Graphite Cylinder Research Articles

The Calculation of Double Nonlinearity and Material Anisotropy Influence on the Temperature Distribution in the Cylinder Under High Temperature Heat Exchange

At the present stage of the development of technology, it is necessary to ensure the strength, reliability and durability of the structure that successfully functions under conditions of high-temperature heat exchange as maximum as possible. In this regard, graphite structural elements are widely used, and they are also applied for parts of space and aircraft, jet and rocket engines. The transversely isotropic graphite cylinder used in this work has a unique set of qualities that make it indispensable for problems in nuclear physics and power engineering; however, in the calculation of thermal engineering practice, it has not been studied enough, since it contains a large scatter of thermophysical characteristics for various grades of graphite. The aim of the study, including the basis of the developed method for solving boundary value problems of doubly nonlinear unsteady thermal conductivity, is to consider the effect of temperature dependences of the thermophysical characteristics of the material on temperature, zonal radiative-convective heat transfer and anisotropy on the distribution of temperature fields along the length, at the center and surface of a semi-infinite solid cylinder. The essence of this method is that the Goodman’s and Kirchhoff’s transformations are applied to the problem posed converted to a dimensionless form, then the relative temperature and functions from it, are expanded in the series of sines on the a priori interval, then the superposition principle is applied, after which the original setting is converted to a set of linearized problems with reduced thermophysical characteristics. Linear problems are solved by the method of integral transformations, which are summed up. The upper limit of the priori interval is determined from the condition that the relative temperature obtained from the solution of the problem Fo ® ¥ takes the value of the upper limit of the a priori interval. A large number of numerical calculations in the Matlab environment graphically show changes in the relative temperature on the axis and surface of the cylinder in a wide range of Fourier criteria. It is found that with an increase in the Fourier criterion, the character of heating changes qualitatively from the axis to the surface of the cylinder, both in terms of nonlinearities and anisotropy. For the case of double nonlinearity, the location of the temperature fields at different anisotropies in comparison with an isotropic material is shown graphically.

Efficient dairy wastewater treatment and power production using graphite cylinders electrodes as a biofilter in microbial fuel cell

The goal of this work was to evaluate the efficiency of an air-cathode microbial fuel cell (MFC), operating in semi-continuous downflow mode. The MFC was inoculated with a consortium of Shewanella oneidensis and Clostridium butyricum. It was fed using a synthetic medium with progressively increasing dairy wastewater (DWW) concentrations in the startup (15 days), acclimatization (30 days), and treatment (75 days) phases. This approach enabled removal of 89% of the total COD and 91% of the total BOD, after 90 days of operation. These efficiencies were improved with step change of external resistance (Rext.) from 1.0 to 0.5 kΩ. Electrochemical impedance spectroscopy analysis indicated the formation of more complex biointerface associated with change of Rext. The maximum power density was 3.5 W∙m−3 at 1.0 A∙m−3, during the startup, while the Coulombic efficiency (CE) was 4.5 at the end of the operation. The MFC process showed high efficiency for the removal of organic nitrogen (85%), phosphorus (92%), nitrate (100%), and sulfate (88%). Additionally, the treated DWW effluent presented no acute toxic effect towards Daphnia similis. Overall, it could be concluded that applying gradual increments of the DWW concentration resulted in highly efficient treatment.

Removal of reactive red 195 from dyeing wastewater using electro-Fenton process in a cell with oxygen sparged fixed bed electrodes

This research focuses on the use of electro-Fenton processes for degradation of reactive red 195, the degradation is achieved by reactions with hydroxyl radicals (O˙H) which are produced from Fenton reaction using a new O2 sparged electrochemical reactor consisting of fixed bed cathode made of carbon cylinders and a horizontal array of closely packed steel screens anode. Variables studied were current density, initial dye concentration, oxygen superficial velocity, and number of graphite layers (bed thickness). Color removal efficiency reached 100 % and chemical oxygen demand (COD) removal reached 96 % for the dye initial concentration of 50 ppm at current density =2 mA/cm2, superficial oxygen velocity =0.012 cm/s, 60 miutes contact time, a cell with a three layer of graphite cylinders fixed bed cathode was used. Under these conditions, the energy consumption was found to be 17 kW⋅h/kg of removed dye, and the electrical cost of dye removal ≈ 0.85 $/ kg dye removed. Kinetics study revealed that dye removal takes place through a first-order reaction. The merits of the present reactor compared to the reactors used in previous studies were highlighted.

