Radial Temperature Profiles Research Articles

Two-dimensional laser-induced fluorescence thermometry in a medium- to high-enthalpy CO2 flow

Ground-based experimental facilities are needed to qualify materials subjected to aerothermodynamic loads during an entry into the Martian atmosphere. In the present work, the focus is on quantifying the temperature field in a medium- to high-enthalpy CO_{2} flow (from 4.5 to {10.5}, hbox {MJ}/hbox {kg}) of a plasma wind tunnel using one- and two-dimensional two-photon absorption laser-induced fluorescence (CO-TALIF) thermometry at a CO number density in the range of 1–2 times 10^{17} cm^{-3}. However, the measurement method developed here can also be used to study satellite propulsion systems. Due to absorption by air, a two-photon excitation scheme of the CO molecule at 115 nm (VUV) was used. Experimental and simulated excitation spectra are compared for temperature determination. For spectrum simulation in the B^1varSigma ^+leftarrow X^1varSigma ^+ system, an existing program was extended and a polynomial regression correlation was developed for signals with low signal-to-noise ratios. After the first one-dimensional temperature measurements using CO-TALIF in the free-stream to quantify the radial temperature profile for three conditions in the medium- to high- enthalpy range, respectively, two-dimensional measurements in a steady state test chamber at room temperature were carried out. For the two-dimensional investigations, a light sheet optic was designed to generate a light sheet free of divergence in width and thickness. The results of the one- and two-dimensional temperature measurements performed at medium- to high-enthalpy conditions provided plausible results concerning both the values and the course in radial and axial direction, the latter being, to the authors’ knowledge, the first two-dimensional temperature measurements under such conditions using CO-TALIF.

Effect of burn-up on the thermal conductivity of light water reactor fuel: Results of investigations employing the laser flash technique

Analysing data drawn from three of EPRI's NFIR Programmes and the High Burn-up Rim Project (HBRP) managed by CRIEPI of Japan, expressions for the degradation of thermal conductivity with burn-up up to 103.5 MWd/kgHM are presented. These indicate that at high burn-up, above 70 MWd/kgHM, the thermal conductivity of the matrix of the high burn-up structure (HBS) increases by 25 - 30% concomitant with recrystallization of the fuel grains. This increase is partially or completely off-set, however, by a decrease in conductivity associated with the porosity of the HBS which contains the fission gas gathered from the fuel matrix during transformation of the microstructure. Below 70 MWd/kgHM, in the absence of the HBS, the conductivity is about 15% lower than that currently accepted. It is also found that the conductivity of UO2 fuel falls sharply immediately when irradiation begins. This is attributed to radiation damage rather than the incorporation of fission products in the fuel lattice. The data further reveal that at burn-ups below 70 MWd/kgHM the conductivity of UO2 containing 10 wt% Gd2O3 is markedly lower than that of UO2, but once the HBS has formed its conductivity is indistinguishable from that of conventional UO2, UO2 additive fuel or MOX. It is concluded that for accurate determination of the radial temperature profile in a high burn-up fuel pellet, knowledge of the volume fraction of the HBS in the pellet and the radial distribution of the porosity in the affected region is required.

Numerical analysis of multi-regime combustion using flamelet generated manifolds - a highly-resolved Large-Eddy Simulation of the Darmstadt multi-regime burner

Multi-regime effects occur due to the interaction of combustion phenomena such as partial premixing of reactants or product-recirculation and lead to the invalidity of idealization of local reaction zones by purely premixed or purely non-premixed flame structures. The recently proposed multi-regime burner (MRB) at the Hochschule Darmstadt and the TU Darmstadt is investigated using highly-resolved Large-Eddy Simulation (LES) regarding the present combustion modes – with focus on MILD combustion – and overall flame characteristics. Thermochemical experimental data and highly resolved LES are compared for two selected operating conditions MRB18b and MRB26b. The experimental investigation focuses on the overall flame structure by examining radial profiles of temperature and mixture fraction, as well as scatter plots of temperature and CH4 versus mixture fraction. The objective of this analysis is to provide insights into the reaction zone structure which are difficult to extract by experimental means, by using highly-resolved Large-Eddy Simulations under flow conditions representative of MRB18b and MRB26b. The generated database was used to allow for a separate analysis of the inner and outer flame branches. SO2 measurements were analyzed together with the simulated temperature fields to further assess the flame stabilization mechanism in this configuration. The importance of different flame zones and burning modes was analyzed using the flame index and temperature locus diagrams. The effects of the flame zones are found to evolve with the downstream distance and show distinct differences between the two operating conditions. The applied diagnostics reveal the spatial and thermodynamical state of the different regimes.

