
Keyword(s):  
Phase Diagram ◽  
Steel Surface ◽  
Flow Direction ◽  
Nucleation And Growth ◽  
Boron Steel ◽  
Mechanism Of Reaction ◽  
Dipping Process ◽  
Fe4al13 Phase ◽  
Nucleation And Growth Mechanism ◽  
Dipping Time

This study investigated the nucleation and growth mechanism of reaction layers and phases of hot-dipped boron steel in pure Al at 690 °C for 0–120 s. In the case of a dipping time of 30 s, reaction nuclei of width 10–15 μm and height 10 μm were formed on the steel surface in the flow direction of the liquid Al. This reaction layer was formed as a mixture of θ (Fe4Al13) phase of several nm to 2 μm, θ and η (Fe2Al5) of several nm, a columnar η region, and a β (FeAl) region of 500 nm thickness at the steel interface. At the grain boundaries of ferrite, in contact with the η phase, κ (Fe3AlC) was formed. Using the calculated Fe-Al phase diagram, it was determined that when Fe was dissolved in liquid Al from the steel above 2.5 at% (0.6 wt%), the θ phase was formed. Although most of the θ phases continuously grew toward the liquid phase, the θ phase in contact with the steel was transformed into the η phase with minimal differences in composition due to the inter-diffusion of Al and Fe. It was therefore concluded that the η phase formed at the interface became a growth nucleus and grew in a columnar form toward the steel.

Impact of the Expansion Ratio on the Unsteady Aerodynamics and Performance of a HP Axial Turbine

2016 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
A. Spinelli ◽  
A. Mora
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Flow Direction ◽  
Axial Flow ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
And Performance

In the frame of the European research project RECORD, the flow field within a HP axial-flow turbine model was investigated experimentally for several operating conditions. A number of studies on stator-rotor interaction in HP turbines for subsonic as well as transonic/supersonic conditions were proposed in the last decades, but none of them compared different conditions for the same geometry. In this paper, the transonic condition is investigated and compared to three subsonic ones, in the frame of an entirely new experimental campaign. The research was performed at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy), where a cold-flow, closed-loop test rig is available for detailed studies on turbines and compressors. The boundary conditions resulted in keeping constant both the turbine inlet temperature and the stage outlet absolute flow direction; so far, while the expansion ratio was varied, the rotational speed was also modified accordingly. The analysis was performed by means of a conventional five hole probe in the stator – rotor axial gap and by a fast response aerodynamic probe downstream of the rotor. The local time-averaged and phase-resolved flow field was then derived and used to analyze the stage aerodynamics and performance. Results show that the stage expansion ratio has a dramatic impact on both the rotor aerodynamics and stage performance. In particular, Mach number effects are recognized in the stator cascade that passes from transonic to low subsonic conditions. On the rotor cascade the reduction of expansion ratio reduces significantly the Mach and Reynolds numbers and increases the incidence angle as well; the rotor loss mechanics as well as the vane-rotor interaction are greatly amplified. Correspondingly a significant variation of stage overall efficiency is recorded.

Analysis of Foaming Properties of Asphalt Binder Through a Laser Based Non-Contact Method

2017 ◽  
Author(s):  
Biswajit Kumar Bairgi ◽  
Rafiqul Tarefder
Keyword(s):  
Volume Expansion ◽  
Asphalt Binder ◽  
The United States ◽  
Warm Mix Asphalt ◽  
Expansion Ratio ◽  
Parameter Analysis ◽  
Foaming Properties ◽  
Contact Method ◽  
Contributing Factors ◽  
Foamed Asphalt

Water injected foamed asphalt application in warm mix asphalt (WMA) accounts for more than 90% of all WMA technologies in past several years in the United States (US). Among different asphalt foaming variables: foaming temperatures, foaming water content (FWC), and air pressure are the major controlling factors of foamed asphalt binder characteristics. Foaming induced binder volume expansion and durability of the expanded volume are two contributing factors of foamed asphalt binder properties and foamed mixtures workability. This study evaluates the effect of FWC on foamed asphalt binder properties through a non-contact method. A laser distance meter has been utilized to record the foaming induced binder volume expansion and subsequent foamed bubbles collapse rate. Recently developed four foaming parameters such as expansion ratio (ER), half-life (HL), foaming index (FI), and stability of semis-table foamed binder bubbles (k-values) have been evaluated to characterize foamed asphalt binder. It is seen that addition of higher FWC results in a higher expansion and durability of overall foamed bubbles. Foaming parameter analysis also shows that semi-stable foamed bubbles durability is fairly constant in higher FWCs. Foamed binder rheology is also found to be correlated with FWCs.