Effect of the presence of solid particles, on the vanadyl sulfate (VOSO4) oxidation current

This study considers the effect of mechanical stirring of V(IV) solutions and of the presence of solid suspensions on the VO(aq)2+ oxidation current measured on a graphite electrode, with the objective of a better understanding of the electrochemical reactions taking place in a vanadium redox flow battery (VRFB). Our research question was to determine whether the presence of different kind of solid particles (inert glass spheres, VOSO4 powder and nanometric ketjen black (KB)) could be beneficial to the electrochemical performances of the VRFB. The experimental method consisted in measuring the anodic limiting current of a VOSO4-H2SO4-H2O solution on a rotating graphite cylinder, by linear sweep voltammetry.In the absence of solid particles, we show that the mass transfer coefficient dependence against the angular velocity of both the electrode and an additional stirrer obey to a power law (k = f(ωγ)) with an exponent γ found to be lower than the theoretical value. The beneficial effect on the mass transfer of VO2+ at the interface observed with low fraction of inert glass particles dramatically disappears as the spheres fraction increases. This is attributed to the decrease of the available free volume for the diffusion. When the solid consists of VOSO4 particles, the anodic current decreases as the mass fraction of the solid increases, which demonstrates the absence of any significant beneficial effect of the dissolution of the VOSO4 grains in the diffusion layer. Conversely, an important increase (~ 40%) of the oxidation current is observed when KB particles were introduced at low fractions (0.15%) in the bulk, thanks to the electronic percolation created by the KB. However, this beneficial effect disappears for higher mass fraction of both vanadium or KB solid particles, because of the destruction of the aggregates enabling the electron to be driven into the bulk.

Lifetime Prediction for Structural Elements of a Tamman Vacuum High-Temperature Furnace by Means of Mathematical Models

A mathematical structural model of a Tamman vacuum high-temperature electric furnace with a heater in the form of a coal or graphite pipe and thermal insulation in the form of graphite cylinder shields is developed and implemented in the Simulink software package. The thermal resistance of the thermal conductivity of graphite shields, which is traditionally neglected in the calculation of widespread thin metal shields, was taken into account in the simulation of thermal processes. Also, the model takes into account the mass flow of the material of the elements of the furnace structure (the speed of the mass flow depends on the temperature and pressure in the working space), causing a change of the size and, correspondingly, the coefficients of the heat transfer caused by the radiation of the elements of the structure. The temperature regime of separate structural elements (heaters, shields, etc.) is analyzed both for a constant supply voltage of heaters and for the case in which a closed temperature control system is used. The influence of the temperature regime of structural elements on the wear of heating elements and shields is shown.

OA074] Fano theory validation of the MCNP6.0 Monte Carlo code for medical applications

Purpose Fano theory states that charged particle fluence through a medium should be independent of mass density. Therefore, the validity of a Monte Carlo code depends on whether the transport of charged particles complies with this theory. In this work, in the framework of the EMPIR funded RTNORM project, the validity of the Fano theory in the Monte Carlo code MCNP6.0 is tested in a cavity. Methods The methodology used is based on the one performed for the code PENELOPE. Two concentrical cylinders of graphite are created, with the inner one having a density equal to the density of air, and the outer one with the natural density of graphite. A linear source of electrons with energy E 0 is created and the dose in the inner cylinder is determined. The width of the outer cylinder is equal to 1.4* R CSDA . In this setup, the value of: Q = Dose per particle E 0 1 + 2 ρ wall Δ z wall ρ gas Δ z gas should be equal to 1. Dose per particle is determined by means of the tally F6 of the MCNP6.0 code. Default as well as modified physics parameters are used to ascertain limits of the validity. Parameters such as EFAC, ESTEP are changed to verify the changes in the value of Q. Results Results show that if using default physics parameters in the MCNP6.0 code the Fano theory is not verified in the E 0 electron range of 50–200 keV. Conclusions MCNP6.0 has difficulty in tallying energy deposition accurately in a cavity if default physics parameters are used. In this energy range MCNP6.0 presents crossing-boundary artifacts that could probably be due to the use of the condensed-history electron transport Energy Indexing Algorithm (ITS algorithm).

