Temperature Fluctuation Levels Research Articles

The effect of materials, process settings and screw geometry on energy consumption and melt temperature in single screw extrusion

Polymer extrusion is an energy intensive production process and process energy efficiency has become a key concern in the current industry with the pressure of reducing the global carbon footprint. Here, knowledge of the pattern of energy usage and losses of each component in the plant is highly useful in the process energy optimization. Moreover, it is essential to maintain the melt quality while improving the energy efficiency in polymer processing. In this work, an investigation was made on the total energy consumption, drive motor energy consumption, power factor and the melt temperature profile across the die melt flow (as an indication of the melt thermal quality) of an industrial scale extruder with three different screw geometries, three polymer types and wide range of processing conditions (altogether 135 different processing situations were observed). This aims to widen the knowledge on process energy and thermal behaviors while exploring possible correlation/s between energy demand and melt quality (in terms of melt temperature fluctuations across the melt flow). The results showed that the level and fluctuations of the extruder’s power factor is particularly dependent upon the material being processed. Moreover, it seems that there is a relation between the level of energy demand of the heaters and the level of melt temperature fluctuations. While the extruder specific energy consumption decreases with increasing screw speed, specific energy consumption of the drive motor may have either increasing or decreasing behavior. Overall, this study provides new insights in a wide range on process energy demand and melt thermal quality in polymer extrusion. Moreover, further research is recommended to establish strong correlation/s between process energy consumption and melt thermal quality which should help to enhance process control and hence the product quality in single screw polymer extrusion.

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

Long wavelength turbulent electron temperature fluctuations (kyρs < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (kyρs ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

Spatially resolved measurements of two-dimensional turbulent structures in DIII-D plasmas

Two-dimensional observations of spatially coherent electron temperature fluctuations at drift-wave scales (k ∼ 1 cm−1) have been made using the electron cyclotron emission imaging diagnostic on the DIII-D tokamak. These measurements enable the extraction of spectral properties, including poloidal dispersion relations. Temperature fluctuation levels are found to be Tẽ/⟨Te⟩=1.2%, and the phase velocity of the fluctuations is found to be constant across frequencies, consistent with modes having real frequencies low compared to the rotation-induced Doppler shifts. Comparisons with radially global linear gyrokinetic simulations suggest that the observed modes may be trapped electron modes.

COMPARISON BETWEEN 2D TURBULENCE MODEL ESEL AND EXPERIMENTAL DATA FROM AUG AND COMPASS TOKAMAKS

<!-- p, li { white-space: pre-wrap; } --><p style="text-indent: 0px; margin: 0px;">In this article we have used the 2D fluid turbulence numerical model, ESEL, to simulate turbulent transport in edge tokamak plasma. Basic plasma parameters from the ASDEX Upgrade and COMPASS tokamaks are used as input for the model, and the output is compared with experimental observations obtained by reciprocating probe measurements from the two machines. Agreements were found in radial profiles of mean plasma potential and temperature, and in a level of density fluctuations. Disagreements, however, were found in the level of plasma potential and temperature fluctuations. This implicates a need for an extension of the ESEL model from 2D to 3D to fully resolve the parallel dynamics, and the coupling from the plasma to the sheath.</p>

Dark Energy Stars and the Cosmic Microwave Background

Cosmological models with a large cosmological constant are unstable due to quantum critical fluctuations at the de Sitter horizon. Due to this instability the space-time in these models will quickly evolve into a Friedmann-like expanding universe containing dark energy stars and radiation. In this paper it is pointed out that this provides a simple explanation for both the observed radiation entropy per gram of dark matter and the level of temperature fluctuations in the cosmic microwave background. A novel prediction is that large dark energy stars provide the seeds for the formation of galaxies.