Helios 2 observations of solar wind turbulence decay in the inner heliosphere

Aims. A linear scaling of the mixed third-order moment of the magnetohydrodynamic (MHD) fluctuations is used to estimate the energy transfer rate of the turbulent cascade in the expanding solar wind. Methods. In 1976, the Helios 2 spacecraft measured three samples of fast solar wind originating from the same coronal hole, at different distances from the Sun. Along with the adjacent slow solar wind streams, these intervals represent a unique database for studying the radial evolution of turbulence in samples of undisturbed solar wind. A set of direct numerical simulations of the MHD equations performed with the Lattice-Boltzmann code FLAME was also used for interpretation. Results. We show that the turbulence energy transfer rate decays approximately as a power law of the distance and that both the amplitude and decay law correspond to the observed radial temperature profile in the fast wind case. Results from MHD numerical simulations of decaying MHD turbulence show a similar trend for the total dissipation, suggesting an interpretation of the observed dynamics in terms of decaying turbulence and that multi-spacecraft studies of the solar wind radial evolution may help clarify the nature of the evolution of the turbulent fluctuations in the ecliptic solar wind.

A methodology for the analysis of distillation processes within rotating packed beds based on local temperature measurements

A temperature-based measurement methodology for the investigation of the local separation efficiency within the packing of Rotating Packed Beds (RPB) has been developed, which enables the derivation of design criteria and optimal operating conditions. Key therein is the acquisition of experimental data providing a local resolution of the temperature profile within the packing. For this purpose, independent data loggers were adapted and installed to capture radial temperature profiles for the distillation of the binary mixture ethanol and 1-propanol. Based on the positions of the sensors, local separation efficiencies and mass transfer coefficients were determined experimentally. Effects on the analysis due to maldistribution were analysed by deploying variations in packing arrangement. By dividing the packing into different sections and averaging the performance indices, the impact of maldistributions is then compensated. This yields in consistent and reproducible results, showing a decrease in mass transfer rates with increasing radial position and a general enhancement of mass transfer by rotational speed. To our knowledge, this is the first experimental study providing radial temperature profiles for RPBs for varying rotational speeds and a methodology for its analysis.

Numerical Simulation of Wall Condensation from a Superheated Steam and Air Mixture in a Vertical Pipe

The objective of this study was to evaluate the effects of superheat on wall condensation from a steam and air mixture. We previously measured the radial and axial temperature profiles of a superheated steam-air mixture in a vertical pipe with a diameter of 49.5 mm and a cooling height of 610 mm. In this study, we carried out a numerical simulation for the previous measurements by using the computational fluid dynamics (CFD) code FLUENT, and evaluated the profiles of the mixture temperature Tg and steam mass fraction Xs. The profiles of Tg and the saturated temperature Ts obtained from Xs agreed well with those measured with superheated and saturated conditions, respectively. The validity of the correlation to evaluate a condensation heat flux qc (which was based on the gradient of Xs) was confirmed. Profiles of the dimensionless velocity u+, temperature T+, and steam mass fraction Ys + were obtained, and they were compared with wall functions (i.e., the linear function for a viscous sublayer and the logarithmic law for a turbulent layer). The computed profile agreed with the wall function for u+, agreed relatively well with the wall function for T+, and agreed well with the correlation for Ys + obtained from data measured with saturated steam-air conditions in the region of the turbulent layer.

High resolution Thomson scattering diagnostic for measurements of radial profiles of electron temperature and density in the gas dynamic trap.