Synthesis and formation mechanism of α-Si3N4 single-crystalline nanowires via direct nitridation of H2-treated SiC fibres

Silicon nitride (Si3N4) nanowires were synthesised using H2-treated SiC fibres as raw materials and a graphite cylinder as the substrate at 1500 °C in N2 atmosphere. The nanowires were characterised by X-ray photoelectron spectroscopy, chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results showed that the Si3N4 nanowires have diameters ranging from a few tens to hundreds of nanometres and lengths of several hundred micrometres. The preferred growth direction of the nanowires was (010), and the nanowires comprised single-crystalline α-Si3N4. In addition, the formation mechanism of Si3N4 nanowires was discussed. The free silicon in the H2-treated SiC fibres was found to react with N2 to form Si3N4 nanowires, leading us to speculate that the growth mechanism involves a vapour-solid process.

Electron cyclotron resonance plasma reactor for production of carbon stripper foil

A graphite antenna for the production of carbon-containing hydrogen plasmas is being developed to prepare impurity-free charge exchange foils for high-energy synchrotrons. Microwave power at 2.45 GHz frequency drives a coaxial structure antenna with a 12-mm-diameter central graphite cylinder and a tapered surrounding cylinder serving as the ground electrode. The antenna was placed in a linear magnetic field to investigate how it performs under an electron cyclotron resonance (ECR) condition. A clear resonance phenomenon was observed in plasma luminosity, microwave power absorption, and microwave power reflection when the induction current used to produce a linear magnetic field was changed. The antenna realized the best microwave coupling to the plasma with the ECR zone formed 5 mm from the end of the center electrode. The antenna realized stable operation for more than 5 h with 100 W input microwave power and with operating hydrogen pressure from 0.5 to 50 Pa.

Impact of gap size uncertainty on calculated temperature uncertainty for the advanced gas reactor experiments

Research being conducted on tristructural-isotropic fuel development and qualification involves seven advanced gas reactor (AGR) experiments that were planned to provide fuel qualification data to support the licensing and operation of the high-temperature gas-cooled reactor. Each AGR test consists of multiple independent capsules containing fuel compacts placed in one or more graphite cylinders shrouded by a stainless-steel shell. These capsules are instrumented with thermocouples embedded in the graphite holder, enabling temperature control. The desired fuel temperature is maintained by variation of the neon/helium gas mixture in response to feedback from thermocouple readings. In the absence of direct measurements, the commercial finite-element heat transfer code ABAQUS was used to predict fuel temperatures. Recognizing inherent uncertainties in the simulation model due to complex physical mechanisms, capsule geometries, and material properties, comprehensive temperature uncertainty quantification was performed. The uncertainty results reveal that the uncertainties in gap sizes are among the most influential factors contributing to calculated temperature uncertainty. The gap size uncertainties originate from a lack of direct experimental data for accurate assessment of dimensional change rates of fuel compacts and graphite components due to complex irradiation-induced material shrinkage or swelling. The study described here focuses on the impact of the gap size uncertainties based on the post-irradiation examination metrology data on calculated temperature uncertainty.

