Effect Of Carbon Particle Size Research Articles

Effect of Carbon Particle Feeding as Radiant Absorbent for Enhanced Heat Transfer

Abstract Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000 °C would increase the surface and would recover the original activity as catalyst. In a windowed solar reactor, carbon particles are directly exposed to the high flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in a solar reactor is the presence and transport of carbon particles. In this paper, a transient one-dimensional model is presented to describe the effect of carbon particle feeding on energy transport and temperature profile of a cavity-type solar receiver. The model was developed by dividing the receiver into several control volumes and formulating energy balance equations for gas phase, particles, and cavity walls within each control volume. Monte Carlo ray tracing method was used to determine the solar heat absorbed by particles and cavity walls, as well as the radiative exchange between particles and cavity walls. Model accuracy was verified by experimental work using a solar receiver where carbon particles were injected uniformly. Comparison of simulation results with the experimentally measured temperatures at three different locations on cavity receiver wall showed an average deviation of 3.81%. The model was then used to study the effect of carbon particle size and feeding rate on the heat transfer, temperature profile, and energy absorption of the solar receiver. Based on the simulation results, it was found that injection of carbon particles with a size bigger than 500 µm has no significant influence on heat transfer of the system. However, by reducing the particle size lower than 500 µm, temperature uniformity and energy absorption can be enhanced.

Adsorption Isotherm of Carbon Microparticles Prepared from Pumpkin (Cucurbita maxima) Seeds for Dye Removal

This study aims to evaluate the adsorption isotherm of carbon microparticles prepared from pumpkin (Cucurbita maxima) seeds for adsorbing curcumin (as a model of dye). The results were derived and compared using the kinetics approach based on several standard adsorption isotherm models, namely the Langmuir, Temkin, Freundlich, and Dubinin-Radushkevich models. The second aim is to evaluate the effects of carbon particle size (from 100 to 1000 mm) on the adsorption characteristics. The experimental results showed that the adsorption on the surface of carbon microparticles occurred in monolayer with a physical phenomenon. This is because the active areas are located only on the outer surface of carbon and no surface structure in the carbon is available. This is confirmed by the fact that the produced carbon has less porosity and the pores themselves are mostly produced from the release of inorganic contents during carbon synthesis, while the amount of inorganic content is very less. The confirmation of the adsorption profile was also achieved by testing various sizes of carbon microparticles. Smaller particles have direct impacts on the improvement of adsorption capacity, which is due to the existence of a larger surface area, a larger number of adsorption sites, and additional cooperative adsorption, i.e. adsorbate-adsorbate interaction. Understanding the adsorption phenomena occurring on carbon particles is useful for further developments and applications, such as those of catalysts and adsorbents, especially concerning the production of carbon materials from organic waste.

Experimental Investigation and Numerical Determination of Custom Gas Diffusion Layers on PEMFC Performance

The objective of this work is to investigate the design of gas diffusion layer (GDL) for fuel cells that possess specific transport properties. Various types of custom GDLs that have a microporous bilayer (MP) were studied. These GDLs have two different MP layers and a carbon substrate. GDLs with different bilayer MPs designs were tested and the fuel cells performance was investigated. The performance of the fuel cell was measured in-situ with different GDLs at several operating conditions. The pore morphology of the GDLs as well as pore size distribution of the GDLs including the MPs was determined. The data on the pore size distribution including the relationship between tortuosity and porosity was used as model parameters. The experimental data and model predictions confirm that introducing the bilayer MPs on the substrate could improve the transport resistant and increase the performance of PEMFC. The effect of carbon particle size and overall diffusivity also modified the value of MacMullin number and overall thickness of GDL causing the differences in performance and local distributions.

Effect of Carbon Particle Size and Content on the Mechanical and Thermal Properties of Recycled SLS Glass Composite

Glass-composite materials were prepared from the soda lime silicate (SLS) waste glass; ball clay and charcoal powder were fired to temperature of 850 °C as an effort for recycling waste glass. Various carbon contents, i.e., 1, 5, 10, 20 and 30 wt.% C were used to evaluate the effect of carbon contents on the hardness and thermal properties of glass composites. In addition, five different particles size (d0.5) of 1, 5, 20, 40 and 75 μm were used to observe the influence of particle size on the physical and mechanical properties of the glass composites. Phase analysis studies revealed the presence of quartz (ICDD: 00001-0649, 2θ = 25.6° and 35.6°), cristobalite (ICDD 00004-0379, 2θ = 22.0° and 38.4°) and wollastonite (ICDD 00002-0689, 2θ = 30.1° and 26.9°). The results showed that the optimised properties is at 1 wt.% of carbon content containing average pore size of 10 μm, with lowest porosity percentage of 1.76 %, highest Vickers microhardness of 4.6 GPa and minimum CTE. The percentage of porosity and hardness value also increased with reduction in carbon particle size.