A flux-matched gyrokinetic analysis of DIII-D L-mode turbulence

Previous nonlinear gyrokinetic simulations of specific DIII-D L-mode cases have been found to significantly underpredict the ion heat transport and associated density and temperature fluctuation levels by up to almost one of order of magnitude in the outer-core domain, i.e., roughly in the last third of the minor radius. Since then, this so-called shortfall issue has been subject to various speculations on possible reasons and furthermore motivation for a number of dedicated comparisons for L-mode plasmas in comparable machines. However, only a rather limited number of simulations and gyrokinetic codes has been applied to the original scenario, thus calling for further dedicated investigations in order to broaden the scientific basis. The present work contributes along these lines by employing another well-established gyrokinetic code in a numerically and physically comprehensive manner. Contrary to the previous studies, only a mild underprediction is observed at the outer radial positions which can furthermore be overcome by varying the ion temperature gradient within the error bars associated with the experimental measurement. The significance and reliability of these simulations are demonstrated by benchmarks, numerical convergence tests, and furthermore by extensive validation studies. The latter involve cross-phase and cross-power spectra analyses of various fluctuating quantities and confirm a high degree of realism. The code discrepancies come as a surprise since the involved software packages had been benchmarked repeatedly and very successfully in the past. Further collaborative effort in identifying the underlying difference is hence required.

Response of Soot Temperature to Unsteady Inlet Airflow Under Modulated Condition and Naturally Occurring Combustion Dynamics

The response of soot temperature to unsteady inlet airflow is characterized using pyrometry. The unsteady inlet airflow is achieved by either modulating inlet air or naturally occurring unstable flame, running on a jet fuel at fuel-rich conditions. The inlet air is modulated by a siren device running at frequencies between 150 and 250 Hz and up to 60% of modulation level (u'/um) is achieved. Also, the combustor can be run naturally unstable at the same inlet operating condition by changing the combustor length. For pyrometry, the emission from whole flame at 660 nm, 730 nm, and 800 nm is recorded and the three-color pyrometry is used to measure soot temperature. The effect of nonisothermal distribution of soot in flame on the measured temperature is also considered. The level of overall temperature fluctuation under inlet flow modulation (Trms/Tmean) is about an order of magnitude lower than that of flame emission fluctuation (Irms/Imean). Under naturally occurring instability, the measured soot temperature is in phase with the pressure measured in the combustor, indicating that the measured soot temperature can be used as a quantity related to combustion dynamics for fuel-rich sooty flames.

Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

In this paper, we report observations of reduced core (0.40 < ρ < 0.95) fluctuations in the edge localized mode (ELM)-free high-confinement regime, I-mode, at Alcator C-Mod (Marmar et al2009 Nucl. Fusion 49 104014). Long wavelength (kθρs < 0.5) density fluctuation levels are observed to decrease from L-mode levels by up to 30% in I-mode, while long wavelength (kθρs < 0.3) electron temperature fluctuation levels are observed to decrease by up to 70% in I-mode. This reduction in core turbulence is correlated with the increases in confinement in I-mode compared to L-mode. As the pedestal temperature increases across the L–I transition, core density fluctuations (0.40 < ρ < 0.95) are reduced prior to the onset of the edge-localized (ρ ∼ 0.99–1.0) weakly coherent mode (WCM) and prior to the reduction of low-frequency (ρ ∼ 0.99–1.0) turbulence in the edge/pedestal region. This result helps add to our understanding of the dynamics of confinement transitions such as I-mode and H-mode, where changes in edge turbulence are more typically observed to occur prior to changes in core turbulence.

