Optimal Packing Density Research Articles

Design and optimization of gradient fibrous media using the method of moments

The goal of this work is to optimize the deposition mass distribution of polydisperse particles inside the fibrous media by modifying the distribution of the fiber packing density across filter depth. Two types of gradient fibrous media with linear and exponential fiber packing density distribution along the flow direction were derived. The method of moments was employed to study the transport and deposition characteristics of polydisperse aerosol particles inside the fibrous media. The reliability of the calculated results by the method of moments was confirmed by the numerical simulations based on the discrete phase model (DPM). Results indicate that the gradient fibrous media allows more particles to transport and deposit into the interior of the fibrous media, which improves the uniformity of particle deposition distribution across filter depth. There exists an optimal fiber packing density distribution ratio for the gradient fibrous media where the non-uniformity of deposition mass distribution of polydisperse particles across filter depth is minimized. In this way, uniform deposition distribution along the flow direction can be generally achieved by optimizing the fiber packing density distribution, which will contribute to the optimal design of microstructures for the fibrous filter.

Influence of framing coil orientation and its shape on the hemodynamics of a basilar aneurysm model.

Aneurysms are bulges of an artery, which require clinical management solutions. Due to the inherent advantages, endovascular coil filling is emerging as the treatment of choice for intracranial aneurysms (IAs). However, after successful treatment of coil embolization, there is a serious risk of recurrence. It is well known that optimal packing density will enhance treatment outcomes. The main objective of endovascular coil embolization is to achieve flow stasis by enabling significant reduction in intra-aneurysmal flow and facilitate thrombus formation. The present study numerically investigates the effect of framing coil orientation on intra-aneurysmal hemodynamics. For the purpose of analysis, actual shape of the embolic coil is used, instead of simplified ideal coil shape. Typically used details of the framing coil are resolved for the analysis. However, region above the framing coil is assumed to be filled with a porous medium. Present simulations have shown that orientation of the framing coil loop (FCL) greatly influences the intra-aneurysmal hemodynamics. The FCLs which were placed parallel to the outlets of basilar tip aneurysm (Coil A) were found to reduce intra-aneurysmal flow velocity that facilitates thrombus formation. Involving the coil for the region is modeled using a porous medium model with a packing density of 20 . The simulations indicate that the framing coil loop (FCL) has a significant influence on the overall outcome.

Additively manufactured structures with powder inclusions for controllable dissipation: The critical influence of packing density

Particle dampers represent a simple yet effective means to reduce unwanted oscillations when attached to structural components. Powder bed fusion additive manufacturing of metals allows to integrate particle inclusions of arbitrary shape, size, and spatial distribution directly into bulk material, giving rise to novel metamaterials with controllable dissipation without the need for additional external damping devices. At present, however, it is not well understood how the degree of dissipation is influenced by the properties of the enclosed powder packing. In the present work, a two-way coupled discrete element - finite element model is proposed allowing for the first time to consistently describe the interaction between oscillating deformable structures and enclosed powder packings, while existing works have only considered rigid enclosures so far. As fundamental test case, the free oscillations of a hollow cantilever beam filled with various powder packings differing in packing density, particle size, and surface properties are considered to systematically study these factors of influence. Critically, it is found that the damping characteristics strongly depend on the packing density of the enclosed powder and that an optimal packing density exists at which the dissipation is maximized. Moreover, it is found that the influence of (absolute) particle size on dissipation is rather small. First-order analytical models for different deformation modes of such powder cavities are derived to shed light on this observation.

Hemodynamic analysis of coil filled patient-specific middle cerebral artery aneurysm using porous medium approach

Cerebral aneurysms are bulges of an artery, which could be life-threatening when ruptured. Depending on their size, shape, and location, they need to be managed either through clipping or an endovascular coiling intervention. When coiled, reduced hemodynamic activity enables the coil to get thrombosed and achieve flow stasis. However, some coils delivered into the aneurysm tend to prolapse into the parent vessel and cause stroke due to obstruction and embolization. The recurrence of an aneurysm after endovascular coiling is of concern in the treatment of wide necked aneurysms. The initial packing density or improper coiling of the aneurysm and its relation to recurrence remains uncertain. This study investigates the influence of reduction in coil fill volume and packing density on the aneurysm recurrence using hemodynamic parameters by analyzing its flow features. Finite element method based commercial computational fluid dynamics solver is employed for performing patient-specific simulations for the coil filled aneurysm. The present approach uses porous medium based formulation. The numerical simulations show that any reduction below the optimal coil fill volume and packing density inside the aneurysm increases the velocity magnitude, wall shear stress, time-averaged wall shear stress, and spatial gradient of wall shear stress and reduces the relative residence time. The hemodynamic parameters and flow features suggest that a reduction in the coil packing density inside the aneurysm increases the chances of aneurysm recurrence. Hence, an assessment on how to achieve optimal coil fill volume and packing density is critical in reducing the risk of aneurysm recurrence.

