Momentum Balance Model Research Articles

Application of a particle, momentum, and energy balance model to calculate the structure of the edge pedestal in DIII-D

A calculation of edge density and temperature profiles based on “classical” physics—particle, momentum, and energy balances, heat conduction closure relations, and neutral particle transport—yielded a pedestal structure that is qualitatively and quantitatively similar to that found experimentally in five DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharges, when experimental radial electric field and rotation profiles and experimentally inferred heat transport coefficients were used. The principal cause of the density pedestal was a peaking of the inward pinch velocity just inside the separatrix caused by the negative well in the experimental electric field, and the secondary cause was a peaking of the radial particle flux caused by the ionization of incoming neutrals. There is some evidence that this peaking of the radial particle flux just inside the separatrix may also be responsible in part for the negative electric field in that location.

Mass and Momentum Balance Model of a Mixed Flowing/Powder Snow Avalanche

This work uses a one-dimensional, depth averaged model to compute the massbalance of a mixed flowing/powder snow avalanche. This model is comprisedof three basic components: the dense flowing avalanche, the powder cloud anda turbulent wake. The dynamics of a mixed avalanche is strongly dependent onthe interaction between the components and also on the snow cover and ambientair, in particular the exchange or entrainment of snow and air mass. Therefore, animportant first step for modelling mixed avalanches is a basic understanding of thenature of these mass exchanges. In this paper, the governing equations of mass,momentum and turbulent energy are briefly presented. Numerical simulations wererun for three avalanche tracks – Aulta, Galtur and Vallee de la Sionne – for whichdata from real snow avalanche events exist. Based on the results, conclusions weredrawn regarding the parameterisation of the mass exchanges. The mass balances forthese three contrasting avalanches are presented.

F215 滞留部の熱成層化による高サイクル熱疲労に関する研究 : L_1 評価手法の概要

There are a lot of types of branch pipes with a closed end in a nuclear power plant. At a branch pipe connected to a main such as a main coolant pipe, there is temperature gradient in the layer between the cavity flow and the colder fluid by heat removal. It is necessary to evaluate the structural integrity of a pipe in the front of the cavity flow and to establish the piping design standard. In the piping design standard, there are the maximum penetration length (L_1) and the minimum one (L_2) in order to avoid the elbow between L_2 and L_1. The L_1 evaluation method is shown in the present report. The method is based on the momentum balance model by defining the boundary layer coefficient. The method reproduced the penetration length by cavity flow in several types of the vertical pipes within 10% accuracy. The piping design standard is going to be established by using the method.

Electrostatic Fluxes and Plasma Rotation in the Edge Region of EXTRAP-T2R

The EXTRAP-T2 reversed field pinch has undergone a significant reconstruction into the new T2R device. This paper reports the first measurements performed with Langmuir probes in the edge region of EXTRAP-T2R. The radial profiles of plasma parameters like electron density and temperature, plasma potential, electrical fields and electrostatic turbulence-driven particle flux are presented. These profiles are interpreted in a momentum balance model where finite Larmor radius losses occur over a distance of about two Larmor radii from the limiter position. The double shear layer of the E×B drift velocity is discussed in terms of the Biglari-Diamond-Terry theory of turbulence decorrelation.

Experimental measurements and modelling of the structure of the radial electric field in RFX

The experimental determination of the radial electric fieldEr and the associatedE ×B drift velocity at the edge of RFX is presented and possible mechanisms responsible for its generation are discussed.Er measurements by means of an array of Langmuir probes and those deduced from Doppler spectroscopy of impurity lines agree fairly well. In particular the rotation velocity of the plasma edge has been determined from the Doppler shift of a C III emission line. The observation of other ions characterised by different radial positions, such as B IV and C V, has allowed an estimate of the velocity shear. Typical values of plasma rotation at the edge are around 10 km/s while the velocity shear is of the order of (105−106)s−1 in the spontaneous layer, a few cm thick, usually observed in standard discharges. Plasma rotation has been artificially modified by both positive and negative edge biasing and the associated increase or decrease of the fluid velocity is well in agreement with the radial electric field change. The modification ofEr during edge biasing and Pulsed Poloidal Current Drive (PPCD) are also reported and interpreted within a momentum balance model. Analytical and self-consistent Monte Carlo models at the plasma edge suggest that impurities have a relevant role in the generation of the radial electric field, due to their relatively large Larmor radius.

Extensional rheology of concentrated poly(ethylene oxide) solutions

The shear and extensional rheology of three concentrated poly(ethylene oxide) solutions is examined. Shear theology including steady shear viscosity, normal stress difference and linear viscoelastic material functions all collapse onto master curves independent of concentration and temperature. Extensional flow experiments are performed in fiber spinning and opposed nozzles geometries. The concentration dependence of extensional behavior measured using both techniques is presented. The zero-shear viscosity and apparent extensional viscosities measured with both extensional rheometers exhibit a power law dependence with polymer concentration. Strain hardening in the fiber spinning device is found to be of similar magnitude for all test fluids, irrespective of strain rate. The opposed nozzle device measures an apparent extensional viscosity which is one order of magnitude smaller than the value determined with the fiber spinline device. This could be attributed to errors caused by shear, dynamic pressure, and the relatively small strains developed in the opposed nozzle device. This instrument cannot measure local kinematics or stresses, but averages these values over the non-homogenous flow field. These results show that it is not possible to measure the extensional viscosity of non-Newtonian and shear thinning fluids with this device. Fiber spin-line experiments are coupled with a momentum balance and constitutive model to predict stress growth and diameter profiles. A one-mode Giesekus model accurately captures the plateau values of steady and dynamic shear properties, but fails to capture the gradual shear thinning of viscosity. Giesekus model parameters determined from shear rheology are not capable of quantitatively predicting fiber spinline kinematics. However, model parameters fit to a single spinline experiment accurately predict stress growth behavior for different applied spinline tensions.

Dynamics of a Radially Rotating Beam With Impact, Part 2: Experimental and Simulation Results

A theoretical and computational model to study the dynamics of a radially rotating beam with impact were presented in Part 1. In this paper the experimental results are presented and they are compared with simulations using the momentum balance model described in Part 1. Excellent agreement was found between the experiments and simulation. Sensitivity studies were employed to show that the model is applicable for a fairly wide range of parameter values. Thus, the momentum balance method has been demonstrated to be capable of accurately predicting the dynamics of systems which consist of rigid and elastic links undergoing impact.

Holdup of fine particles in the fluidized dense bed of the multisolid pneumatic transport bed

Experiments were performed to determine the holdup of fine particles in the fluidized dense bed of the multisolid pneumatic transport bed. The holdup was found to increase with increasing coarse particle density and decreasing coarse particle diameter. Holdup also increased with increasing fine particle diameter. A momentum balance model was utilized to characterize the fine particle holdup behavior, based on an interaction coefficient for collision between fine particles and coarse particles. This interaction coefficient was found to be significantly lower for the turbulent regime of the dense bed than for the slugging regime. The interaction coefficient decreased with coarse particle diameter. The momentum balance model, using the empirically correlated interaction coefficient, was found to satisfactorily account for the fine particle holdup in the slugging dense bed.