Evolution Of Temperature Profiles Research Articles

Impurity accumulation and performance of ITER and DEMO plasmas in the presence of transport barriers

In this work, the impurity accumulations and their performance in the presence of both ITB and ETB in ITER and DEMO plasmas are investigated using a BALDUR integrated predictive modelling code. In these simulations, a combination of a neoclassical transport model NCLASS and an anomalous transport model Mixed Bohm/gyro-Bohm is used. The boundary condition is described at the top of the pedestal, which is calculated theoretically based on a combination of magnetic and flow shear stabilization pedestal width scaling and an infinite-n ballooning pressure gradient model. The toroidal flow is calculated based on the NTV (neoclassical toroidal viscosity) toroidal velocity model. The time evolution of plasma temperature and density profiles of ITER and DEMO (Korean K-DEMO and Japanese DEMO models A, B and C) plasmas are simulated in H-mode scenario with and without ITB formation. It is found that Japanese DEMO model C yields highest plasma temperature; while Korean DEMO yields the best plasma performance among those designs considered. Impurity accumulation is found to be highest in Japanese DEMO model B.

Research on heat transfer characteristic of crude oil during the tubular heating process in the floating roof tank

By means of finite volume method, the heat transfer characteristic of crude oil under the tubular heating in the floating roof tank is investigated by numerical simulation. The evolution of temperature profile and its relationship with the flow pattern is presented in detail. A noticeable finding is that there exists the transformation of the flow pattern which affects the temperature profile apparently during the heating process. Special concern is taken on the evolution of temperature distribution on the interface between oil and the inner wall of the tank. The temperature profile on the top wall, sidewall and base wall of the tank is investigated. It is concluded that the plume induced by natural convection takes most responsibility for the formation of temperature field in the tank. The second factor is the boundary condition of the tank.

Controlled atmosphere pyrolysis apparatus II (CAPA II): A new tool for analysis of pyrolysis of charring and intumescent polymers

A new gasification apparatus has been developed to enable a comprehensive analysis of pyrolysis of charring and intumescent materials. This apparatus provides well defined boundary conditions and highly resolved measurements of mass, temperature and sample profile evolution of a disk-shaped 0.07m diameter material sample exposed to radiant heat. All measurements are collected simultaneously, in a single experiment, and recorded as a function of time. The oxygen concentration in the pyrolysis zone is controlled and can be reduced below 1vol% to ensure that the measurements are free of oxidation effects. The radiation from an external conical heater has been carefully characterized to account for changes in the sample surface position, including the surface's angular orientation. Using an empirical expression, the radiation heat flux can be predicted with less than 2% error based on the known surface position and heat flux set point. The NIST Fire Dynamics Simulator (FDS) has been utilized in the direct numerical simulation mode to investigate convective losses from the sample surfaces. The convective heat transfer coefficient computed for the top (radiation exposed) surface has been found to be dependent on the surface position; its space-averaged value has been validated against experimental measurements. The capabilities of the apparatus are demonstrated using poly(vinyl chloride). It is shown that the apparatus provides repeatable data necessary for modeling of transport processes inside pyrolyzing intumescent solids. Non-one-dimensional nature of these processes is discussed.

ITER ECE Diagnostic: Design Progress of IN-DA and the diagnostic role for Physics

The ECE Diagnostic system in ITER will be used for measuring the electron temperature profile evolution, electron temperature fluctuations, the runaway electron spectrum, and the radiated power in the electron cyclotron frequency range (70-1000 GHz), These measurements will be used for advanced real time plasma control (e.g. steering the electron cyclotron heating beams), and physics studies. The scope of the Indian Domestic Agency (IN-DA) is to design and develop the polarizer splitter units; the broadband (70 to 1000 GHz) transmission lines; a high temperature calibration source in the Diagnostics Hall; two Michelson Interferometers (70 to 1000 GHz) and a 122-230 GHz radiometer. The remainder of the ITER ECE diagnostic system is the responsibility of the US domestic agency and the ITER Organization (IO). The design needs to conform to the ITER Organization’s strict requirements for reliability, availability, maintainability and inspect-ability. Progress in the design and development of various subsystems and components considering various engineering challenges and solutions will be discussed in this paper. This paper will also highlight how various ECE measurements can enhance understanding of plasma physics in ITER.