Enzyme Electrode Platform Using Methyl Viologen Electrochemically Immobilized on Carbon Materials

This paper presents the electrochemical stabilization of methyl viologen cations on a variety of carbon materials using a glassy carbon electrode. Three different types of voltammetry (potential hold, triangular wave, and square wave voltammetry) were used to stabilize the methyl viologen cation. Methyl viologen cation-modified multi-walled carbon nanotubes (MWCNTs) of different diameters and with various functional groups were examined to observe the effects of carbon particle size and surface modification. Various carbon materials containing MWCNTs, acetylene black, Super P, Vulcan XC-72, and Ketjenblack were modified by methyl viologen and then electrochemically characterized. Their electrochemical behaviors are discussed in terms of carbon properties, such as pore structure and electrical conductivity. Carbon with immobilized the methyl viologen cation and glucose oxidase was assessed to confirm its feasibility for enzyme electrode applications.

Analytical Modeling of Effective Diffusivity in Micro-Porous Layers

The membrane electrode assembly (MEA) used in polymer electrolyte fuel cells consists of a membrane, two electrodes (anode and cathode), and two gas diffusion layers (GDLs). The GDL is responsible for providing the pathways for transport of the reactant gases from the flow channels to the catalyst layers. Hence, the mass transport resistance of this layer should be minimized for high performance operation. The GDL is typically a dual-layer carbon-based material composed of a macro-porous substrate, which usually contains carbon fibers, binder, and PTFE, and a thin delicate micro-porous layer (MPL), which is usually made of carbon nano-particles and PTFE. Spherical carbon nano-particles of 20-100 nm in diameter construct the complex structure of MPL. Small pore sizes and highly hydrophobic characteristics are the two main specifications of the MPL. The effective diffusivity of the MPL is a key property in determining the fuel cell performance. However, since the MPL is a recently developed material, the number of published works with focus on its diffusivity is limited. Measuring the MPL diffusivity is a challenging task since the MPL needs a physical support and cannot be analyzed as a separate object. Similar to its measurements, modeling the MPL diffusivity is also a difficult task (Nanjundappa et al., Electrochimica Acta 110:349-57), since it involves the reconstruction of the complex structure numerically and solving the diffusion equations in the nano-scale pores where the continuum assumption may be invalid and Knudsen diffusion may prevail. Usually, complex numerical algorithms are employed to reconstruct a small portion of the MPL. This step is followed by a computationally intensive stage to solve the diffusion equations inside the void spaces of the reconstructed domain. Although this approach leads to reliable and accurate results, an analytical relationship that correlates certain design parameters to the MPL diffusivity could be helpful. A fully analytical solution of the mass transport equation inside a randomly structured porous material is however not feasible. Simplifying assumptions are therefore required to derive an analytical model for predicting the transport properties of porous structures. The unit cell approach is one way of simplifying the structure. A unit cell is a hypothetical, periodic domain that represents the entire structure. Hence, optical observations can aid the selection of the optimal unit cell arrangement. In this work a unit cell is chosen based on cross-sectional SEM images of a standard MPL material. Generally, two main regions can be observed in the MPL: i) clusters of spherical particles; and ii) pores. The considered unit cell, which is devised based on these observations, is shown in Figure 1. The analogy between the heat and mass transfer is employed to solve the diffusion equation in the unit cell and a relationship is proposed to calculate the effective MPL diffusivity. The obtained values from this relationship are compared with the experimental data available in the literature and another stochastic model which is under development in our group. The proposed relationship is able to predict the MPL diffusivity with an acceptable accuracy, i.e., with less than 10% deviation. The required input parameters of the model are particle diameter, MPL porosity, and average pore size. A parametric study is then performed to examine the effects of these parameters on the MPL diffusivity. The proposed relationship is expected to be useful to the fuel cell community, especially for the purposes of performance modeling. Furthermore, the results from the parametric study c provide valuable information on the effects of carbon particle size, the MPL porosity, and the MPL pore size distribution on its effective diffusivity. Acknowledgments:This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada.

The Effect of Carbon Particle-Size on N-Doped Carbon Catalyst for Oxygen Reduction Reaction in Microbial Fuel Cells

Microbial fuel cell (MFC) is a new technology that combines wastewater treatment and bioenergy production. Platinum, as a commonly used catalyst for oxygen reduction reaction (ORR) in MFC, has hindered the development of MFC as the result of its high-cost. Consequently, developing effective and low-cost catalysts for ORR has aroused extensive research interest. The particle size effect is known to play an important role for catalyst. Three kinds of carbon powders with different grain sizes were chosen to prepare nitrogen-doped carbon powder (NDCP) as a low-cost catalyst for oxygen reduction in MFCs. The result showed that particle-size effect might be attributed to morphological changes of the relative concentration of surface atoms and nitrogen functional groups. As a result, the power density of NDCP with carbon 8000 mesh (739.2 mW m-2) was much higher than another two catalysts by 40% (carbon 10000 mesh, 413.1 mW m-2) and 60% (carbon 3000 mesh, 248.5 mW m-2). In addition, carbon 8000 mesh exhibited a bit higher coulombic efficiency than carbon 10000 mesh and carbon 3000 mesh.