The Characterization of Fibrous Material in CVI Graphite Cylinder Wall

By isothermal chemical vapor infiltration (ICVI) preparation of carbon/carbon composites, We found fibrous materials with silver metallic luster in CVI furnace graphite cylinder outer wall, fiber diameter is 1 ~ 2 mm, length is 4 ~ 15 mm. The characterization of fibrous material have been systematically studied by scanning electron microscopy (SEM),element analysis, energy dispersive X-rays spectroscopy (EDS).After 2300 degrees heat treatment, the fibrous material were characterized by ultra-violet laser Raman spectroscopy. The SEM examination shows that these fibrous materials have a spherical top, the cross-section reveals a unique structure in which layers like growth rings lie concentrically on top of each other. The EDS analysis show the main element of fibrous material is carbon and a small amount of metallic element. Raman spectra show after 2300°C high temperature treatment ,the carbon fibrous material transformed from layer structure to graphite structure.

Benchmarking of HEU mental annuli critical assemblies with internally reflected graphite cylinder

Three experimental configurations of critical assemblies, performed in 1963 at the Oak Ridge Critical Experiment Facility, which are assembled using three different diameter HEU annuli (15-9 inches, 15-7 inches and 13-7 inches) metal annuli with internally reflected graphite cylinder are evaluated and benchmarked. The experimental uncertainties which are 0.00057, 0.00058 and 0.00057 respectively, and biases to the benchmark models which are − 0.00286, − 0.00242 and − 0.00168 respectively, were determined, and the experimental benchmark keff results were obtained for both detailed and simplified models. The calculation results for both detailed and simplified models using MCNP6-1.0 and ENDF/B-VII.1 agree well to the benchmark experimental results within difference less than 0.2%. The benchmarking results were accepted for the inclusion of ICSBEP Handbook.

The problems of piston skirt microgeometry in combustion engines

Geometry of the slot between piston bearing surface and cylinder bore affects the friction losses of the IC engine to the far extent. It appears that these losses depend more on the area covered with oil than the thickness of oil layer separating collaborating parts. Barrel-shaped or stepwise piston bearing surface is the way to reduce the oil covered area. Turns out that the referred to friction losses contributes more to area covered by the oil film than the film thickness of the separation elements cooperating. The method to reduce the area covered by the oil film is a modification of the bearing surface of the piston by adjusting the profile. This paper presents the results of simulation leading to the reduction in friction losses and abrasive wear of piston bearing surface and cylinder bore. Covering the piston bearing surface with a thin layer of graphite one can get an extremely advantageous tribological properties of the piston assembly which means the expected parameters of oil film and in a case of film rupture-an ignorable abrasive wear of the graphite layer and/or cylinder bore.

Mass removal by oxidation and sublimation of porous graphite during fiber laser irradiation

The various effects of laser heating of carbon materials are key to assessing laser weapon effectiveness. Porous graphite plates, cylinders, and cones with densities of 1.55 to 1.82 g/cm3 were irradiated by a 10-kW fiber laser at 0.075 to 3.525 kW/cm2 for 120 s to study mass removal and crater formation. Surface temperatures reached steady state values as high as 3767 K. The total decrease in sample mass ranged from 0.06 to 6.29 g, with crater volumes of 0.52 to 838 mm3, and penetration times for 12.7-mm-thick plates as short as 38 s. Minor contaminants in the graphite samples produced calcium and iron oxide to be redeposited on the graphite surface. Dramatic graphite crystalline structures are also produced at higher laser irradiances. Significantly increased porosity of the sample is observed even outside the laser-irradiated region. Total mass removed increases with deposited laser energy at a rate of 4.83 g/MJ for medium extruded graphite with an apparent threshold of 0.15 MJ. At ∼3.5 kW/cm2, the fractions of the mass removed from the cylindrical samples in the crater, surrounding trench, and outer region of decreased porosity are 38%, 47%, and 15%, respectively. Graphite is particularly resistant to damage by high power lasers. The new understanding of graphite combustion and sublimation during laser irradiation is vital to the more complex behavior of carbon composites.

