Radial Temperature Profiles Research Articles

Deprojection of X-ray data in galaxy clusters: confronting simulations with observations

ABSTRACT Numerical simulations with varying realism indicate an emergent principle−multiphase condensation and large cavity power occur when the ratio of the cooling time to the free-fall time (tcool/tff) falls below a threshold value close to 10. Observations indeed show cool-core signatures when this ratio falls below 20–30, but the prevalence of cores with tcool/tff ratio below 10 is rare as compared to simulations. In X-ray observations, we obtain projected spectra from which we have to infer radial gas density and temperature profiles. Using idealized models of X-ray cavities and multiphase gas in the core and 3D hydro jet-ICM simulations, we quantify the biases introduced by deprojection based on the assumption of spherical symmetry in determining tcool/tff. We show that while the used methods are able to recover the tcool/tff ratio for relaxed clusters, they have an uncertainty of a factor of 2−3 in systems containing large cavities (≳ 20 kpc). We also show that the mass estimates from these methods, in the absence of X-ray spectra close to the virial radius, suffer from a degeneracy between the virial mass (M200) and the concentration parameter (c) in the form of M200c2 ≈ constant. Additionally, the lack of soft-X-ray (≲ 0.5 keV) coverage and poor spatial resolution makes us overestimate min(tcool/tff) by a factor of few in clusters with min(tcool/tff) ≲ 5. This bias can largely explain the lack of cool-core clusters with min(tcool/tff) ≲ 5.

Transmission electron microscopy study of a high burnup U-10Zr metallic fuel

To support the development of U-10 wt.% Zr (U-10Zr) metallic fuel for Generation IV sodium-cooled fast reactors, we analyzed a Na-bonded solid U-10Zr fuel cross-section that was irradiated to a burnup of approximately 13.2 at.% at the Fast Flux Test Facility (FFTF). Advanced characterization techniques, including site-specific sample preparation by focused ion beam (FIB) and scanning transmission electron microscopy (STEM), were used to reveal the Zr redistribution and characterize the fuel matrix and secondary phases (such as solid fission products) present at the end of life. Results showed that the fuel pin cross-section is divided into three major concentric zones: a Zr-rich central region, a Zr-lean intermediate region, and a Zr intermediate peripherical region. The phase characterization revealed that the irradiation environment enhanced the development and stabilization of phases not predicted by the standard equilibrium U-Zr phase diagrams. Comparing the current results with the ones from previous studies, it is reaffirmed that the radial temperature profile and the time spent in the reactor, rather than the fuel burnup, are the two factors that most influence the formation of redistribution zones and their extension along the fuel cross-section. Various solid fission products, such as lanthanides, ZrRu, BaTe, CsI, and Ba and Sr oxides, precipitated inside the fission gas pores. This study provides unprecedented nanoscale understandings in the irradiated U-10Zr fuel system that may benefit fuel performance modelling and advanced fuel development.

Investigation of influence of wall temperature on particulate deposition using novel dynamic microscopic setup

This study investigates the influence of the wall temperature on the wax particulate deposition mechanism, analyzing the average deposit thickness, the growth rate, and agglomerates of wax crystals using a state-of-the-art microscopic dynamic in-situ visualization technique. The higher the wall temperature, the lower the growth rate and the thinner the deposit thicknesses formed, showing good agreement with conventional flow-loop observations. Similarly, the higher the wall temperature, the smaller the agglomerates formed in laminar cases. Furthermore, the wall temperature has a more significant influence in the laminar case than turbulent. A reduction of 69.3% on the final average deposit thickness measurements was obtained under the laminar flow regime for an increase of 1.9 °C in the wall temperature, while for turbulent flow regimes, the maximum reduction in average deposit thickness was observed to be no higher than 44.4%, even though the wall temperature was varied 3.2 °C. CFD simulations were conducted to determine the radial temperature profile of the oil, showing that the higher the flow rate becomes, the less variation is observed in the radial temperature. The simulated temperature boundary layer thickness for laminar cases was approximately equal to 4.16 mm, while for the turbulent case it is approximately 2.86 mm.

