scholarly journals Accurate determination of bubble size and expansion ratio for polymer foaming with non-isothermal PBB model

2020 ◽  
Author(s):  
Yukai Ge ◽  
Zhiying Fang ◽  
Tao Liu
Keyword(s):  
Bubble Size ◽  
Bubble Growth ◽  
Accurate Determination ◽  
Expansion Ratio ◽  
Term Effect ◽  
Economic Feasibility ◽  
Foaming Agent ◽  
Foaming Process ◽  
Wide Range ◽  
Gas Efficiency

A non-isothermal pressure-balanced bubble-growth (PBB) model has been proposed based on mass, momentum and energy conservation, which additionally considered the decrease in the internal energy of gas due to the work done by gas expansion in bubble. The model could accurately predict the bubble size and expansion ratio for the melt foaming of four polymers for a wide range of cell densities from 1.5×1013 to 1.9×1015 cells/m3. Furthermore, the simulation results indicate that the bubble shell resisted bubble growth and consumed significant energy, preventing the growth of some small nucleations. During the melt foaming process, the energy cost of the linear polymer had a long-term effect, which reduced the bubble size, while that of the long-chain branched polymer had a short-term effect, thereby increasing the expansion ratio. Finally, we defined the gas efficiency of the foaming agent to evaluate the economic feasibility of the foaming agent in a foaming process.

Preparation and Properties of YAG Porous Ceramics via the Casting Method

2018 ◽  
Vol 777 ◽  
pp. 85-89
Author(s):  
Yue Liu ◽  
Yan Yang ◽  
Wang Chen ◽  
Jie Guang Song ◽  
Long He ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Porous Material ◽  
Porous Ceramics ◽  
The Body ◽  
Green Body ◽  
Casting Method ◽  
Foaming Agent ◽  
Blowing Agent ◽  
Foaming Process ◽  
Wide Range

YAG has many excellent features and therefore has a wide range of applications. Preparation and properties of YAG porous ceramics via the casting method is investigated. Through analysis and discussion, the following conclusions can be obtained. With the increase of the content of foaming agent, in the foaming process of the slurry, bubbles generated by the foaming agent and water are gradually increased, the more pores are left in the body after casting, and when the blowing agent is too much, excessive bubbles are generated, which can lead to a very low strength of the green body and can not be formed and operated later. As the ratio of water to material increases, the porosity of the porous material increases. This is because when the blowing agent is constant, the amount of water required for foaming is constant, and the amount of foam generated is also constant. When the content of foaming agent and the ratio of water to material is both 1, the porosity and compressive strength is better.

scholarly journals MR-Based Correction of Brain PET Measurements for Heterogeneous Gray Matter Radioactivity Distribution

1996 ◽  
Vol 16 (4) ◽  
pp. 650-658 ◽  
Author(s):  
Carolyn Cidis Meltzer ◽  
Jon Kar Zubieta ◽  
Jonathan M. Links ◽  
Paul Brakeman ◽  
Martin J. Stumpf ◽  
...  
Keyword(s):  
Gray Matter ◽  
Accurate Determination ◽  
Brain Structures ◽  
Volume Averaging ◽  
Partial Volume Correction ◽  
Sampling Errors ◽  
Partial Volume ◽  
Volume Correction ◽  
Healthy Elderly ◽  
Wide Range

Partial volume and mixed tissue sampling errors can cause significant inaccuracy in quantitative positron emission tomographic (PET) measurements. We previously described a method of correcting PET data for the effects of partial volume averaging on gray matter (GM) quantitation; however, this method may incompletely correct GM structures when local tissue concentrations are highly heterogeneous. We have extended this three-compartment algorithm to include a fourth compartment: a GM volume of interest (VOI) that can be delineated on magnetic resonance (MR) imaging. Computer simulations of PET images created from human MR data demonstrated errors of up to 120% in assigned activity values in small brain structures in uncorrected data. Four-compartment correction achieved full recovery of a wide range of coded activity in GM VOIs such as the amygdala, caudate, and thalamus. Further validation was performed in an agarose brain phantom in actual PET acquisitions. Implementation of this partial volume correction approach in [18F]fluorodeoxyglucose and [11C]-carfentanil PET data acquired in a healthy elderly human subject was also performed. This newly developed MR-based partial volume correction algorithm permits the accurate determination of the true radioactivity concentration in specific structures that can be defined by MR by accounting for the influence of heterogeneity of GM radioactivity.