Microwave imaging reflectometry for density fluctuation measurement on KSTAR

A dual-frequency microwave imaging reflectometry system was commissioned to measure both coherent and turbulent electron density fluctuations in KSTAR plasmas. Imaging of the density fluctuations is achieved with an array of 16 vertically aligned detectors and two X-mode probe beam frequencies (tunable over 78–92 GHz between plasma discharges). The system provides the capability of fluctuation measurements with poloidal wavenumbers (kθ) up to ∼3 cm−1 at the maximum sampling rate of 2 MHz. Following extensive laboratory tests, the system was further tested with known coherent density fluctuations during the precursor oscillation of the m/n = 1/1 internal kink mode. The phase information of the reflected beam was compared with the precursor oscillation of the electron temperature measured by an electron cyclotron emission (ECE) radiometer. Density fluctuation levels (δne/ne) at two radial positions separated by the inversion radius (inside and outside) were comparable to temperature fluctuation levels (δTe/Te) from ECE signals. Subsequently, two correlation analysis methods were applied to turbulent fluctuation measurements in a neutral beam heated L-mode plasma to determine the mean poloidal rotation velocities of density fluctuations at two radial positions. The measured mean poloidal velocities were ∼8.4 km s−1 at r/a ∼ 0.6 and ∼5 km s−1 at r/a ∼ 0.7 in the clockwise direction, which differed by 1–2 km s−1 with the projected poloidal velocities from the toroidal rotation velocity measured by charge exchange recombination spectroscopy.

Gyrokinetic simulations of reverse shear Alfvén eigenmodes in DIII-D plasmas

A gyrokinetic ion/mass-less fluid electron hybrid model as implemented in the GEM code [Y. Chen and S. E. Parker, J. Comput. Phys. 220, 837 (2007)] is used to study the reverse shear Alfvén eigenmodes (RSAE) observed in DIII-D, discharge #142111. This is a well diagnosed case with measurement of the core-localized RSAE mode structures and the mode frequency, which can be used to compare with simulations. Simulations reproduce many features of the observation, including the mode frequency up-sweeping in time and the sweeping range. A new algorithmic feature is added to the GEM code for this study. Instead of the gyrokinetic Poisson equation itself, its time derivative, or the vorticity equation, is solved to obtain the electric potential. This permits a numerical scheme that ensures the E × B convection of the equilibrium density profiles of each species cancel each other in the absence of any finite-Larmor-radius effects. These nonlinear simulations generally result in an electron temperature fluctuation level that is comparable to measurements, and a mode frequency spectrum broader than the experimental spectrum. The spectral width from simulations can be reduced if less steep beam density profiles are used, but then the experimental fluctuation level can be reproduced only if a collision rate above the classical level is assumed.

CMB fluctuations and string compactification scales

We propose a mechanism for the generation of temperature fluctuations of cosmic microwave background. We consider a large number of fields, such as Kaluza–Klein modes and string excitations. Each field contributes to the gravitational potential by a small amount, but an observable level of temperature fluctuations is achieved by summing up the contribution of typically of order 1014 fields. Tensor fluctuations are hardly affected by these fields. Our mechanism is based on purely quantum effects of the fields which are classically at rest, and is different from the one in slow-roll inflation. Using the observed data, we find constraints on the parameters of this model, such as the size of the extra dimensions and the string scale. Our model predicts a particular pattern of non-gaussianity with a small magnitude.

Electron temperature fluctuations associated with the weakly coherent mode in the edge of I-mode plasmas

New measurements of electron temperature fluctuations associated with the weakly coherent mode (WCM) during improved mode, or I-mode plasmas (Whyte et al 2010 Nucl. Fusion. 50 105005) at Alcator C-Mod (Marmar et al 2007 Fusion. Sci. Technol. 51 3261) are presented in this paper. The measurements are made with a 32-channel, high-resolution profile electron cyclotron emission radiometer. The WCM electron temperature fluctuations are localized to a 1 cm region inside the last closed flux surface. The WCM electron temperature fluctuation level is measured in several different I-mode discharges and is in the range , which is an order of magnitude smaller than the WCM density fluctuation level. The WCM edge fluctuations observed in I-mode are believed to play a role in increasing particle transport but not energy transport in the edge of I-mode plasmas. The large difference between normalized density and electron temperature fluctuation amplitudes provides new evidence that the WCM fluctuations can separately affect energy and particle transport.

Fluctuation Measurement in the Edge Plasma on TST-2

A new technique is used to estimate the amplitude of temperature fluctuation in the edge plasma on TST-2. Langmuir probe current-voltage characteristic curves are conditionally reconstituted in terms of the intensity of the floating potential. High/low electron temperatures are obtained in low/high floating potential phases. As a result, normalized temperature fluctuation levels are found to be about 19 % or larger.