Research on heat transfer characteristic of waxy crude oil during the gelatinization process in the floating roof tank

By means of additional specific heat capacity and momentum source terms methods, the heat transfer characteristic of waxy crude oil during the gelatinization process in the floating roof tank is investigated by numerical simulation. A new kind of division method for the cooling based on the heat transfer mechanism and behavior is proposed. Special concern is taken on the evolution of gelatinization structure and its relationship with the temperature profile. The gelatinous crude oil first generates in the bottom corner of the tank, and there is always the position where the thickest gelatinization layer locates. The integrated gelatinization layer first generates on the top wall, and then it covers the sidewall. The gelatinization interface is not a plane and variates as the cooling proceeds. The temperature profile is constituted by three low temperature regions near walls and a high temperature region in the center of the tank. Moreover, the evolution of temperature profile, positions with the maximal and minimal temperature, as well as the heat transfer coefficient near walls is illustrated in detail. In addition, the effect from environment temperature and oil property on the gelatinization process is also discussed.

A three-dimensional mathematical model to predict air-cooling flow and temperature distribution of wire loops in the Stelmor air-cooling system

Controlling the forced air cooling conditions in the Stelmor conveyor line is important for improving the microstructure and mechanical properties of steel wire rods. A three-dimensional mathematical model incorporating the turbulent flow of the cooling air and heat transfer of the wire rods was developed to predict the cooling process in the Stelmor air-cooling line of wire rolling mills. The distribution of cooling air from the plenum chamber and the forced convective heat transfer coefficient for the wire loops were simulated at the different locations over the conveyor. The temperature profiles and cooling curves of the wire loops in Stelmor conveyor lines were also calculated by considering the convective heat transfer, radiative heat transfer as well as the latent heat during transformation. The calculated temperature results using this model agreed well with the available measured results in the industrial tests. Thus, it was demonstrated that this model can be useful for studying the air-cooling process and predicting the temperature profile and microstructure evolution of the wire rods.

One-dimensional numerical investigation on the formation of Z-pinch dynamic hohlraum using the code MULTI

Z-pinch dynamic hohlraum can effectively convert Z-pinch plasma kinetic energy into radiation field energy, which has a potential to implode a pellet filled with deuterium-tritium fuel to fusion conditions when the drive current is sufficiently large. To understand the formation process of Z-pinch dynamic hohlraum on JULONG-I facility with a typical drive current of 8-10 MA, a new radiation magneto-hydrodynamics code is developed based on the program MULTI-IFE. MULTI-IFE is a one-dimensional, two-temperature, multi-group, open-source radiation hydrodynamic code, which is initially designed for laser and heavy ion driven fusion. The original program is upgraded to simulate Z-pinch related experiments by introducing Lorentz force, Joule heating and the evolution of magnetic field into the code. Numerical results suggest that a shock wave and a thermal wave will be launched when the high speed plasma impacts onto the foam converter. The thermal wave propagates much faster than shock wave, making the foam become hot prior to the arrival of shock wave. For the load parameters and drive current of shot 0180, the calculated propagation speed of thermal wave and shock wave are about 36.1 cm/s and 17.6 cm/s, respectively. The shock wave will be reflected when it arrives at the foam center and the speed of reflected shock wave is about 12.9 cm/s. Calculations also indicate that the plastic foam will expand obviously due to the high temperature radiation environment (~30 eV) around it before the collision between tungsten plasma and foam converter. The evolution of radial radiation temperature profile shows that a pair of bright strips pointing to the foam center can be observed by an on-axis streak camera and the radiation temperature in the foam center achieves its highest value when the shock arrives at the axis. A bright emission ring moving towards the foam center can also be observed by an on-axis X-ray frame camera. The best time to capture the bright strips and bright emission rings is before the thermal wave reaches the foam center. Even though some amount of X-ray radiation in the foam is expected to escape from the hohlraum via radiation transport process, simulation results suggest that the tungsten plasma can serve as a good hohlraum wall. The radiation temperature is about 80 eV when the dynamic hohlraum is created and can rise more than 100 eV before the shock arrives at the foam center. Most of the X-rays emitted by the wire-array plasma surface have energies below 1000 eV. In this paper, the physical model of the code MULTI-IFE and the simulation results of array implosions on Saturn facility are presented as well.

Thomson scattering of plasma turbulence on PSI-2

The turbulent transport in the edge of fusion reactors can be conveniently simulated by linear plasma devices with long duty cycles. At high input power steady state plasma discharges at PSI-2 exhibit intermittent fluctuations similar to the edge of toroidal plasma devices. As their influence on erosion predictions is obscured by time-averaged measurements a time-resolved Thomson scattering setup is installed and tested at PSI-2. Aided by a fast CMOS camera and conditional averaging a time resolution of 3 µs was achieved for temperature and density profile evolution in Argon and Deuterium discharges. A 40 kHz, m = 1 oscillation with 50 µs coherence time and 1 eV electron temperature amplitude was identified in Argon, while in Deuterium intermittent events were associated with a 4 eV rise in edge temperature and a 10% reduction of bulk density.