Lid-Driven Square Cavity Flow: A Benchmark Solution with an 8192x8192 Grid

2021 ◽  
Author(s):  
Carlos Marchi ◽  
Cosmo D. Santiago ◽  
Carlos Alberto Rezende de Carvalho Junior
Keyword(s):  
Reynolds Number ◽  
Stokes Equations ◽  
Accurate Determination ◽  
Stable Solution ◽  
Reynolds Numbers ◽  
Accurate Solution ◽  
Discretization Error ◽  
Square Cavity ◽  
Solution Vector ◽  
Wide Range

Abstract The incompressible steady-state fluid flow inside a lid-driven square cavity was simulated using the mass conservation and Navier-Stokes equations. This system of equations is solved for Reynolds numbers of up to 10,000 to the accuracy of the computational machine round-off error. The computational model used was the second-order accurate finite volume method. A stable solution is obtained using the iterative multigrid methodology with 8192 × 8192 volumes, while degree-10 interpolation and Richardson extrapolation were used to reduce the discretization error. The solution vector comprised five entries of velocities, pressure, and location. For comparison purposes, 65 different variables of interest were chosen, such as velocity profile, its extremum values and location, extremum values and location of the stream function. The discretization error for each variable of interest was estimated using two types of estimators and their apparent order of accuracy. The variations of the 11 selected variables are shown across 38 Reynolds number values between 0.0001 and 10,000. In this study, we provide a more accurate determination of the Reynolds number value at which the upper secondary vortex appears. The results of this study were compared with those of several other studies in the literature. The current solution methodology was observed to produce the most accurate solution till date for a wide range of Reynolds numbers.

USE OF THE MICROWAVE ENERGY FOR ALUMINUM WASTE FOAMING

2019 ◽  
Vol 25 (4) ◽  
pp. 43-49
Author(s):  
LUCIAN PAUNESCU ◽  
MARIUS FLORIN DRAGOESCU ◽  
SORIN MIRCEA AXINTE ◽  
ANA CASANDRA SEBE
Keyword(s):  
Thermal Conductivity ◽  
Compressive Strength ◽  
Porous Structure ◽  
Powder Mixture ◽  
Aluminum Foam ◽  
Fine Powder ◽  
Microwave Energy ◽  
Raw Material ◽  
Foaming Agent ◽  
Foaming Process

The paper presents an aluminum foam experimental technique using the microwave energy. The raw material was recycling aluminum waste processed by ecological melting and gas atomizing to obtain the fine powder required in the foaming process. The powder mixture was completed with dolomite as a foaming agent. The products had a fine and homogeneous porous structure (pore size between 0.4-0.9 mm). The density (1.17-1.19 g/cm3), the compressive strength (6.83-7.01 MPa) and the thermal conductivity (5.71-5.84 W/m·K) had values almost similar to the foams made by conventional methods.

FOAMING AND MOISTURE CROSSLINKING OF VINYL TRIETHOXY SILANE GRAFTED ETHYLENE–PROPYLENE–DIENE TERPOLYMER

2022 ◽  
Author(s):  
Zhengwei Lin ◽  
Qinghong Zhang ◽  
Gongliang Wang ◽  
Jie Mao ◽  
Martin Hoch ◽  
...  
Keyword(s):  
High Efficiency ◽  
Low Cost ◽  
Side Reaction ◽  
High Energy ◽  
Expansion Ratio ◽  
Ethylene Propylene ◽  
Foaming Process ◽  
The Matrix ◽  
High Energy Absorption ◽  
Ethylene Propylene Diene Terpolymer

ABSTRACT Moisture crosslinking of polyolefins has attracted increasing attention because of its high efficiency, low cost, and easy processing. However, the crucial shortcoming of moisture crosslinking is that the side reaction of peroxide scorch (precrosslinking) simultaneously occurs in silane grafting. It has been recognized that making peroxide precrosslinking useful is an effective way to broaden the application of moisture crosslinking. A novel foaming process combined with moisture crosslinking is proposed. The matrix of ethylene–propylene–diene terpolymer grafted with silane vinyl triethoxysilane (EPDM-g-VTES) was prepared by melt grafting, with dicumyl peroxide as initiator. Foaming was then carried out with azodicarbonamide (AC) as the blowing agent by making use of precrosslinking. Subsequently, the EPDM-g-VTES foams were immersed in a water bath to achieve moisture crosslinking with dibutyl tin dilaurate as the catalyst. The results showed that VTES was grafted onto EPDM and the EPDM-g-VTES foams were successfully crosslinked by moisture. The EPDM-g-VTES compounds with AC obtained great cells by compression molding with the help of precrosslinking. The mechanical property of the EPDM-g-VTES foam was improved by moisture crosslinking. The moisture-cured foam with 4 wt% AC had an expansion ratio of about three times, which could bear large deformation and showed a high energy-absorption effect.