Observation of reduced core electron temperature fluctuations and intermediate wavenumber density fluctuations in H-mode plasmas

In this paper, we report observations of reduced core electron temperature and intermediate-scale density fluctuations in H-mode. Electron temperature fluctuation levels are observed to decrease from L-mode levels ( for kθρs < 0.5 as measured by correlation electron cyclotron emission radiometry) by at least a factor of four in H- and quiescent H-mode regimes in the DIII-D tokamak (r/a = 0.7). Linear stability calculations (using the trapped gyro-Landau fluid (TGLF) code) indicate that the observed temperature fluctuations are associated with L-mode ITG turbulence which is shear-stabilized at the L- to H-mode transition. Recent results from DIII-D provide the first experimental evidence that, in addition, intermediate-scale turbulence (0.5 < kθρs ⩽ 3) is reduced at the L–H transition. A 30–40% prompt reduction (r/a ⩾ 0.7) has been found at the L–H transition in co-injected medium density plasmas, with a larger decrease (⩾75%) observed near the pedestal top. Experimental results and TGLF calculations indicate that intermediate/small scale turbulence persists in H-mode at a reduced amplitude (0.6 ⩽ r/a ⩽ 1) and may substantially contribute to the residual anomalous H-mode electron heat transport.

Uncertainty-Aware Dynamic Power Management in Partially Observable Domains

This paper tackles the problem of dynamic power management (DPM) in nanoscale CMOS design technologies that are typically affected by increasing levels of process and temperature variations and fluctuations due to the randomness in the behavior of silicon structure. This uncertainty undermines the accuracy and effectiveness of traditional DPM approaches. This paper presents a stochastic framework to improve the accuracy of decision making during dynamic power management, while considering manufacturing process and/or environment induced uncertainties. More precisely, variability and uncertainty at the system level are captured by a partially observable semi-Markov decision process with interval-based definition of states while the policy optimization problem is formulated as a mathematical program based on this model. Experimental results with a RISC processor in 65-nm technology demonstrate the effectiveness of the technique and show that the proposed uncertainty-aware power management technique ensures system-wide energy savings under statistical circuit parameter variations.

Analysis of turbulence diffusion and H-mode transition in conjunction with gyrocentre shift at the boundary of fusion devices

A new concept of turbulence transport and diffusion coefficient are derived from the microscopic ( is the localized electric field and B is the magnetic field) drifts at the boundary of fusion devices by characterization of the gyrocentre shift induced by the collisions among electrons, ions and neutrals. It is found that when the viscosity force of the ion–neutral collision is counted, Reynolds numbers of the poloidal ion flow in the vicinity of the tokamak separatrix vary over the critical value between turbulent and laminar flows depending on the plasma parameters such as temperature, neutral density and density fluctuation level, which explains the mechanism of the fast transition from the low confinement mode to the high confinement mode (L/H transition) for the examplar cases.

Effect of temperature fluctuations on high frequency acoustic coupling

This article considers the influence of fluctuations in temperature on acoustic resonance characteristics of a combustion chamber. This analysis is concerned with acoustic coupling experienced in high frequency instabilities. Experiments carried out on a multiple injector combustor (MIC) operating with liquid oxygen and gaseous methane are used to simulate on a model scale the situation prevailing in a liquid rocket thrust chamber. External acoustic modulations are generated by periodically blocking an auxiliary nozzle with a rotating toothed wheel. By continuously changing the rotation velocity, it is possible to apply a linear frequency sweep and obtain the response of the system to an external excitation. It is found that the chamber quality factor under hot fire conditions is reduced with respect to the one measured under cold flow conditions. This is shown to be correlated with the level and spatial extension of temperature fluctuations inside the chamber. Temperature fluctuations induce variations in the speed of sound which in turn perturb the eigenfrequencies of the system and modify its response. This effect is modeled in a simplified way by considering a second order dynamical system featuring an eigenfrequency which fluctuates around its mean value. The dynamics is analyzed by making use of simulations and by the method of averaging. It is shown that when the eigenfrequency fluctuates, the system behaves as if it had an augmented level of dissipation and that this induces a reduction in the quality factor. It is concluded that this mechanism could have an important impact on the development of oscillations in liquid rocket engines.