Influence of Packing Density on Electrochemical Performance of Lignin

Abstract Bio-based carbonaceous materials such as lignin are taking up increasingly important roles in energy storage. However, the wide spectrum of molecular identity and structure of lignin lead to inconsistent structure, properties, and performance because of its source, extraction, and pretreatment processes. In this research, we investigate the effects of packing density on the electrochemical performance for lignin. Samples were synthesized using lignin as the electroactive material. Four distinct types of lignin, i.e., alkali lignin microparticles (MP), alkali lignin nanoparticles (NP), dealkaline lignin MP, and dealkaline lignin NP, were used in this study. They were studied through varying the packing density and its subsequent effects on the electrochemical performance. The scanning electron microscopy and Fourier-transform infrared spectrometry analysis were conducted to obtain morphology and chemical compositions. Cyclic voltammetry and cyclic charge discharge tests were conducted to evaluate the polarization resistance. The optimal packing density was found to be in the range of 0.35–0.50 g cm−3 for all samples. In the optimal packing density range, dealkaline lignin NP displayed the highest electrochemical performance with a maximum specific capacitance of 1,159 mF g−1, an energy density of 19.097 Wh kg−1, and a power density of 11.05 kW kg−1. The optimization of packing density would enable further development of lignin-containing energy storage devices such as supercapacitors.

Strategies to overcome the limitations of cross-linked hydrophilic PVA membranes; carboxy methyl cellulose blending for epichlorohydrin-isopropanol-water pervaporation dehydration

Sodium carboxyl methyl cellulous (NaCMC)/Polyvinyl alcohol (PVA) coated Alumina hollow fiber (AHF) membrane was developed and applied to dehydration of ECH-IPA-water ternary feed mixture. CMC40 membrane, including 40 wt% of NaCMC showed the highest flux of 0.416 kg/m2h and a separation factor of 898 due to optimized packing density between PVA and the NaCMC polymer chain and relatively higher hydrophilic nature for PV separation to ECH-IPA-water ternary feed. After that, CMC40-coated AHF membrane was prepared according to the number of CMC40 coating and baking temperature. With an increase in baking temperature to 170 °C, the separation factor was significantly improved, while the flux decreased slightly. Moreover, NaCMC40-AHF showed robust properties with stable performance in the 50-h long-term PV test.

Fabrication of highly permeable PDMS@ZIF‐8/PVDF hollow fiber composite membrane in module for ethanol‐water separation

AbstractThe construction of high‐performance MOF‐based hollow fiber composite membrane (HFCM) modules is a significant, yet challenging task for the biofuel production industry. In this study, a novel approach was taken to fabricate PDMS@ZIF‐8/PVDF HFCMs in modules through a facile ZIF‐8 self‐crystallization synthesis followed by pressure‐assisted PDMS infusion for pervaporation ethanol‐water separation. The as‐prepared HFCMs exhibited an ultrathin separation layer (thickness, 370 ± 35 nm), which was achieved through precise regulation of the ZIF‐8 membrane and defect repair by PDMS infusion. Moreover, the strategy utilized in this study resolved the defect issues arising from MOF agglomeration in conventional composite membranes. Impressively, at the optimal packing density, the prepared membrane demonstrated a remarkable ethanol flux (1.11 kg m−2 h−1) with an PSI value (26.59 kg m−2 h−1) and showed promising long‐term stability for the pervaporation of 5 wt% ethanol aqueous solution at 40°C.

New lower bounds for optimal horoball packing density in hyperbolic n-space for 6 le n le 9

Koszul type Coxeter simplex tilings exist in hyperbolic n-space mathbb {H}^n up to n = 9, and their horoball packings achieve the highest known regular ball packing densities for n = 3, 4, 5. In this paper we determine the optimal horoball packing densities of Koszul simplex tilings in dimensions 6 le n le 9, which give new lower bounds for optimal packing density in each dimension. The symmetries of the packings are given by Coxeter simplex groups, and a parameter related to the Busemann function gives an isometry invariant description of different optimal horoball packing configurations.