A 3D space-marching analytical model for geothermal borehole systems with multiple heat exchangers

We present a novel, three-dimensional (3D), space-marching analytical framework that accurately predicts and evaluates the thermal performance of a geothermal borehole system with single or multiple N-by-N heat exchangers. The procedure for this model which is associated with the key novelties of this work is threefold. First, a radial temperature profile in a single borehole arrangement is solved through an exact solution using the Green’s function. A time-dependent convective boundary is prescribed around the borehole wall. Second, an axial temperature distribution in this single borehole is calculated by a space-marching algorithm, which updates the convective boundary at every depth by obtaining the heat transfer fluid (HTF) temperature via an energy balance. Third, the single borehole in 2D is extended to a N-by-N arrangement in 3D by the thermal superposition with algebraic equation based on each borehole’s location. The developed 3D model is verified with numerical results using the finite element method and validated against a field-scaled experimental data in the literature in regards to the HTF temperature. Further, the influences of borehole distance, ground thermal conductivity and mass flow rate of the HTF are studied. It can be concluded that this 3D space-marching analytical framework is capable of predicting transient temperature profile of any N-by-N geothermal boreholes subjected to a time-dependent boundary in an accurate and computationally efficient manner, which in turn facilitates the thermal design and implementation of geothermal systems for energy extraction.

Investigation of the stability, radiation, and structure of laminar coflow diffusion flames of CH4/NH3 mixtures

The stability, radiation, and structure of laminar axisymmetric CH4/NH3/air diffusion flames have been studied using photographic images, spectrally resolved measurements of flame radiation, and the spatial distribution of temperature and major species mole fractions obtained by spontaneous Raman scattering. The fit procedure for the Raman spectra of NH3 includes a hitherto unquantified overtone feature, whose inclusion in the fit significantly improves the NH3 fraction obtained. Nitrogen is used to replace NH3 to separate chemical effects of NH3 addition from those due to dilution. The results show that NH3 addition drastically reduces radiation from carbon-containing species, with progressively increasing strong chemiluminescence from excited NO2 and NH2, indicating a substantial change in flame chemistry. While the Rayleigh/Mie scattering from soot particles is still observed in the Raman spectra at 28% NH3 addition, 46% NH3 in the fuel is seen to suppresses soot formation effectively. The measured axial and radial profiles of temperature and major species indicate a substantial contribution from radial transport from the reaction zone, seriously complicating the relation between composition, mixture fraction, and the corresponding equilibrium temperature and mole fractions.

Research on size segregation dynamics and processes of a binary mixture dense granular flow

This study employed an experimental approach to investigate the effects of various filling degrees of the granular bed and the rotation speed on size-induced particle segregation behavior in an almost fully filled double-walled rotating drum. The distributions of the concentrations of bicolor particles in the system were obtained via image processing to determine the segregation state. The dynamics of the mixture flow including the statistical distribution, the azimuthal angle and radial direction granular temperature profiles were measured and calculated via particle-tracking velocimetry (PTV). The results were similar for the Brazil-nut effect and its reverse in the radial direction at high or low rotation speeds. When the rotation speed or filling degree was changed, the effect on two different particle sizes in the binary mixture system was inconsistent, and different flow mechanisms led to different segregation patterns. Two phase diagrams with the rotation speed and filling degree and the magnitude and position of the maximum granular temperature as the space enabled the prediction of segregation states.

Modeling of argon–steam thermal plasma flow for abatement of fluorinated compounds

This study presents a numerical model of the hybrid-stabilized argon–steam thermal DC plasma torch of a new design for generating an argon–steam plasma suitable for efficient abatement of persistent perfluorinated compounds. The model includes the discharge region and the plasma jet flowing to the surrounding steam atmosphere contained in a plasma-chemical chamber. Compared to previous studies, the torch had a smaller nozzle diameter (5.3 mm) and a reduced input power (20–40 kW) and arc current (120–220 A). The outlet region for the plasma jet extends to 20 cm downstream of the exit nozzle. Fluid dynamic and thermal characteristics together with diffusion of argon, hydrogen and oxygen species, and distribution of plasma species in the discharge and the plasma jet are obtained for currents from 120 to 220 A. The results of the calculations show that the plasma jet exhibits high spatiotemporal fluctuations in the shear layer between the plasma jet and colder steam atmosphere. The most abundant species in the plasma jet are hydrogen and oxygen atoms near the jet center, and molecules of H2, O2 and OH in colder surrounding regions. Satisfactory agreement is obtained with measurements of the radial temperature and electron number density profiles near the jet center close to the nozzle exit.