Effect of Carbon Particle Size on Electrochemical Performance of EDLC

The effect of particle size on the electrochemical performance of electrical double-layer capacitors (EDLCs) has been studied using carbon derived from silicon carbide powders with to grains at temperatures from 800 to . For the same synthesis temperature, similar pore texture and microstructure of carbide-derived carbons produced from different powders have been observed. Nanoparticles exhibited a slight porosity modification with a larger pore volume and surface area as compared to micrometer particles ( and ). Capacitances as high as associated with a small resistance and time constant have been reached for nano- and sub-micrometer particles synthesized at low temperatures and tested in a tetraethylammonium tetrafluoroborate in acetonitrile solution. This result suggests that small particles facilitate the migration of the ions inside the porous electrodes, allowing them to reach the whole pore volume due to a shorter transport distance within the particle.

The role of particle size on the deposition efficiency of ink on plastic spheres

Abstract Experimental investigation of the effect of carbon particle size on its deposition efficiency on the surface of plastic particles has been performed in stirred vessel. A model based on Langmuir kinetics was used, and it provided a good fit for the experimental results. The effect of de-inking conditions such as, carbon particle size, calcium chloride concentration, and carbon concentration has been investigated. Different sizes of carbon particles were tested. It was found that the deposition rate and the deposition efficiency were generally higher for the larger carbon particles. The effect of CaCl 2 concentration on the deposition efficiency was investigated. Results showed that the deposition rate increased when the concentration of CaCl 2 increased from 0.05 to 0.10 g/l (the stochiometric ratio needed to react with sodium stearate). Moreover, the deposition efficiency was higher at this concentration. Concentrations above the stochiometric ratio did not show a systematic behavior for the deposition rate and the deposition efficiency. Finally, the effect of carbon concentration was examined. Carbon concentration of 0.25, 0.30, and 0.40 g/l were used. Results showed that the concentration of carbon did not affect the deposition efficiency nor the rate of deposition. This study confirmed the applicability of the method of ink removal from recycled waste paper using plastic particles, proposed by previous investigators.

Mechanical and dielectric properties of styrene-butadiene rubber polyester short-fiber composites, part III: Composites loaded with fast extrusion furnace carbon black

The present article aims to study the mechanical and dielectric properties of styrene butadiene rubber (SBR) reinforced with polyester (PE) short-fiber loaded with fast extrusion furnace carbon black (FEF) in increasing quantities. The effect of carbon particle size on the mentioned properties is also reported. From the results obtained in this article and others, it was found that, the tensile strength and Young's modulus of FEF and HAF carbon black increase with the increase of carbon content whereas elongation at break was decreased. The retaining ability of the tensile strength and Young's modulus of the composites loaded with either FEF or HAF carbon black has been increased with the increase of aging time and decreased by increasing carbon content in the vulcanizates. At certain concentration of carbon black in the rubber matrix, there was an abrupt increase in the dielectric permittively l ' and the dielectric loss l ". The concentration at which l ' and k " shows a sharp increase is in line with the increase of carbon black particle size. The mechanical and dielectric properties for vulcanizates loaded with smaller carbon black particle size are higher than those loaded with larger ones. The dielectric permittivity l ' has been increased by increasing the temperature whereas the dielectric loss was decreased. The results are discussed and Interpreted.

Water purification by radiation induced oxidation (thesis excerpts)

Abstract Water can be purified using carbon adsorption with subsequent γ‐radiation induced oxidation of the adsorbates. A theoretical design model of formaldehyde removal and destruction is presented. Results from this computer simulation are compared to experimental data. A kinetic model is proposed for the surface mechanisms which are patterned after those reactions known to occur in the aqueous phase. Maintaining a high oxygen partial pressure is a key design consideration. Simulations from 1–10 atm pressure suggest that pressurized operation will significantly enhance the oxidation rates. Other key physical parameters are the external and pore diffusion rates to the solid surface, oxygen adsorption, and the effects of carbon particle size. Three γ‐radiation sources were examined: 137Cs pollucite in the standard Hanford capsule, 60Co, and spend light water reactor (LWR) fuel rods. Cobalt‐60 offers the highest radiation intensity and efficiency, but it is also the most expensive radiation source.

The kinetics of reduction of hematite by carbon

Reduction kinetics of mixtures of hematite and carbon powders were investigated in the temperature range of 850° to 1087°C. Experiments were carried out under argon atmosphere and the isothermal weight loss of the samples was determined as a function of time. The effects of carbon particle size, hematite/carbon ratio of the mixture, and addition of promotive or inhibitive reagents were also investigated. The results were summarized in the form of fractional reaction vs time plots. A kinetic model developed on the basis of carbon solution-loss reaction as rate-controlling represented the results fairly well. An enthalpy of activation of 72 kcal/per mole was calculated, within the range of 957° to 1087°C. The observed effects of Li2O and FeS on the reduction kinetics are consistent with the influence these reagents are known to exercise on the solution-loss reaction.