Nucleation and Growth of Bubble With the Effects of Solute Gas

Volume 3 ◽  
2004 ◽  
Author(s):  
Shin-Ichi Tsuda ◽  
Shu Takagi ◽  
Yoichiro Matsumoto
Keyword(s):  
Saturation Pressure ◽  
Pressure Change ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Dynamics Simulation ◽  
Pure Liquid ◽  
Dissolved Gas ◽  
High Concentration ◽  
Wrong Prediction ◽  
Solvent Molecules

Bubble nucleation and growth of formed nuclei are investigated by molecular dynamics simulation in Lennard-Jones liquid with gas impurities. For the onset of nucleation from bulk, it has been found that a dissolved gas whose interaction is very weak and whose diameter is larger than that of solvent molecules makes the action to cause composition fluctuation or local phase separation so strong that the nucleation probability predicted from pressure change becomes qualitatively wrong. It has been confirmed that this wrong prediction is generally explained by introducing the superheat ratio nondimensionalized by saturation pressure and spinodal pressure. For the growth stage of formed bubble nuclei, it is observed that the coalescence of nuclei occurs when a weak-interaction gas is dissolved at a high concentration while the competition between neighbor nuclei is dominant in the case of pure liquid.

Steady-State Subcooled Nucleate Boiling on a Downward-Facing Hemispherical Surface

1998 ◽  
Vol 120 (2) ◽  
pp. 365-370 ◽  
Author(s):  
K. H. Haddad ◽  
F. B. Cheung
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Heat Transport ◽  
Bubble Dynamics ◽  
Flow Direction ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Flux

Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low-heat-flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high-heat-flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the increase observed in the critical heat flux in the flow direction along the curved heating surface.

Nanosecond Imaging of Bubble Nucleation on a Microheater

2006 ◽  
Vol 128 (8) ◽  
pp. 734-734 ◽  
Author(s):  
C. Thomas Avedisian ◽  
Richard E. Cavicchi ◽  
Michael J. Tarlov
Keyword(s):  
Thin Film ◽  
Nd:Yag Laser ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Frame Rate ◽  
Vapor Film ◽  
Platinum Surface ◽  
Local Reduction ◽  
Four Corners ◽  
Collapse Phase

These images show bubble nucleation and growth of a thin film heater (a platinum film 15 μm wide, 30 μm long and 0.2 μm thick) that is heated by an 11.8 volt pulse of 0.50 μs duration in subcooled water. Imaging is by illumination from a Nd:Yag laser (hence the green colored photographs) that produces an effective frame rate of 1.3×108 frames/s (the method is described in Avedisian et al. (2006) and Balss et al. (2005)). Time is relative to the first appearance of bubbles. In the early phase, bubbles are visible at the four corners of the platinum surface (58 ns) which grow laterally into a vapor film (142 ns) that covers the surface by 178 ns after which the bubble thickens and grows into the bulk (246 ns and beyond). The collapse phase (e.g., 3.5 μs to 3.8 μs) continues well after the heater pulse is turned off. Vapor completely disappears (3.65 μs) but then bubbles reappear (3.8 μs) well after the power-off phase. Reappearance of bubbles is speculated to be the result of a stagnation-like flow induced by the rapid collapse and inward motion of liquid that jets upward to cause a local reduction of pressure to cavitate a bubble at 3.8 μs. [Avedisian, C.T., Cavicchi, R.E., Tarlov, M.J., Rev. Sci. Instruments, 2006, in press; Balss, K.M., Avedisian, C.T., Cavicchi, R.E., Tarlov, M.J., Langmuir, 21, 10459–10467 (2005)]

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