Real-time tracking of physical changes and optical anisotropy during drying of aqueous chitosan solution: Modeling of drying

The drying behavior of blade casting aqueous chitosan solution was investigated by means of a custom designed real time characterization system that can track the thickness, weight, temperature and in-plane and out-of-plane birefringence. Beyond a critical solvent concentration, initially isotropic cast solution rapidly develops optical anisotropy as detected by out of plane birefringence measurement while it remains isotropic in plane. Increasing drying temperature and air flow speed can both accelerate the drying rate but change the birefringence level in opposite directions. Lower birefringence was obtained at higher drying temperature while, higher birefringence was observed when the air flow speed is increased. This is due to the cumulative effects of the residual stress development in the film and polymer chains relaxation. Using a thermodynamically consistent model developed in the framework of classical irreversible thermodynamics, we quantitatively describe the drying kinetics and evolution of concentration and temperature profiles during the course of drying of the solvent. It was shown that the model can precisely describe the experimental data without using any fitting parameters.

Transport and micro-instability analysis of JET H-mode plasma during pellet fueling

Transport and micro-instability analysis in a JET H-mode plasma discharge 53212 during the pellet fueling operation is carried out using the BALDUR integrated predictive modeling code with a combination of the NCLASS neoclassical transport model and an anomalous core transport model (either Mixed B/gB or MMM95 model). In this work, the evolution of plasma current, plasma density and temperature profiles is carried out and, consequently, the plasma’s behaviors during the pellet operation can be observed. The NGS pellet model with the Grad-B drift effect included is used to describe pellet ablation and its behaviors when a pellet is launched into hot plasma. The simulation shows that after each pellet enters the plasma, there is a strong perturbation on the plasma causing a sudden change of both thermal and particle profiles, as well as the thermal and particle transports. For the simulation using MMM95 transport model, the change of both thermal and particle transports during pellet injection are found to be dominated by the transport due to the resistive ballooning modes due to the increase of collisionality and resistivity near the plasma edge. For the simulation based on mixed B/gB transport model, it is found that the change of transport during the pellet injection is dominated by the Bohm term. Micro-instability analysis of the plasma during the time of pellet operation is also carried out for the simulations based on MMM95 transport model. It is found that the ion temperature gradient mode is destabilized due to an increase of temperature gradient in the pellet effective region, while the trapped electron mode is stabilized due to an increase of collisionality in that region.

Modeling transport phenomena of ice slurry in an ice forming unit

In this article, multiphase convective and solidification transport phenomena of ice slurry is investigated by developing a one-domain macroscopic model to simulate its formation in a rectangular ice forming unit. Convection, sedimentation, interfacial drag, permeability, remelting and viscosity variations are incorporated into this model through the appropriate governing multiphase transport equations. Validation studies with literature data are performed to determine the most suitable drag law by comparing the position of the interface between the coherent and non-coherent zones. After establishing modified Stokes' Law as the best-suited drag model, solidification study of an aqueous ammonium chloride solution is performed. The results for the evolution of ice fraction, species distribution, temperature profile and multiphase velocity field are presented. Solid fraction gradient, due to the generation of ice particles, has a major influence on the density gradient leading to a counter-clockwise flow current resulting in the homogenization of temperature and species in the generated ice slurry.

Simple predictive electron transport models applied to sawtoothing plasmas

In this work, we introduce two simple transport models to evaluate the time evolution of electron temperature and density profiles during sawtooth cycles (i.e. over a sawtooth period time-scale). Since the aim of these simulations is to estimate reliable profiles within a short calculation time, two simplified ad-hoc models have been developed. The goal for these models is to rely on a few easy-to-check free parameters, such as the confinement time scaling factor and the profiles’ averaged scale-lengths. Due to the simplicity and short calculation time of the models, it is expected that these models can also be applied to real-time transport simulations. We show that it works well for Ohmic and EC heated L- and H-mode plasmas. The differences between these models are discussed and we show that their predictive capabilities are similar. Thus only one model is used to reproduce with simulations the results of sawtooth control experiments on the TCV tokamak. For the sawtooth pacing, the calculated time delays between the EC power off and sawtooth crash time agree well with the experimental results. The map of possible locking range is also well reproduced by the simulation.