Measurement of leakage neutron spectra from graphite cylinders irradiated with D-T neutrons for validation of evaluated nuclear data

A benchmark experiment for validation of graphite data evaluated from nuclear data libraries was conducted for 14MeV neutrons irradiated on graphite cylinder samples. The experiments were performed using the benchmark experimental facility at the China Institute of Atomic Energy (CIAE). The leakage neutron spectra from the surface of graphite (Φ13cm×20cm) at 60° and 120° and graphite (Φ13cm×2cm) at 60° were measured by the time-of-flight (TOF) method. The obtained results were compared with the measurements made by the Monte Carlo neutron transport code MCNP-4C with the ENDF/B-VII.1, CENDL-3.1 and JENDL-4.0 libraries. The results obtained from a 20cm-thick sample revealed that the calculation results with CENDL-3.1 and JENDL-4.0 libraries showed good agreements with the experiments conducted in the whole energy region. However, a large discrepancy of approximately 40% was observed below the 3MeV energy region with the ENDF/B-VII.1 library. For the 2cm-thick sample, the calculated results obtained from the abovementioned three libraries could not reproduce the experimental data in the energy range of 5–7MeV. The graphite data in CENDL-3.1 were verified for the first time and were proved to be reliable.

Arc discharge boron nitrogen doping of carbon nanotubes

This article describes the significant roles of process parameters in the deposition of boron and nitrogen co-doped multi-walled carbon nanotubes via the arc-discharge process. The fabrication process is based on the vaporization of solid hexagonal boron nitride embedded in graphite cylinders in a nitrogen atmosphere with pressure varying from 350mbar to 700mbar and controlled current density between 150 and 420A/cm2. Our results show the presence of significant amount of doped boron carbon nitride nanotubes in the cathodic deposit. These nanotubes have a narrow diameter distribution (20–30nm) and a length up to 1μm as analyzed by scanning electron microscopy and transmission electron microscopy. In addition to the experimental study, numerical simulations were performed to determine the temperature and chemical species distributions in the arc plasma under specific boron carbon nitride nanotubes synthesis conditions, thereby providing valuable insight into nanotubes growth and doping mechanisms in the arc.

On-line test using multi-foil SiC target at iThemba LABS

In a collaboration between the INFN-SPES project and iThemba LABS, an on-line test of the power dissipation of a multi-slice target concept for radioactive-ion beam production has been performed. Using the 66MeV proton beam from the iThemba LABS Separated Sector Cyclotron, a total power of 4kW was deposited in the target complex, consisting of 13 Silicon Carbide (SiC) discs of about 1 millimetre thickness housed in a graphite cylinder. The results of the measurements fully validate thermal FEM simulations and confirm that the multi-foil target system is a reliable and affordable device for second-generation ISOL-RIB facilities like SPES.

Analysis of fission gas release-to-birth ratio data from the AGR irradiations

A series of advanced gas reactor (AGR) irradiation tests is being conducted in the advanced test reactor (ATR) at Idaho National Laboratory (INL) in support of development and qualification of tristructural isotropic (TRISO) fuel used in the High temperature gas-cooled reactor (HTGR). Each AGR test consists of multiple independent capsules containing fuel compacts placed in a graphite cylinder shrouded by a steel shell. These capsules are instrumented with thermocouples (TC) embedded in the graphite enabling temperature control. For AGR-1, the first US irradiation of modern TRISO fuel completed in 2009, there were no particle failures detected. For AGR-2, a few exposed kernels existed in the fuel compacts based upon quality control data. For the AGR-3/4 experiment, particle failures in all capsules were expected because of the use of designed-to-fail (DTF) fuel particles whose kernels are identical to the driver fuel kernels and whose coatings are designed to fail under irradiation. The release-rate-to-birth-rate ratio (R/B) for each of krypton and xenon isotopes is calculated from release rates measured by the germanium detectors used in the AGR fission product monitoring (FPM) system installed downstream from each irradiated capsule. Birth rates are calculated based on the fission power in the experiment and fission product generation models. Thus, this R/B is a measure of the ability of fuel particle coating layers and compact matrix to retain fission gas atoms preventing their release into the sweep gas flow. The major factors that govern gaseous diffusion and release processes are found to be fuel material diffusion coefficient, temperature, and isotopic decay constant. To compare the release behavior among the AGR capsules and historic experiments, the R/B per failed particle is used. HTGR designers use this parameter in their fission product behavior models. For the U.S. TRISO fuel, a regression analysis is performed to establish functional relationships between R/B per failed particle of selected noble gas isotopes and temperature. The effect of isotopic half-life is also obtained from the data. To reduce measurement uncertainty of the release rate, the krypton and xenon isotopes selected for regression analysis have a short enough half-life to achieve equilibrium in the capsule, but are also long enough to provide a measurable signal in the FPM detector. The impact of uncertainty of the estimated number of failed particles in each capsule is also examined. This study found that R/B values for AGR test fuel are comparable to R/B obtained in historic tests. The correlation with isotopic half-life is very stable with time indicating no strong influence of burnup on release. The correlation can be used by reactor designers to estimate fission gas release from postulated failed fuel in HTGR cores.