Experimental Radial Profiles of Early Time (<4 μs) Neutral and Ion Spectroscopic Signatures in Lightning‐Like Discharges

AbstractThis study presents experimental results for the radial and temporal variation of neutral and ion spectroscopic signatures emerging from the heated channel of lightning‐like discharges diagnosed with a high speed (900,000 fps) imaging spectrograph. Light emissions emanate from three regions: an inner core (up to ∼2 mm), an external sheath (up to ∼4 mm) featuring a sudden temperature increase, and further optical emissions forming a dim glow from 4 mm up to 16 mm. The optical emissions are initially (<1.11 μs) dominated by the N2 first positive system at 660.8 nm and by the N II ion line at 661.05 nm. Between 1.11 and 3.33 μs the optical emissions are dominated by Hα (656.3 nm) and O II ion (656.54 nm) lines. The N II ion line at 648.20 nm prevails in the outer dim glow region (9–12 mm) before 2.22 μs. Spectroscopic signals were used to experimentally derive the time dynamics of the electron density and electron/gas temperature radial profiles, which allowed the estimation of the early time overpressure pulse, electrical conductivity and concentrations of key molecular species (N2, NO, O2, OH, H2, N2O, NO2, HO2, O3, and H2O) along the radial axis of the heated air plasma channel. These populations were calculated from the overpressure pulse, assuming that they were produced from humid (50%) air under thermal equilibrium conditions. OH is found to be the second most abundant molecular species (after NO) directly generated by heated lightning‐like channels.

Modeling a continuous digester extraction screen zone with an approximated flow model

Abstract Phenomenological continuous digester models are normally limited to axial flow. However, under industrial conditions, liquor also flows radially in extraction zones. While multidimensional expansion using computation fluid dynamics is possible, the increase in mathematically complexity and computation burden is intractable for online control and optimization. In this work, an approximate algebraic flow model is proposed which removes the need to evaluate momentum continuity. The model, based on streamlines, superimposes radial and axial flow profiles. The dynamic response, when compared against a single continuous stirred tank model, was found to better predict the process response during industrial trials. Simulation studies suggest enhanced lignin removal and variability reductions are possible by increasing recirculated liquor flow rates in the zone, a result of flattening the radial chemical and temperature profiles in the chip phase. However, a minimum occurs as chemical and energy losses in the extracted flow leaving the zone take precedence.

Analysis of the Effect of Central Gap Size on the Temperature Profile and Fissile Content in the Annular Nuclear Fuel Rod

The perturbation in temperature profile and fissile content due to variation in the central gap of an isolated annular cylindrical fuel rod of a pressurized water reactor was studied by analytical calculation. Four different models namely UO2+Zircaloy-4+He, UO2+ Zr-1%Nb +He, MOX+Zircaloy-4+He, and MOX+ Zr-1%Nb +He were considered. The radial temperature profile was generated for different ratios (α) of outer to inner fuel radius. Lower fuel temperature was observed for small values of α and vice versa. The peak fuel temperature and temperature drop across the fuel pellets were calculated. Models of MOX fuel showed higher peak fuel temperature and large temperature drop than the models of UO2 for the same fuel cladding. Zr-1%Nb cladding results in a slightly higher fuel temperature than Zircaloy-4 for the same fuel composition. The faster changes of these parameters with α were found for UO2 than MOX fuel. The change in fissile loading with α was also studied and a sharp increase is observed if exceeds α=2.50. DUJASE Vol. 6 (2) 72-76, 2021 (July)

Thermal radiation effects on heat transfer in slender packed-bed reactors: Particle-resolved CFD simulations and 2D modeling