Thermal effects on Farley–Buneman waves at nonzero aspect and flow angles. I. Dispersion relation

With the increasingly accepted notion that E-region electrostatic plasma waves move at their instability threshold speed when they attain their maximum amplitude, it has become more important to determine just what that threshold speed is supposed to be. An accurate determination requires a calculation of the electron temperature fluctuation level, which can sometimes dramatically influence the results. In this paper, the Grad 8-moment transport equations have been employed with the addition of a generalized electron cooling rate to account for cooling via inelastic collisions, and a general electron volume heating rate that includes frictional heating as a special case. The derived generalized dispersion relation is presented in such a way that a variety of other earlier treatments, including the isothermal and adiabatic limits and an instability associated with electron friction, all fall out transparently, allowing us to easily compare our results with earlier ones while tracking down the physical processes involved. The presentation format is also geared to facilitate the computation of the dispersion relation for the purpose of comparing the theoretical results with observations.

ICONE15-10805 THERMAL FATIGUE IN THE MIXING TEES IMPACTED BY TURBULENT FLOWS AT LARGE GAP OF TEMPERATURE : THE FATHER EXPERIMENT AND THE NUMERICAL SIMULATION

Thermal fatigue is one significant long term degradation in the NPP's. The temperature fluctuations induce a reliability reduction of the nuclear components. In France in may 1998, damages were occurred in a mixing tee from the heat removal system (RHRS) in the Civaux Nuclear Power Plant. A wide experimental program produced by AREVA ANP, CEA, and EDF was initiated to study the thermal fatigue phenomena in the mixing tees. A tee mock-up in 304L stainless steel material and geometrically close to the industrial component were designed to submit a severe endurance test impacted by realistic turbulent mixing of two fluids at large gap of temperature. A large facility, called FATHER, was implemented to supply the necessary power for endurance test performing. A second stage was to set measurements in the fluid and in the wall with specific instrumentation (flux meters) to assess the thermal load which leads the potential damages in the inner surface. This paper presents the experiment and the significant results from the endurance and thermal hydraulic tests. The mean and fluctuating temperature are plotted in the mixing area in the wall and in the fluid close to the wall. Helped by inverse method, the wall temperature can be assessed. The heat transfer in the wall, assumed as 1D is qualified and the key parameters which influence the level of temperature fluctuation as the velocity mixture, the flow rate ratio and the difference of temperature are evaluated. At last, to complement the experiment, a numerical analysis using TRIO U code was performed within the large eddy simulation approach for the specific geometry of the FATHER mock up.

Heat-transfer and temperature-defect laws in a turbulent boundary layer on a plate with injection

For a thermal turbulent boundary layer on a permeable flat plate, similarity laws for the heat flux at the wall and flow temperature are established. According to the universal temperature-defect law, the profiles of this quantity for any injection and sufficiently large Reynolds numbers everywhere outside the viscous sublayer may be described by a single curve, which is known from experimental data for an impermeable plate. The universal heat-transfer law in the form of the generalized Reynolds analogy allows one to represent the heat flux distributions that correspond to various Reynolds numbers and various injection velocities as a function of one variable. The results are obtained without the formulation of special closure hypotheses. 1. We consider an incompressible heat-conducting turbulent boundary layer flow over a smooth flat plate in a uniform stream with constant velocity U e and temperature θ e . The transpiration (injection or suction) velocity v w directed along the normal to the surface and the temperature on the wall θ w are also considered to be constant. The turbulent flow is assumed to develop directly from the leading edge of the plate. We also assume that the level of velocity and temperature fluctuation in the free stream is negligibly small and does not affect the flow and heat transfer in the boundary layer. Temperature is treated as a passive contaminant exerting no influence on the liquid motion.