Evaluation of three non-linear packing density models on micropowder mixtures

The formulation of powders often requires an optimized packing density of the granular skeleton which takes into account the desired properties. More accurate than the conventional linear models, three non-linear packing density models are evaluated from published data on binary or ternary mixtures of alumina powders, glass microbeads, siliceous microaggregates: the Compressible Packing Model (CPM), the 3-parameter Particle Packing Model (3PPM), the Theoretical Packing Density Model (TPDM). Depending on the models, they involve a compaction index K and certain particle interactions: the loosening effect a and possibly the critical cavity size ratio x0 from which it appears, the wall effect b and the wedging effect c. The CPM (with a, b, K), by incorporating only 2 interaction functions for a and b, reduces its versatility but is efficient for siliceous. The 3PPM (with a, b, c), by incorporating 9 interaction functions, adapts well to the various micropowders with however a lower performance for the siliceous for which the packing densities predicted in “compacted” conditions are lower than in “uncompacted” conditions. The TPDM (with a, b, K, x0) is effective for all types of micropowders and generates the best statistical indicators.

Flow and transport in a pleated filter

A pleated membrane filter consists of a porous membrane layer, which is surrounded by two supporting layers, and the whole structure is pleated and placed into a cylindrical cartridge. Pleated membrane filters are used in a variety of industrial applications, since they offer more surface area to volume ratio that is not found in equivalent flat filters. In this work, we introduce a novel three-dimensional model of a pleated membrane filter that consists of an empty region, a pleated region, and a hollow region. The advection diffusion equation is used to model contaminant concentration in the membrane pores along with Darcy's law to model the flow within the membrane and support layers, while the Stokes equation is used for the flow in the empty region and the hollow region. We further use the key assumptions of our model based on small aspect ratios of the filter cartridge and the pleated membrane to simplify the governing equations, which can be easily solved by numerical methods. By performing these steps, we seek to discover an optimal pleat packing density to find the optimum filter performance, while not exceeding a threshold for the particle concentration at the filter outlet.

"Porous and Yet Dense" Electrodes for High-Volumetric-Performance Electrochemical Capacitors: Principles, Advances, and Challenges.

With the ever‐rapid miniaturization of portable, wearable electronics and Internet of Things, the volumetric performance is becoming a much more pertinent figure‐of‐merit than the conventionally used gravimetric parameters to evaluate the charge‐storage capacity of electrochemical capacitors (ECs). Thus, it is essential to design the ECs that can store as much energy as possible within a limited space. As the most critical component in ECs, “porous and yet dense” electrodes with large ion‐accessible surface area and optimal packing density are crucial to realize desired high volumetric performance, which have demonstrated to be rather challenging. In this review, the principles and fundamentals of ECs are first observed, focusing on the key understandings of the different charge storage mechanisms in porous electrodes. The recent and latest advances in high‐volumetric‐performance ECs, developed by the rational design and fabrication of “porous and yet dense” electrodes are then examined. Particular emphasis of discussions then concentrates on the key factors impacting the volumetric performance of porous carbon‐based electrodes. Finally, the currently faced challenges, further perspectives and opportunities on those purposely engineered porous electrodes for high‐volumetric‐performance EC are presented, aiming at providing a set of guidelines for further design of the next‐generation energy storage devices.

Modeling and improvement of a packed bed latent heat storage filled with non-spherical encapsulated PCM-Elements

A thermal energy storage filled with a packed bed of macro-encapsulated latent heat storage elements is studied. Such a storage can be used in combination with, for example, a solar thermal heating system. Conventional capsule designs based on spherical shape do not allow for optimal packing density and heat transfer within the capsule. Therefore, capsule designs were introduced, which deviate from this basic geometry. These designs are built upon a super-ellipsoidal shape with multiple surface extensions, e.g. holes and grooves, in order to enhance heat transfer.To further optimize the thermal performance of the storage system, a model describing the charging and discharging processes of the heat storage was developed based on a new approach for the treatment of non-spherical capsules. The model was validated against experimental temperature data obtained from charging and discharging measurements with flow rates ranging from 216 to 1000 kg/h. The maximal observed deviation between simulation and experiment was ±0.82 K.Furthermore, new capsule geometries based on super-ellipsoids were evaluated with respect to their storage capacity and thermal power output. A promising capsule design was identified which has a more than 20% higher storage capacity than the other shapes and provides a reasonable thermal power output of approximately 4 kW during the phase change of the storage material. The energy density was increased from 51.5 kWh/m³ to 64.1 kWh/m³.