The incoherent Thomson scattering diagnostic with multiple lines of sight is installed at the gas dynamic trap (GDT) for measurements of radial profiles of the plasma electron temperature and density. The diagnostic is built on the Nd:YAG laser operating at 1064nm. The laser input beamline is provided with an automatic system for alignment status monitoring and correction. The collecting lens uses ∼90° scattering geometry having 11 lines of sight in total. Presently, six of them (covering the full plasma radius from the axis to the limiter) are equipped with high etendue (f/2.4) interference filter spectrometers. The design of the spectrometer's data acquisition system based on the "time stretch" principle allowed for the 12 bits vertical resolution with a sampling rate of 5 GSample/s and a maximum sustainable measurement repetition frequency of 40kHz. The repetition frequency is the crucial parameter for the study of plasma dynamics with a new pulse burst laser to be started in early 2023. Results of the diagnostic operation in several GDT campaigns show that radial profiles are routinely delivered with the typical observation error of 2%-3% for Te ⩾ 20eV in a single pulse. After Raman scattering calibration, the diagnostic is capable to measure the electron density profile with the resolution ne (min)≃4⋅1018m-3 and error bars of 5%.

Study of the Perturbation in Temperature Profile of an AGR Fuel Pin for Surface Roughness of Cladding by CFD Simulation in Ansys Fluent

The surface roughness of nuclear fuel cladding plays a crucial role in the thermal-hydraulic response of the Advanced Gas Cooled reactor (AGR). In the present work, the change in the temperature distribution from an isolated AGR fuel rod to primary coolant due to cladding roughness was studied by computational fluid dynamics (CFD) simulation in Ansys Fluent software. Square transverse ribs of the various pitch to height ratios _p / k_ were considered as the surface roughness. Radial temperature profiles from fuel to coolant were generated. Lower fuel temperature was found for the fuel rod with a rough cladding surface as compared to the smooth cladding surface. The peak fuel temperature was determined and found to decrease with decreasing values of _p / k_ . Temperature drop across the fuel and from fuel to coolant was also studied. DUJASE Vol. 7(1) 9-15, 2022 (January)

Numerical and Chemical Kinetic Analyses on the Formation of CO and CO2 for C1–C4 Hydrocarbon Alkanes in a Hot Co-Flow under MILD Combustion

In this present study, computational fluid dynamics and chemical kinetic analysis are conducted to explore the formation of CO and CO2 for a fuel jet comprising C1–C4 hydrocarbon alkanes in a hot co-flow burner under a moderate or intense low-oxygen dilution (MILD) combustion environment. The fuel jet comprises three cases of fuel mixture (case 1: CH4 + H2, case 2: C3H8 + H2, and case 3: C4H10 + H2) having constant mixture density and operating under a fixed jet Reynolds number. The combustion and emission characteristics are analyzed in terms of radial profiles of temperature and mass fraction of OH, CH2O, HCO, CO, CO2, and C2H2 in the MILD combustion region. The formations of CO and CO2 are examined with the help of reacting flow analysis using the computational fluid dynamics (CFD) tool. The formation of CO is reported as maximum for case 3 and minimum for case 1. However, the reverse trend is observed in the case of CO2 formation. The reacting flow analysis from the CFD work suggests that the reaction C2H2 + O = CH2 + CO strongly influences CO formation in all three fuel mixtures cases. In the current study, acetylene is found to be the primary species that affects the CO formation in the adopted fuel mixtures and is mainly responsible for the increased CO concentration in case 3. Likewise, the formation of CO2 is majorly influenced by the reaction CO + OH = CO2 + H. The reacting flow analysis is assisted with the help of a zero-dimensional perfectly stirred reactor (PSR) model to elucidate the underlying chemistry and explore the significant reaction pathways influencing the formation of CO and CO2. The ethylene route in the reaction pathway substantially plays a vital role in the CO formation in all three fuel mixtures.