Radial heat management is crucial for a safe and stable operation of fixed-bed reactors with small tube-to-particle diameter ratios (N). Under high temperature conditions, thermal radiation can contribute substantially to the overall heat transfer. In the present work, the influence of radiation is studied with particle resolved computational fluid dynamics (PRCFD) in a fixed-bed reactor consisting of 1000 spheres and rings with N = 5.1 over 300 < Rep< 2000 and for three different temperature levels (300–800 ∘C). Two heat transfer parameters, i.e., the wall Nusselt number Nuw and the effective radial thermal conductivity of the bed keff, r, are derived directly from PRCFD. While the radiation effect is minor in keff, r, it is substantial for Nuw, which is not captured adequately in the current correlations presented in literature. Depending on the temperature level and flow conditions, thermal radiation between the hot wall and the packed bed intensifies the radial heat transfer represented by an increase of up to 170 % in Nuw and 65% in keff, r. A 2D axisymmetric pseudo-homogeneous model including the derived heat transfer parameters can predict the radial temperature profile of the PRCFD with reasonable accuracy also with radiation except for the near-wall region.

Thermal hydraulic characteristics of silicon irradiation in a typical MTR reactor

Abstract In this work, a three-dimensional study is conducted for silicon ingot irradiation facility in a typical MTR reactor. The silicon ingot heat generation is allowed to change around its nominal value in the range of 0.25, 0.5, 0.75, 1.0, and 1.25 W/g. The dimensionless clearance ratio ζ between the ingot and the outer casing is changed for values of 0.01, 0.05, 0.1, 0.15, and 0.2. The computational fluid dynamics code ANSYS FLUENT is employed to carry out these calculations. The temperature profile inside the silicon ingot during irradiation is of significant importance for uniform doping. Therefore, the impact of Rayleigh number and dimensionless clearance ratio ζ on the radial and axial temperature profiles through the ingot is reported. A best estimate correlation for the silicon irradiation facility global Nusselt number in terms of Rayleigh and dimensionless clearance ratio is presented. The dimensionless clearance ratio ζ value of 0.05 gives the best thermal hydraulic performance. Comparison with the available experimental correlations in the literature shows good agreement.

High-βp scenario realized by the integration of internal and external transport barriers in the HL-2A tokamak

High-βp scenario addresses needs for an attractive tokamak fusion reactor design, where βp is the normalized plasma poloidal beta. High-βp experiments have been performed during recent years in the HL-2A tokamak. The high-performance region is realized by the integration of internal and external transport barriers which are dubbed as ITBs and ETBs, namely, double transport barriers (DTBs), with the high-power NBI heating. Generally, the ITB forms and becomes strong after the NBI injection on HL-2A. Subsequently, the edge ion temperature and toroidal rotation increase, as a result that the ETB or pedestal creates and L-H transition occurs. A high-βp (βp∼3) scenario is obtained with Ip∼110 kA and q95∼5, and another high-βp (βp∼2.7) scenario is also realized with Ip∼160 kA and q95∼4.2. The two high-βp scenarios are both characterized by a large-radius ITB and an ETB. However, the two scenarios are different. For the former there are strong large-radius ITB and weak ETB on radial ion temperature profiles, but for the later there are weak large-radius ITB and strong ETB. Although two high-βp scenarios on HL-2A have been accessed, however they are both transient. In addition, MHD instabilities in high-βp scenarios are also present for a high fusion gain and reactor relevant high fusion-density plasma.

Using AGN light curves to map accretion disc temperature fluctuations

ABSTRACT We introduce a new model for understanding AGN continuum variability. We start from a Shakura–Sunyaev thin accretion disc with a steady-state radial temperature profile T(R) and assume that the variable flux is due to axisymmetric temperature perturbations δT(R, t). After linearizing the equations, we fit UV–optical AGN light curves to determine δT(R, t) for a sample of seven AGNs. We see a diversity of |δT/T| ∼ 0.1 fluctuation patterns which are not dominated by outgoing waves travelling at the speed of light as expected for the ‘lamppost’ model used to interpret disc reverberation mapping studies. Rather, the most common pattern resembles slow (v ≪ c) ingoing waves. An explanation for our findings is that these ingoing waves trigger central temperature fluctuations that act as a lamppost, producing lower amplitude temperature fluctuations moving outwards at the speed of light. The light curves are dominated by the lamppost signal – even though the temperature fluctuations are dominated by other structures with similar variability time-scales – because the discs exponentially smooth the contributions from the slower moving (v ≪ c) fluctuations to the observed light curves. This leads to light curves that closely resemble the expectations for a lamppost model but with the slow variability time-scales of the ingoing waves. This also implies that longer time-scale variability signals will increasingly diverge from lamppost models because the smoothing of slower moving waves steadily decreases as their period or spatial wavelength increases.