Bubble dynamics and oxygen transfer in a hypolimnetic aerator

1998 ◽  
Vol 37 (2) ◽  
pp. 293-300 ◽  
Author(s):  
Vickie L. Burris ◽  
John C. Little
Keyword(s):  
Gas Phase ◽  
Bubble Size ◽  
Oxygen Transfer ◽  
Bubble Dynamics ◽  
Water Flow Rate ◽  
Flow Rates ◽  
Wide Range ◽  
The City ◽  
Close Fit ◽  
Water Supply Reservoirs

A hypolimnetic aerator operating in one of the City of Norfolk's water supply reservoirs was tested. Dissolved oxygen (DO) profiles, water flow rate, and gas-phase holdup were measured over a wide range of applied air flow rates. A model that was developed to predict oxygen transfer in a Speece Cone was modified to conform to the conditions of the hypolimnetic aerator. By varying a single parameter (the initial bubble size) the model was found to provide a close fit to the experimental DO profiles as well as the observed gas-phase holdup. The model was used to show that a doubling in oxygen transfer may be achieved if initial bubble size is reduced from 5 mm to 2.5 mm. Knowing the initial bubble size, it should be possible to predict water velocity by incorporating the effect of momentum. Further work is now underway to test this approach and to examine the possibility of extending this generalized model to cover the range of hypolimnetic aeration and oxygenation devices.

scholarly journals Bitumen Foaming Optimisation Process on the Basis of Rheological Properties

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1854 ◽  
Author(s):  
Marek Iwański ◽  
Grzegorz Mazurek ◽  
Przemysław Buczyński
Keyword(s):  
Half Life ◽  
Expansion Ratio ◽  
Fractional Factorial ◽  
Effective Control ◽  
Maximum Expansion ◽  
Foaming Process ◽  
Original Apparatus ◽  
Foam Properties ◽  
Foamed Bitumen ◽  
Intended Use

This article discusses the results of bitumen foam properties optimisation with respect to three factors: air pressure, bitumen temperature and amount of water. The test materials were unmodified bitumen 50/70 and bitumen 50/70 modified with 2.5% synthetic wax. The experiment was designed according to the 3(3−1) fractional factorial design. The distribution of parameters of bitumen foam were measured with the authors’ original apparatus using a laser beam. This measurement method increased the accuracy of maximum expansion ratio (ER) and half-life (HL) estimation. Based on HL and ER results, it was found that the foaming process increased bitumen stiffness due to the dynamic ageing of the bitumen. The experimental design allows more effective control over the properties of foamed bitumen with respect to its intended use. The presence of synthetic wax extended the half-life of the bitumen foam.

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

2021 ◽  
pp. 026248932110536
Author(s):  
Yun Zhang ◽  
Yadong He ◽  
Chunling Xin ◽  
Yanbin Su
Keyword(s):  
Rare Earth ◽  
Saturation Temperature ◽  
Nucleating Agent ◽  
Expansion Ratio ◽  
Good Effect ◽  
Cell Diameter ◽  
Average Cell ◽  
Foaming Process ◽  
Foaming Temperature ◽  
Crystal Content

The rare earth nucleating agent was used to modify block copolymerized polypropylene (PPB) in foaming process. The results show that the crystallization of PPB and the melting temperature of β-crystal increased gradually with increased β-crystal nucleating agent content. The total crystallinity decreased with amount of addition increasing, and the relative content of β-crystal increased first and then decreased. When β-crystal nucleating agent content was 0.4 wt%, the relative β-crystal content reached the maximum value of 95.27%, and the final crystal grain refinement significantly. The addition of rare earth β-crystal nucleating agent has a good effect on improving the uniformity of foam cells. Under the same content of β-crystal nucleating agent and pressure, the average cell diameter and expansion ratio increased with the saturation temperature increasing. After the foaming temperature reaches 155°C, the expansion ratio began to decrease, which was also consistent with the changed trend of relative β-crystal content. At the same content of temperature and relative β-crystal, as the foaming pressure increased, the cell diameter decreased gradually, and the expansion ratio increased first, and then decreased.

scholarly journals Determining Girard Form Class in Central Hardwoods

1997 ◽  
Vol 14 (4) ◽  
pp. 202-206 ◽  
Author(s):  
John C. Rennie ◽  
Jack D. Leake
Keyword(s):  
Direct Measurement ◽  
Accurate Determination ◽  
Tree Form ◽  
Form Class ◽  
Wide Range ◽  
Close Proximity ◽  
Wedge Prism ◽  
The Cost ◽  
Volume Estimates

Abstract Girard form class is widely used to describe tree form. Tree volume estimates change about 3% per unit change of Girard form class (Mesavage and Girard 1946). Hardwoods growing in close proximity have been observed to have a wide range in Girard form class. Accurate determination of Girard form class can therefore be important in getting accurate estimates of hardwood timber volume. However, the cost of estimating Girard form class for every tree being measured in the stand would be prohibitively expensive. Thus, estimation of average Girard form class for a stand is considered here. Three instruments used to estimate Girard form class—a Wheeler pentaprism optical caliper, a wedge prism, and a Spiegel relaskop—were compared to direct measurement. Number of sample trees to achieve desired half-widths of the confidence interval of ±1 and ±1 1/2 units of Girard form class was calculated for each method. Direct measurement requires the fewest trees to achieve the desired results. However, it requires considerably more time per tree than any of the instruments tested. The Wheeler pentaprism requires only a few more trees than direct measurement, and considerably fewer trees than either the wedge prism or the Spiegel relaskop. Use of all three instruments is hindered when understory vegetation obscures the top of the first log. North. J. Appl. For. 14(4):202-206.

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