Gas clumping in the outskirts of galaxy clusters, an assessment of the sensitivity ofSTAR-X

AbstractIn the outskirts of galaxy clusters, entropy profiles measured from X-ray observations of the hot intracluster medium (ICM) drops off unexpectedly. One possible explanation for this effect is gas clumping, where pockets of cooler and denser structures within the ICM are present. Current observatories are unable to directly detect these hypothetical gas clumps. One of the science drivers of the proposed STAR-X observatory is to resolve these or similar structures. Its high spatial resolution, large effective area, and low instrumental background make STAR-X ideal for directly detecting and characterizing clumps and diffuse emission in cluster outskirts. The aim of this work is to simulate observations of clumping in clusters to determine how well STAR-X will be able to detect clumps, as well as what clumping properties reproduce observed entropy profiles. This is achieved by using yt, pyXSIM, SOXS, and other tools to inject ideally modelled clumps into 3D models derived from actual clusters using their observed profiles from other X-ray missions. Radial temperature and surface brightness profiles are then extracted from mock observations using concentric annuli. We find that in simulated observations for STAR-X, a parameter space of clump properties exists where gas clumps can be successfully identified using wavdetect and masked, and are able to recover the true cluster profiles. This demonstrates that STAR-X could be capable of detecting substructure in the outskirts of nearby clusters and that the properties of both the outskirts and the clumps will be revealed.

The cosmic shallows – I. Interaction of CMB photons in extended galaxy haloes

ABSTRACT We report and analyse a serendipitous finding of foregrounds in the cosmic microwave background (CMB) radiation associated with extended galactic haloes. Using the cross-correlation of Planck and Wilkinson Microwave Anisotropy Probe maps and the 2MRS galaxy catalogue, we find that the mean temperature radial profiles around nearby galaxies at $cz\le 4500~\rm {km~s^{-1}}$ show a statistically significant systematic decrease of $\sim 15~\mu \rm {K}$ extending up to several galaxy radii. This deficit in the temperature strongly depends on the galaxy morphological type at scales within several tens of times the galaxy size, becoming nearly independent of galaxy morphology at larger scales. The effect is significantly stronger for the more extended galaxies, with galaxy clustering having a large impact on the results. Our findings indicate the presence of statistically relevant foregrounds in the CMB maps that should be considered in detailed cosmological studies. Besides, we argue that these can be used to explore the intergalactic medium surrounding bright late-type galaxies and allow for diverse astrophysical analyses.

Shock-wave heating mechanism of the distant solar wind: Explanation of Voyager-2 data

Aims. One of the important discoveries made by Voyager-2 is the nonadiabatic radial profile of the solar wind proton temperature. This phenomenon has been studied for several decades. The dissipation of turbulence energy has been proposed as the main physical process responsible for the temperature profile. The turbulence is both convected with the solar wind and originated in the solar wind by the compressions and shears in the flows and by pick-up ions. The compression source of the solar wind heating in the outer heliosphere appears due to shock waves, which originated either in the solar corona or in the solar wind itself. The goal of this work is to demonstrate that the shock-wave heating itself is enough to explain the temperature profile obtained by Voyager-2. Methods. The effect of shock-wave heating is demonstrated in the frame of a very simple spherically symmetric high-resolution (in both space and time) gas-dynamical data-driven solar wind model. This data-driven model employs the solar-wind parameters at 1 AU with minute resolution. The data are taken from the NASA OMNIWeb database. It is important to underline that (1) the model captures the shocks traveling and/or originating in the solar wind, and (2) other sources of heating are not taken into account in the model. We extended this simple model to the magnetohydrodynamic (MHD) and two-component models and found very similar results. Results. The results of the numerical modeling with the one-minute OMNI data as the boundary condition show very good agreement with the solar-wind temperature profiles obtained by Voyager-2. It is also noteworthy that the numerical results with daily averaged OMNI data show a very similar temperature profile, while the numerical runs with 27-day-averaged OMNI data demonstrate the adiabatic behavior of the temperature.