Numerical investigations of flow and heat transfer of polymer melt in underwater extrusion pelletizers

The thermoplastics compounding industry extensively utilizes underwater die-face pelletizers, where, the polymer melt is extruded through a capillary, then cut, stress-relaxed and cooled by a medium, which all have a significant impact on the final pellet quality. Some of the common practical problems in these applications are referred to as (1) “die-hole freeze-off”, due to the low temperatures and (2) “pellet marriages”, due to the polymer being too soft. In order to address some of these issues, three-dimensional (3D) computational fluid dynamics (CFD) calculations of non-Newtonian flow of a polymer in an extruder, along with the turbulent flow of heating oil and the conjugate heat transfer through the die are carried out using ANSYS Fluent. The computational model is validated by comparing predictions of a probed temperature in the die plate, and pressure drop within the polymer, to experimental measurements in the industrial-scale pelletizer, for five different operating conditions, with the maximum resulting error being <13%. In addition, this study investigates the effect of three control parameters: (Case Study I) thermal conductivity of the die plate surfacing, (Case Study II) inlet temperature of the polymer and (Case Study III) inlet mass flow rate of the polymer, on potential pellet quality, by analyzing the flow and thermal characteristics. Specifically, contours of temperature in the die plate and polymer, and also axial and radial profiles of pressure, viscosity, temperature, velocity magnitude, shear rate and shear stress, in the polymer, are analyzed in detail to assess the possibilities of freeze-off and higher yield loss. The temperature behavior showed that die plate surfacing with lower thermal conductivity would delay freeze-off. Shear-stress profiles helped identify the cases with higher probable freeze-off, which included those with polymer inlet temperatures >225∘C and mass flow rates <8 kg/hr and >12 kg/hr.

Continuum reverberation mapping of the quasar PG 2130+099

Aims. We present the results of an intensive six-month optical continuum reverberation mapping campaign of the Seyfert 1 galaxy PG 2130+099 at redshift z = 0.063. The ground-based photometric monitoring was conducted on a daily basis with the robotic 46 cm telescope of the WISE observatory located in Israel. Specially designed narrowband filters were used to observe the central engine of the active galactic nucleus (AGN), avoiding line contamination from the broad-line region (BLR). We aim to measure inter-band continuum time lags across the optical range and determine the size-wavelength relation for this system. Methods. We used two methods, the traditional point-spread function photometry and the recently developed proper image subtraction technique, to independently perform the extraction of the continuum light curves. The inter-band time lags are measured with several methods, including the interpolated cross-correlation function, the z-transformed discrete correlation function, a von Neumann estimator, JAVELIN (in spectroscopic mode), and MICA. Results. PG 2130+099 displays correlated variability across the optical range, and we successfully detect significant time lags of up to ∼3 days between the multiband light curves. We find that the wavelength-dependent lags, τ(λ), generally follow the relation τ(λ)∝λ4/3, as expected for the temperature radial profile T ∝ R−3/4 of an optically thick, geometrically thin accretion disk. Despite that, the derived time lags can also be fitted by τ(λ)∝λ2, implying the possibility of a slim, rather than thin, accretion disk. Using the flux variation gradient method, we determined the AGN’s host-galaxy-subtracted rest frame 5100 Å luminosity at the time of our monitoring campaign with an uncertainty of ∼18% (λL5100 = (2.40 ± 0.42)×1044 erg s−1). While a continuum reprocessing model can fit the data reasonably well, our derived disk sizes are a factor of ∼2 − 6 larger than the theoretical disk sizes predicted from the AGN luminosity estimate of PG 2130+099. This result is in agreement with previous studies of AGN/quasars and suggests that the standard Shakura-Sunyaev disk theory has limitations in describing AGN accretion disks.

