Sensitivity of particle loss to the Kelvin effect in LES of young contrails

Abstract. Different treatments of the Kelvin effect in LES modeling of early contrails are shown to cause variations in the survival rate of ice particles by up to a factor of 4 and in optical depth and mean particle size by up to 50 %. The Kelvin effect which varies exponentially with particle size, can reduce or even suppress the impact of other important ambient parameters, such as ice supersaturation, on particle survival rate. Lowering or neglecting the Kelvin effect is shown to substantially alter the evolution of the ice particle size distribution and delay the onset of particle loss. A strongly Kelvin effect dependent exponential relation between particle survival rate and particle size is shown for high EIsoot (O(1015)).

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A SIMULATION STUDY ON THE EFFECT OF PARTICLE SIZE DISTRIBUTION ON THE PRINTED GEOMETRY IN SELECTIVE LASER MELTING

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4052705 ◽

2021 ◽

pp. 1-14

Author(s):

Vaishak Ramesh Sagar ◽

Samuel Lorin ◽

Johan Göhl ◽

Johannes Quist ◽

Christoffer Cromvik ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Layer Thickness ◽

Selective Laser Melting ◽

Laser Melting ◽

Powder Bed ◽

Mean Particle Size ◽

Final Layer ◽

Effect Of Particle Size

Abstract Selective laser melting (SLM) process is a powder bed fusion additive manufacturing process that finds applications in aerospace and medical industries for its ability to produce complex geometry parts. As the raw material used is in powder form, particle size distribution (PSD) is a significant characteristic that influences the build quality in turn affecting the functionality and aesthetics aspects of the product. This paper investigates the effect of PSD on the printed geometry for 316L stainless steel powder, where three coupled in-house simulation tools based on Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), and Structural Mechanics are employed. DEM is used for simulating the powder bed distribution based on the different powder PSD. The CFD is used as a virtual testbed to determine thermal parameters such as heat capacity and thermal conductivity of the powder bed viewed as a continuum. The values found as a stochastic function of the powder distribution is used to analyse the effect on the melted zone and deformation using Structural Mechanics. Results showed that mean particle size and PSD had a significant effect on the packing density, melt pool layer thickness, and the final layer thickness after deformation. Specifically, a narrow particle size distribution with smaller mean particle size and standard deviation produced solidified final layer thickness closest to nominal layer thickness. The proposed simulation approach and the results will catalyze in development of geometry assurance strategies to minimize the effect of particle size distribution on the geometric quality of the printed part.

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Green Preparation, Spheroidal, and Superior Property of Nano-1,3,5,7-Tetranittro-1,3,5,7-Tetrazocane

Journal of Nanomaterials ◽

10.1155/2018/5839037 ◽

2018 ◽

Vol 2018 ◽

pp. 1-8 ◽

Cited By ~ 5

Author(s):

Xinlei Jia ◽

Jingyu Wang ◽

Conghua Hou ◽

Yingxin Tan

Keyword(s):

Activation Energy ◽

Particle Size ◽

Fractal Dimension ◽

Particle Size Distribution ◽

Size Distribution ◽

Fractal Theory ◽

Crystal Form ◽

Decomposition Temperature ◽

Scanning Calorimetry ◽

The Impact

Herein, a green process for preparing nano-HMX, mechanical demulsification shearing (MDS) technology, was developed. Nano-HMX was successfully fabricated via MDS technology without using any chemical reagents, and the fabrication mechanism was proposed. Based on the “fractal theory,” the optimal shearing time for mechanical emulsification was deduced by calculating the fractal dimension of the particle size distribution. The as-prepared nano-HMX was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). And the impact sensitivities of HMX particles were contrastively investigated. The raw HMX had a lower fractal dimension of 1.9273. The ideal shearing time was 7 h. The resultant nano-HMX possessed a particle size distribution ranging from 203.3 nm to 509.1 nm as compared to raw HMX. Nano-HMX particles were dense spherical, maintaining β-HMX crystal form. In addition, they had much lower impact sensitivity. However, the apparent activation energy as well as thermal decomposition temperature of nano-HMX particles was decreased, attributing to the reduced probability for hotspot generation. Especially when the shearing time was 7 h, the activation energy was markedly decreased.

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Theoretical analysis of particle size re-distribution due to Ostwald ripening in the fuel cell catalyst layer

Open Physics ◽

10.1515/phys-2019-0081 ◽

2019 ◽

Vol 17 (1) ◽

pp. 779-789 ◽

Cited By ~ 2

Author(s):

Ambrož Kregar ◽

Tomaž Katrašnik

Keyword(s):

Particle Size ◽

Fuel Cells ◽

Fuel Cell ◽

Particle Size Distribution ◽

Size Distribution ◽

Electric Potential ◽

Ostwald Ripening ◽

Particle Growth ◽

Mean Particle Size ◽

Fuel Cell Catalyst

Abstract The limited durability of hydrogen fuel cells is one of the main obstacles in their wider adoption as a clean alternative technology for small scale electricity production. The Ostwald ripening of catalyst material is recognized as one of the main unavoidable degradation processes deteriorating the fuel cell performance and shortening its lifetime. The paper systematically studies how the modeling approach towards the electrochemically driven Ostwald ripening in the fuel cell catalyst differs from the classical diffusion driven models and highlights how these differences affect the resulting evolution of particle size distribution. At moderately low electric potential, root-law growth of mean particle size is observed with linear relation between mean particle size and standard deviation of particle size distribution, similar to Lifshitz-Slyozov-Wagner theory, but with broader and less skewed distribution. In case of high electric potential, rapid particle growth regime is observed and qualitatively described by redeposition of platinum from a highly oversaturated solution, revealing the deficiencies of the existing platinum degradation models at describing the Ostwald ripening in the fuel cells at high electric potentials. Several improvements to the established models of platinum degradation in fuel cell catalysts are proposed, aimed at better description of the diffusion processes involved in particle growth due to Ostwald ripening.

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