Thermocouple-based thermometry for laminar sooting flames: Implementation of a fast and simple methodology

This work reports the implementation and the validation of the extrapolation method for thermocouple temperature measurements corrected from the radiation losses in sooting flames. This simple method relies on the use of thermocouples having different size diameters and enables a fast and direct determination of the flame temperature by extrapolation to zero diameter. We propose here a detailed study of the possibilities and limitations offered by this method based on experimental measurements and comparison with well-established methods carried out in a laminar diffusion sooting flame. In details, a specific fast insertion setup using four different sized thermocouples has been implemented to record temperature values at different heights in the flame. From these data, we highlight that a linear calibration curve correlates the raw measured temperatures to the flame temperatures corrected of the radiation losses can be easily and rapidly obtained. The impact of soot deposition on the thermocouple on the temperature measurement is also discussed. To assess the reported thermocouple methodology, a direct comparison is made between the temperature profile determined along the vertical central axis of the flame by the extrapolation method with OH and NO LIF thermometry measurements as well as numerical simulation. Finally, we also report the comparison of experimental and simulated radial temperature profiles highlighting the adequate dynamic of the method for temperature profile determination in high temperature gradient conditions (500 K/mm). This work demonstrates that the extrapolation method is an efficient and fast method to determine accurate temperature profiles in flames, even in presence of soot particles up to a few hundred ppb, which can be useful for the development of fast and cheap sensors for either laboratory or larger-scale applications.

Vertically extended and asymmetric CN emission in the Elias 2-27 protoplanetary disk

Context. Cyanide (CN) emission is expected to originate in the upper layers of protoplanetary disks, tracing UV-irradiated regions. This hypothesis, however, has been observationally tested only in a handful of disks. Elias 2-27 is a young star that hosts an extended, bright, and inclined disk of dust and gas. The inclination and extreme flaring of the disk make Elias 2-27 an ideal target to study the vertical distribution of molecules, particularly CN. Aims. Our aim is to directly trace the emission of CN in the disk around Elias 2-27 and compare it to previously published CO isotopolog data of the system. The two tracers can be combined and used to constrain the physical and chemical properties of the disk. Through this analysis we can test model predictions of CN emission and compare observations of CN in other objects to the massive, highly flared, asymmetric, and likely gravitationally unstable protoplanetary disk around Elias 2-27. Methods. We analyzed CN N = 3–2 emission in two different transitions J = 7/2–5/2 and J = 5/2–3/2, for which we detect two hyperfine group transitions. The vertical location of CN emission was traced directly from the channel maps, following geometrical methods that had been previously used to analyze the CO emission of Elias 2-27. Simple analytical models were used to parameterize the vertical profile of each molecule and study the extent of each tracer. From the radial intensity profiles we computed radial profiles of column density and optical depth. Results. We show that the vertical location of CN and CO isotopologs in Elias 2-27 is layered and consistent with predictions from thermochemical models. A north-south asymmetry in the radial extent of the CN emission is detected, which is likely due to shadowing on the north side of the disk. Combining the information from the peak brightness temperature and vertical structure radial profiles, we find that the CN emission is mostly optically thin and constrained vertically to a thin slab at z/r ~ 0.5. A column density of 1014 cm−2 is measured in the inner disk, which for the north side decreases to 1012 cm−2 and for the south side to 1013 cm−2 in the outer regions. Conclusions. In Elias 2-27, CN traces a vertically elevated region above the midplane, very similar to that traced by 12CO. The inferred CN column densities, low optical depth (τ ≤ 1), and location near the disk surface are consistent with thermo-chemical disk models in which CN formation is initiated by the reaction of N with UV-pumped H2. The observed north–south asymmetry may be caused by either ongoing infall or by a warped inner disk. This study highlights the importance of tracing the vertical location of various molecules to constrain the disk physical conditions.