Probing Hot Gas Components of the Circumgalactic Medium in Cosmological Simulations with the Thermal Sunyaev–Zel’dovich Effect

Abstract The thermal Sunyaev–Zel’dovich (tSZ) effect is a powerful tool with the potential for constraining directly the properties of the hot gas that dominates dark matter halos because it measures pressure and thus thermal energy density. Studying this hot component of the circumgalactic medium (CGM) is important because it is strongly impacted by star formation and active galactic nucleus (AGN) activity in galaxies, participating in the feedback loop that regulates star and black hole mass growth in galaxies. We study the tSZ effect across a wide halo-mass range using three cosmological hydrodynamical simulations: Illustris-TNG, EAGLE, and FIRE-2. Specifically, we present the scaling relation between the tSZ signal and halo mass and the (mass-weighted) radial profiles of gas density, temperature, and pressure for all three simulations. The analysis includes comparisons to Planck tSZ observations and to the thermal pressure profile inferred from the Atacama Cosmology Telescope (ACT) measurements. We compare these tSZ data to simulations to interpret the measurements in terms of feedback and accretion processes in the CGM. We also identify as-yet unobserved potential signatures of these processes that may be visible in future measurements, which will have the capability of measuring tSZ signals to even lower masses. We also perform internal comparisons between runs with different physical assumptions. We conclude (1) there is strong evidence for the impact of feedback at R 500, but that this impact decreases by 5R 500, and (2) the thermodynamic profiles of the CGM are highly dependent on the implemented model, such as cosmic-ray or AGN feedback prescriptions.

A Hydro-particle-mesh Code for Efficient and Rapid Simulations of the Intracluster Medium

Abstract We introduce the cosmological HYPER code based on an innovative hydro-particle-mesh (HPM) algorithm for efficient and rapid simulations of gas and dark matter. For the HPM algorithm, we update the approach of Gnedin &amp; Hui to expand the scope of its application from the lower-density intergalactic medium (IGM) to the higher-density intracluster medium (ICM). While the original algorithm tracks only one effective particle species, the updated version separately tracks the gas and dark matter particles, as they do not exactly trace each other on small scales. For the approximate hydrodynamics solver, the pressure term in the gas equations of motion is calculated using robust physical models. In particular, we use a dark matter halo model, ICM pressure profile, and IGM temperature–density relation, all of which can be systematically varied for parameter-space studies. We show that the HYPER simulation results are in good agreement with the halo model expectations for the density, temperature, and pressure radial profiles. Simulated galaxy cluster scaling relations for Sunyaev–Zel’dovich (SZ) and X-ray observables are also in good agreement with mean predictions, with scatter comparable to that found in hydrodynamic simulations. HYPER also produces lightcone catalogs of dark matter halos and full-sky tomographic maps of the lensing convergence, SZ effect, and X-ray emission. These simulation products are useful for testing data analysis pipelines, generating training data for machine learning, understanding selection and systematic effects, and for interpreting astrophysical and cosmological constraints.

ASTI: Data assimilation system for particle and heat transport in toroidal plasmas

ASTI, a data assimilation system for integrated transport simulation of fusion plasma, has been developed to predict and control the fusion plasma behavior. ASTI employs the ensemble Kalman filter (EnKF) and smoother (EnKS) as data assimilation methods and the integrated transport simulation code for helical fusion plasma, TASK3D, as the system model. ASTI assimilates the time-series data of measured temperature and density radial profiles into the particle and heat transport simulation. In this study, we consider the uncertainties included in the density, temperature, transport model, neutral beam injection (NBI) heating model, and particle source model. We apply ASTI to 12 experimental data sets of the NBI-heated plasma in Large Helical Device (LHD) and investigate the validity of estimation and the prediction performance of ASTI. The obtained radial profile and time evolution of density, electron temperature, and ion temperature agree well with the experimental data sets. Faster and more accurate integrated transport simulation is realized byASTI than the previous integrated simulation of fusion plasmas.

Energy consistent Gaussian integral model for jet with off-source heating

Volumetrically heated jets mimic fluid flow in cloudy plumes, and the entrainment rate coefficient in such jets can vary significantly along the axial direction. In this work, we formulate an energy consistent Gaussian integral model for volumetrically heated jets, in which the entrainment rate coefficient is dynamically evolved along the axis. The widths for radial profiles of velocity, tracer concentration, and temperature are allowed to evolve separately. The results from the model agree reasonably well with corresponding integral statistics obtained from Large Eddy Simulations.