Binder Jetting Additive Manufacturing: Effect of Particle Size Distribution on Density

Abstract This paper reports a study on the effects of particle size distribution (tuned by mixing different-sized powders) on density of a densely packed powder, powder bed density, and sintered density in binder jetting additive manufacturing. An analytical model was used first to study the mixture packing density. Analytical results showed that multimodal (bimodal or trimodal) mixtures could achieve a higher packing density than their component powders and there existed an optimal mixing fraction to achieve the maximum mixture packing density. Both a lower component particle size ratio (fine to coarse) and a larger component packing density ratio (fine to coarse) led to a larger maximum mixture packing density. A threshold existed for the component packing density ratio, below which the mixing method was not effective for density improvement. Its relationship to the component particle size ratio was calculated and plotted. In addition, the dependence of the optimal mixing fraction and maximum mixture packing density on the component particle size ratio and component packing density ratio was calculated and plotted. These plots can be used as theoretical tools to select parameters for the mixing method. Experimental results of tap density were consistent with the above-mentioned analytical predictions. Also, experimental measurements showed that powders with multimodal particle size distributions achieved a higher tap density, powder bed density, and sintered density in most cases.

Additive Lithography-Organic Monolayer Patterning Coupled with an Area-Selective Deposition.

The combination of area-selective deposition (ASD) with a patternable organic monolayer provides a versatile additive lithography platform, enabling the generation of a variety of nanoscale feature geometries. Stearate hydroxamic acid self-assembled monolayers (SAMs) were patterned with extreme ultraviolet (λ = 13.5 nm) or electron beam irradiation and developed with ASD to achieve line space patterns as small as 50 nm. Density functional theory was employed to aid in the synthesis of hydroxamic acid derivatives with optimized packing density to enhance the imaging contrast and improve dose sensitivity. Near-edge X-ray absorption fine structure spectroscopy and infrared spectroscopy reveal that the imaging mechanism is based on improved deposition inhibition provided by the cross-linking of the SAM to produce a more effective barrier during a subsequent deposition step. With patterned substrates composed of coplanar copper lines and silicon spacers, hydroxamic acids selectively formed monolayers on the metal portions and could undergo a pattern-wise exposure followed by ASD in the first combination of a patternable monolayer with ASD. This material system presents an additional capability compared to traditional ASD approaches that generally reflect a starting patterned surface. Furthermore, this bottoms-up additive approach to lithography may be a viable alternative to subtractive nanoscale feature generation.

Functional Molecular Interfaces for Impedance-Based Diagnostics.

In seeking to develop and optimize reagentless electroanalytical assays, a consideration of the transducing interface features lies key to any subsequent sensitivity and selectivity. This review briefly summarizes some of the most commonly used receptive interfaces that have been employed within the development of impedimetric molecular sensors. We discuss the use of high surface area carbon, nanoparticles, and a range of bioreceptors that can subsequently be integrated. The review spans the most commonly utilized biorecognition elements, such as antibodies, antibody fragments, aptamers, and nucleic acids, and touches on some novel emerging alternatives such as nanofragments, molecularly imprinted polymers, and bacteriophages. Reference is made to the immobilization chemistries available along with a consideration of both optimal packing density and recognition probe orientation. We also discuss assay-relevant mechanistic details and applications in real sample analysis.

Development of gravitational search algorithm model for predicting packing density of cementitious pastes

Wet packing approach is recently used to design different kinds of concrete. To achieve an optimal particle packing density, the particles should be chosen in a way to fill the voids between larger particles with smaller ones for obtaining a dense and stiff particle structure. The majority of past research on packing density has focused on the evaluation of the particle size distribution of granular matrix to gain improvements in the packing density of cementitious materials, while limited attention has been paid to the construction of a model to estimate the packing density value. To serve that purpose, in this study, a series of 216 collected samples were used for proposing a model. The dataset was divided into two main sets for construction and verification of the model. As the basis for the packing density modeling, use of the gravitational search algorithm (GSA) was proposed. Design of experiment (DOE) software was used to evaluate the contribution of each variable on the proposed model. The outcomes indicate that among different parameters, water amount has the largest effect on the packing density value of cementitious pastes. Moreover, increases in the amounts of supplementary cementitious materials up to certain levels increase the packing density. The coefficient of variation (CoV) of the proposed model is 6.3% which reflects the accuracy and consistency of the model.