Two dimensional temperature distributions in a ceiling jet generated by a finite line-source fire: An experimental study

The temperature distributions of ceiling jets are fundamental characteristics in enclosure fire dynamics. It is also the basics in the designs of fire safety devices in buildings, like detection, sprinkler, smoke control and standard fire protection. However, the only exists equation is for the radial ceiling jet temperature profile induced by a point source. There are no studies on line source despite the fact that the non-axisymmetric sources are the more common fires in buildings. This paper, for the first time, investigates the temperature profiles in ceiling jet induced by a finite line-source fire plume impinging upon an unconfined ceiling. Experiments are carried out with a buoyant jet fire and a pool fire. The temperature profile under the ceiling was measured along with flow condition visualized by a laser sheet. It is found that the temperature profile is two-dimensional and decays slower in the y-direction (perpendicular to line source longer side) than that in the x-direction (parallel to line source longer side). The characteristic length scales for characterizing the temperature profiles in the two directions are then proposed on the basis of the dimensions of the plume impinging zone. An equation is derived to describe the two-dimensional temperature profile based on the characteristic length scales. The present study provides basic data and a new equation for temperature profiles of ceiling jet induced by finite line-sources for building fire science.

X-ray illuminated accretion discs and quasar microlensing disc sizes

Aims. We study the half-light radius versus black hole mass as well as the luminosity versus black hole mass relations in active galactic nuclei (AGN) when the disc is illuminated by the X-ray corona. Methods. We used KYNSED, a recently developed spectral model for studying broadband spectral energy distribution in AGN. We considered non-illuminated Novikov-Thorne discs and X-ray illuminated discs based on a Novikov-Thorne temperature radial profile. We also considered the case where the temperature profile is modified by a colour-correction factor. In the case of X-ray illumination, we assumed that the X-ray luminosity is equal to the accretion power that is dissipated to the disc below a transition radius and we computed the half-light radius and the disc luminosity for many black hole masses, as well as a wide range of accretion rates, black hole spins, X-ray luminosities and heights of the corona. Results. The half-light radius of X-ray illuminated radii can be up to ∼3.5 times greater than the radius of a standard disc, even for a non-spinning black hole, based on a wide range of model parameters – as long as the transition radius is larger than three times the radius of the innermost stable circular orbit and the coronal height is greater than ∼40 Rg. This result is due to the fact that the absorbed X-rays act as a secondary source of energy, increasing the disc temperature, and mainly at large radii. Non-illuminated discs are consistent with observations, but only at the 2.5σ level. On the other hand, X-ray illuminated discs can explain both the half-light radius-black hole mass as well as the luminosity-black hole mass relation in AGN, for a wide range of physical parameters. The range of the parameter space is broader in the case where we consider the colour-correction factor. X-ray illuminated discs can explain the data when we observe gravitationally lensed quasars mainly face-on, but also if the mean inclination angle is 60°. In addition, we show that the observed X-ray luminosity of the gravitationally lensed quasars is fully consistent with the X-ray luminosity that is necessary for heating the disc. Conclusions. X-ray disc illumination was proposed many years ago to explain various features that are commonly observed in the X-ray spectra of AGN. Recently, we showed that X-ray illumination of the accretion disc can also explain the observed UV/optical time-lags in AGN, while in this work, we show that the same model can also account for the quasar micro-lensing disc size problem. These results support the hypothesis of the disc X-ray illumination in AGN.

Applications of solar radiation toward the slip flow of a non‐Newtonian viscoelastic hybrid nanofluid over a rotating disk

AbstractThis work explores a semi‐analytical solution of the Magnetohydrodynamics (MHD) viscoelastic water‐based hybrid nanoliquid flow containing TiO2 and CoFe2O4 nanoparticles past a rotating disk along with velocity slip condition. The impact of solar radiation is incorporated in the temperature equation. The current study consists of non‐Newtonian viscoelastic hybrid nanofluid flow problem which is comprised of momentum and temperature equations. By using suitable similarity transformations, the higher‐order nonlinear ordinary differential equations are transformed into the nonlinear ordinary differential equations and then resolved with the execution of the homotopy analysis scheme in MATHEMATICA 10.0. The behavior of the involved physical parameters on the hybrid nanoliquid radial and tangential velocities and temperature profiles are calculated in a graphical form. Also, the skin friction and Nusselt number for /water nanoliquid are described in tabular form. Some major results related to the current work are that by rising the values of the viscoelastic parameter, nanoparticle volume fraction of the titanium dioxide and cobalt oxide increases the skin friction coefficient . The viscoelastic parameter, nanoparticles volume fraction of the cobalt oxide and magnetic parameter reduced the skin friction coefficient of the hybrid nanofluid. It is noted that Nusselt number is lower for both and cases against the absorption factor. The expansion in hybrid nanofluid temperature is examined for both and cases. It is obtained that the temperature and heat rate transfer of the hybrid nanofluid are dominant in the presence of solar radiation.