Influence of wet conditions on snow temperature diurnal variations: An East Antarctic sea–ice case study

A one-dimensional snow–sea–ice model is used to simulate the evolution of temperature profiles in dry and wet snow over a diurnal cycle, at locations where associated observations collected during the Sea Ice Physics and Ecosystem eXperiment (SIPEX-II) are available. The model is used at two sites, corresponding to two of the field campaign׳s sea–ice stations (2 and 6), and under two configurations: dry and wet snow conditions. In the wet snow model setups, liquid water may refreeze internally into the snow. At station 6, this releases latent heat to the snow and results in temperature changes at the base of the snow pack of a magnitude comparing to the model-observation difference (1–2°C). As the temperature gradient across the snow is in turn weakened, the associated conductive heat flux through snow decreases. At station 2, internal refreezing also occurs but colder air temperatures and the competing process of strengthened heat conduction in snow concurrent to snow densification maintain a steady temperature profile. However, both situations share a common feature and show that the conductive heat flux through the snow may significantly be affected (by 10–20% in our simulations) as a result of the liquid water refreezing in snow, either through thermal conductivity enhancement or direct temperature gradient alteration. This ultimately gives motivation for further investigating the impacts of these processes on the sea–ice mass balance in the framework of global scale model simulations.

Numerical modeling of non-Fourier heat transfer and fluid flow during plasma arc welding of AISI 304 stainless steel

ABSTRACTThis paper is an attempt to study the evolution of temperature profiles and weld pool geometry during plasma arc welding (PAW) by solving the transient Navier–Stokes and Energy equations. The analysis for an AISI 304 stainless steel rectangular plate was carried out using a flexible written program in Fortran. Due to the low accuracy of the Fourier heat transfer equation for short times and large dimensions, a non-Fourier form of heat transfer equation was used. Gaussian heat source is considered as the heat source model. The fluid flow in the molten pool is of interest because it can change the temperature distribution in and around the molten zone. The governing equations for fluid flow were solved by the finite-volume method in which the SIMPLE method was utilized for pressure–velocity coupling. The effects of heat conduction, fluid flow, and force actions at the weld pool were considered. Thermo-physical properties such as thermal conductivity, specific heat, and dynamic viscosity vary as a function of temperature. There are two mechanisms involved which actively cause heat transfer to the surroundings: radiation and convection heat transfer. The numerical results are compared to the experimental data. The results corroborate that the weld pool thickness in the cross section of PAW and the time taken by molten metal to reach the end of thick metal are in good agreement with the experimental measurements. Finally, the results obtained from the assumed Fourier heat transfer are compared for the same study.

Simulation Study of Shenmu Coal Pyrolysis by Gas Heat Carrier Based on a Moving Bed

Coats–Redfern integral method combined with thermogravimetry-mass spectrometry technology was applied to study the evolution of the main pyrolysis products for Shenmu bituminous coal. And a heat transfer, reaction, numerical model of coal pyrolysis by gas heat carrier in a moving-bed reactor is developed. The model can predict the internal temperature profile and pyrolysis volatiles evolution of different coal species as well as the temperature distribution of gas heat carrier versus bed height. The results show that when the temperature of the gas heat carrier increases from 700 to 900 °C, the theoretical bed height of pyrolysis drops from 0.26 to 0.14 m, and the maximum of the devolatilization rate increases from 0.954%·s–1 to 1.382%·s–1. The coal species have significant influence on their temperature-rise pyrolysis process in a gas heat carrier moving-bed reactor. Higher initial temperature or velocity of gas heat carrier, smaller particle size, or moving velocity of coal tends to accelerate the devolatilization rate and shorten the pyrolysis time. This work may provide a theoretic foundation for the reactor amplification and different industrial condition prediction of high-volatile coal pyrolysis in a moving-bed reactor.

Thermal Stabilization of NiTiCuV Shape Memory Alloys: Observations During Elastocaloric Training

The paper presents novel findings observed during the training process of superelastic, elastocalorically optimized Ni–Ti-based shape memory alloys (SMA). NiTiCuV alloys exhibit large latent heats and a small mechanical hysteresis, which may potentially lead to the development of efficient solid-state-based cooling processes. The paper starts with a brief introduction to the underlying principles of elastocaloric cooling, illustrating the effect by means of a typical thermodynamic cycle. It proceeds with the description of a custom-built testing platform that allows observation of temperature profiles and heat transfer between SMA and heat source/sink during high-loading-rate tensile tests. Similar to other SMA applications, a training process is necessary in order to guarantee stable performance. This well-known mechanical stabilization affects the stress–strain hysteresis and the cycle-dependent evolution of differential scanning calorimetry results. In addition, it can be shown here that the training is also accompanied by a cycle-dependent evolution of temperature profiles on the surface of an SMA ribbon. The applied training leads to local temperature peaks with intensity, number, and distribution of the temperature fronts showing a cycle dependency. The homogeneity of the elastocaloric effect has a significant influence on the efficiency of elastocaloric cooling process and is a key aspect of the specific material characterization.