New horoball packing density lower bound in hyperbolic 5-space

We describe the optimal horoball packings of asymptotic Koszul type Coxeter simplex tilings of $5$-dimensional hyperbolic space where the symmetries of the packings are generated by Coxeter groups. We find that the optimal horoball packing density of $\delta_{opt}=0.59421\dots$ is realized in an entire commensurability class of arithmetic Coxeter tilings. Eleven optimal arrangements are achieved by placing horoballs at the asymptotic vertices of the corresponding Coxeter simplices that give the fundamental domains. When multiple horoball types are allowed, in the case of the arithmetic Coxeter groups, the relative packing densities of the optimal horoball types are rational submultiples of $\delta_{opt}$, corresponding to the Dirichlet-Voronoi cell densities of the packing. The packings given in this paper are so far the densest known in hyperbolic $5$-space.

Sustainable design and ecological evaluation of low binder self-compacting concrete

Self-compacting concrete (SCC) is a kind of high-performance concrete that is able to consolidate under its own weight without vibration. Due to its high binder content, the production of SCC normally needs a larger number of cement, the production of cement are associated with high energy consumption and CO2 emissions, which result in serious environmental pollution. To maintain the ecological sustainability of SCC, this research recommends a sustainable mix design method for SCC with a low binder content based on particle packing theory. The packing density of the concrete mixture is optimized by selecting an appropriate powder composition and particle gradation of the aggregate. Using the SCC mix design with the optimal packing density, a sustainable SCC can be achieved with the lowest possible of binder content while maintaining the desired level of workability and mechanical performance. The proposed design reduces the required binder content in the SCC mixture by 16%, the energy consumption during production of concrete by 30.57%, the CO2 emissions by 33.98%, and the material cost by 6.24%, respectively, compared with the typical mix design recommended by the American Concrete Institute (ACI C237) standard for similar 28-day compressive strength. The proposed mix design strikes a good balance between the ecological sustainability and performance based behaviors of SCC.

Optimal packing of material flow on conveyor belts

We are interested in an optimal packing density problem for material flows on conveyor belts in two spatial dimensions. The control problem is concerned with the initial configuration of parts on the belt to ensure a high overall flow rate and to further reduce congestion. An adjoint approach is used to compare the optimization results from the microscopic model based on a system of ordinary differential equations with the corresponding macroscopic model relying on a hyperbolic conservation law. Computational results highlight similarities and differences of both optimization models and emphasize the benefits of the macroscopic approach.

Inorganic scintillation detectors based on Eu-activated phosphors for 192Ir brachytherapy

The availability of real-time treatment verification during high-dose-rate (HDR) brachytherapy is currently limited. Therefore, we studied the luminescence properties of the widely commercially available scintillators using the inorganic materials Eu-activated phosphors Y2O3:Eu, YVO4:Eu, Y2O2S:Eu, and Gd2O2S:Eu to determine whether they could be used to accurately and precisely verify HDR brachytherapy doses in real time. The suitability for HDR brachytherapy of inorganic scintillation detectors (ISDs) based on the 4 Eu-activated phosphors in powder form was determined based on experiments with a 192Ir HDR brachytherapy source. The scintillation intensities of the phosphors were 16–134 times greater than that of the commonly used organic plastic scintillator BCF-12. High signal intensities were achieved with an optimized packing density of the phosphor mixture and with a shortened fiber-optic cable. The influence of contaminating Cerenkov and fluorescence light induced in the fiber-optic cable (stem signal) was adequately suppressed by inserting between the fiber-optic cable and the photodetector a 25 nm band-pass filter centered at the emission peak. The spurious photoluminescence signal induced by the stem signal was suppressed by placing a long-pass filter between the scintillation detector volume and the fiber-optic cable. The time-dependent luminescence properties of the phosphors were quantified by measuring the non-constant scintillation during irradiation and the afterglow after the brachytherapy source had retracted. We demonstrated that a mixture of Y2O3:Eu and YVO4:Eu suppressed the time-dependence of the ISDs and that the time-dependence of Y2O2S:Eu and Gd2O2S:Eu introduced large measurement inaccuracies. We conclude that ISDs based on a mixture of Y2O3:Eu and YVO4:Eu are promising candidates for accurate and precise real-time verification technology for HDR BT that is cost effective and straightforward to manufacture. Widespread dissemination of this technology could lead to an improved understanding of error types and frequencies during BT and to improved patient safety during treatment.