Fuel-lean ammonia/biogas combustion characteristics under the reacting swirl flow conditions

Ammonia has been identified as a viable energy vector for power generation. Using dual-fuel operation that mixes the ammonia with higher reactivity gaseous fuel can be vital in enhancing ammonia combustion. This study examined the fundamental swirl combustion characteristics of fuel-lean premixed ammonia/biogas via a numerical approach. The flame was established at an input thermal power of 7 kW and a global equivalence ratio of 0.8. The numerical model was validated with biogas emissions data acquired through experimental work. At 20 mm downstream the burner, increased carbon dioxide mass fraction in the biogas lowered the peak flame temperature by around 300 K. Moreover, the deformation of flame temperature radial profiles was also found aggravated as carbon dioxide concentration in the biogas elevated from 0 % to 40 %. The reduction in premixed reactant mixture reactivity not only initiated flame temperature profile deformation but also reduced the peak Damköhler number significantly. The peak Damköhler number was lowered by a factor of ∼ 1.5 when carbon dioxide dilution in the biogas elevated by 40 %. The premixed combustion was directed into the thin reaction flamelets zone with elevated carbon dioxide mass fraction, owing to the intensified flow fluctuation. This, in turn, elevates the normalised flame turbulent propagating speed, gas flow average velocities and turbulent kinetic energy, notwithstanding that heat release rate and averaged laminar flame speed declined. In all, the presence of carbon dioxide has been shown to lower the ammonia/methane mixture reactivity whilst escalating the reacting flow fluctuation.

Simple model for tokamak outer midplane electron temperature profile in scrape-off-layer verified by SOLPS-ITER simulations

A simple analytical model for the estimation of scrape-off-layer (SOL) electron temperature profile in the equatorial outer midplane (OMP) is suggested. It is demonstrated that the OMP electron temperature profile in the SOL can be approximated by a power function of the radial coordinate for constant anomalous perpendicular transport coefficients. The obtained profile gives a slower radial decrease with respect to exponential fitting, which is widely used for OMP electron temperature estimation in the near-SOL region. It is shown that the analytical profiles are in good agreement with those obtained from SOLPS-ITER simulations for the semi-detached regimes of ITER, JET and ASDEX-Upgrade. They are also in reasonable agreement with experimental Thomson scattering profiles for JET and ASDEX-Upgrade. Analysis based on SOLPS-ITER simulation shows that account of more complicated effects such as energy exchange with ions, convective energy transport, etc, can change quantitatively by factors of the order of unity, but not qualitatively, the radial electron OMP temperature profiles.

Rotational and Gas Temperature Measurements for He-C Plasma: Application to Heterogeneous Carbon Nanotubes Synthesis

Plasmas containing carbon cover a wide range of application, either using graphite electrodes or carbon containing plasma gas. The study of the C2 molecule is an interesting way to get information on moderate temperature part of the discharge. In the case of heterogeneous carbon nanotubes (CNTs) synthesis by electric arc, reasonable yield can be achieved with substitution of boron and/or nitrogen atoms by optimizing synthesis parameters. This is based on the knowledge of the plasma and gas temperatures in the synthesis chamber. While electrodes material is vaporized through the arc, nanotubes formed in the growth zone a few centimeters away, when temperature decreases down to 1200 °C–1500 °C. Molecular temperature is particularly relevant since it corresponds to the outer part of the arc, in contact with the growth zone. In this article, Abel inversion is used on side-on integrated spectral profiles for C2(0,0) Swan band, in order to get radial rotational temperature profiles. In addition, gas temperature measurements are performed using thermocouples in the arc chamber. Results show that a strong plasma temperature gradient is associated with favorable synthesis conditions for carbon-bore-nitrogen nanotubes. Gas thermal homogeneity is reached in the chamber after about 30 s, mainly through convection processes.