Drying kinetics of technical specified rubber

This paper reports the study of crumb rubber drying in different experimental designs. It is important to understand the characteristics of crumb rubber drying in order to formulate a better drying strategy that could give higher energy efficiency. Four experiments were carried out with constant heat at maximum 100°C and a stainless steel container was used to hold the sample of crumb rubber under study. The surface temperature profile of the rubber was investigated using two types of drying methods, normal hot air drying and vacuum drying. It was found that when the sample was dried, external surface temperature for drying with hot air dryer was higher than vacuum dryer. The results showed the evolution of temperature profile was not in good agreement with the prediction which revealed that there was no temperature gradient within the drying samples. The energy consumption for vacuum drying was higher compared to hot air drying, where there was a difference of 0.7079MJ/kg H2O evaporated for drying temperature at 100°C. The best fit model generated from the experimental data was the modified Henderson and Pabis model and the highest effective diffusivity obtained was 5.243×10−9m2/s heating by vacuum oven at 90°C under zero atmospheric pressure.

Profiles of temperature, concentration and supersaturation within atomized droplets during flash-crystallization

Flash-crystallization is a suspension crystallization process to produce small, fine crystals (L50,3= 20–90μm) of substances which are well soluble. A hot and undersaturated solution is atomized into a low vacuum. The small droplets generated partially evaporate and cool down until thermal and mechanical equilibrium is reached. Consequently, they are highly supersaturated in a controlled manner and, thus, enable high nucleation rates. Experiments show that only certain solute–solvent combinations exhibit the high nucleation rates required and, thus, are suitable for flash-crystallization. We show that this observation is not caused solely by the buildup rate of supersaturation, but also by nucleation and growth kinetics. This is concluded by a comparison between the time of flight τf of the droplets in the crystallizer and the buildup time τb needed for the evolution of temperature and concentration profiles inside each droplet. The buildup time of supersaturation τb is negligibly short compared to the time of flight of the droplet. Thus, the driving force for nucleation and growth rate is present during virtually the entire time of flight, and therefore, slow nucleation and growth kinetics are the reason for the behavior observed. The model proposed is in good agreement with data measured.

Theoretical and Experimental Investigations of Wave-Induced Vertical Mixing

Theoretical investigations supported by a series of original laboratory experiments are conducted to study a wave-induced vertical mixing process. The derived semi-analytical solution is very efficient and is applied to predict the effects of water waves on the temperature changes and the evolution of temperature profiles. The results indicate that waves increase a mixing process. The rate of change of the temperature is higher when waves contributed to mixing process and this process increases with increasing the wavelength to water depth ratio. The analysis indicates that for typical ocean waves the contribution of water waves to mixing may be several orders of magnitude higher than a corresponding contribution arising from the classical diffusion process. This implies a need to conduct more theoretical studies and experimental investigation on the effect of water waves on mixing processes. A series of original laboratory experiments were conducted in the insulated wave flume to verify the derived model. The comparisons show a reasonable agreement between predicted and measured temperature profiles. A reasonable agreement between theoretical results and experimental data is observed for the whole considered range of initial temperature distributions. The comparisons indicate that the model is applicable even to cases when gradients in temperature distributions over water depth are fairly high.

Temporal evolution of electron density and electron temperature profiles in a non-thermal atmospheric-pressure plasma measured by laser Thomson scattering

The laser Thomson scattering technique has been applied for measuring the spatiotemporal changes in the electron density (ne) and electron temperature (Te) of a capacity-coupled micro-discharge generated in neon gas at near-atmospheric pressure. A significant difference has been observed in temporal behavior between ne and Te after the discharge generation. The value of ne decreases monotonically from t = 25 ns when the electrical input is truncated. On the other hand, Te is approximately 1.7 eV at 15 ns and, after this point, Te rapidly decreases to about 0.8 eV. Subsequently, Te decreases gradually. These features are discussed on the basis of the recombination processes.