Approximate analytical solution for induction heating of solid cylinders

An approximate solution to the mathematical model for induction heating of a solid cylinder in a cylindrical induction coil is presented here. The coupled multiphysics model includes equations describing the electromagnetic field in the heated object, a heat transfer simulation to determine temperature of the heated object, and an AC circuit simulation of the induction heating power supply. A multiple-scale perturbation method is used to solve the multiphysics model. The approximate analytical solution yields simple closed-form expressions for the electromagnetic field and heat generation rate in the solid cylinder, for the equivalent impedance of the associated tank circuit, and for the frequency response of a variable frequency power supply driving the tank circuit. The solution developed here is validated by comparing predicted power supply frequency to both experimental measurements and calculated values from finite element analysis for heating of graphite cylinders in an induction furnace. The simple expressions from the analytical solution clearly show the functional dependence of the power supply frequency on the material properties of the load and the geometrical characteristics of the furnace installation. The expressions developed here provide physical insight into observations made during load signature analysis of induction heating.

6″ crystalline silicon solar cell with electron-beam melting-based metallurgical route

This paper presents a metallurgical route that consumes much less energy than the gasification route such as Siemens process-based photovoltaic (PV) value chain including metallurgical-grade silicon (MG-Si), solar-grade silicon (SoG-Si) purified by the metallurgical route, Czochralski (Cz) ingot growth, 6″ wafer fabrication, solar cell fabrication, and PV performance evaluation. Mono-like crystalline silicon ingot for achieving high purity was continuously cast with MG-Si for the fabrication of feedstock for Cz ingot growth through the advanced electron beam melting (EBM) system. The system was developed with the combination of vacuum refining part and directional solidification (DS) part for the purification of large amounts of MG-Si, where the two parts are connected by an overflow of Si melts to undergo continuous refining and casting processes in a chamber. To grow the mono-like crystalline Si ingot in our EBM system, a single crystalline seed was placed on the graphite dummy cylinder with DS zone. The mono-like crystalline Si ingot with high purity of >99.999% (above 5N) was blended 50–50 with undoped SoG-Si chunk for the compensation of boron dopant concentration in a crucible of Cz grower. The 156×156mm2 wafers were cut from Cz ingot grown with purity of >99.99999% (above 7N) by slurry-based multi-wire sawing and were fabricated by the conventional solar cell process. The measured photovoltaic performance recorded cell efficiency of 17.1%; hence its higher potential for application to the PV industry.

Polarization dependence of laser interaction with carbon fibers and CFRP

A key factor for laser materials processing is the absorptivity of the material at the laser wavelength, which determines the fraction of the laser energy that is coupled into the material. Based on the Fresnel equations, a theoretical model is used to determine the absorptivity for carbon fiber fabrics and carbon fiber reinforced plastics (CFRP). The surface of each carbon fiber is considered as multiple layers of concentric cylinders of graphite. With this the optical properties of carbon fibers and their composites can be estimated from the well-known optical properties of graphite.