Function Of Pertinent Parameters Research Articles

One-dimensional narrow-band conductors

We review one-dimensional lattice models and the corresponding results that describe the low-temperature properties of quasi-one-dimensional lattice systems with long-range interaction. A widely known example is narrow-band low-dimensional conductors with long-range interelectron repulsion. The models deal with particles that live on the one-dimensional host lattice (chain), translation invariant or disordered, and interact via the long-range repulsive potential. The results are presented concerning the translation invariant host chain, in particular: the low-temperature thermodynamics incommensurable ground states and related devil-staircase form of various characteristics as functions of pertinent parameters, the self-localization of particles, a new branch of elementary excitations, etc. In the disordered case, where the sites of the host chain fluctuate randomly around the sites of the periodic chain, the low-temperature thermodynamics and the structure of the ground state are discussed in the framework of a certain model, which we call the cluster model and which seems to be a fairly reasonable approximation for low temperatures and small concentration of particles. Using analytical and numerical tools we analyze the thermodynamics and the ground state of the model. The latter proves to be a sequence of random domains and we study in detail their distribution.

Rapid Wear Modelling in a Slurry Pump Using Soft 3D Impeller Material

Slurry transport systems are often limited in run length by the life of the pump internals, especially the impeller. The present work investigated abrasive wear of the impeller of a Hayward Gordon XR2(7) Torus Recessed Impeller slurry pump in a flow loop. The stock stainless steel impeller was replaced by a set of plastic test impellers with the same nominal geometry, fabricated by additive manufacturing (3D printing). A parametric set of abrasive wear experiments was conducted at five pump rotational speeds and three solid concentrations of garnet slurry in a pipe flow loop. Pump performance tests were conducted using impellers with progressive wear conditions, to investigate how a worn impeller affects hydraulic power delivery. A parabolic fit was imposed to describe the relationship between head and flow rate, and an empirical model was proposed to predict the pump head with damaged impellers. When the rotational speed is high, the damaged impeller has a larger effect on the pump’s performance than when the rotational speed is low. The head difference between the undamaged impeller and a 7.62%-mass-loss damaged impeller was 1.5 m at 1750 rpm rotational speed, however, for 850 rpm, the head difference was 1 m. Implications for pump diagnostics in other types of systems are discussed. This experiment gives a method for rapidly assessing wear locations, and provides a tool to predict wear rates on harder materials if scaling parameters are available. This first attempt at a scaling law is not reliable enough to accurately predict the wear rate for specific conditions, but shows the relative wear as a function of pertinent parameters.

Effect of thermophoresis on the motion of aerosol particles in natural convective flow on horizontal plates

The present work investigates the effects of thermophoresis and transverse magnetic field on aerosol particle transport and deposition onto a horizontal plate in the presence of a natural convective flow. Micro to nano sized particles (particle diameter in the range 1nm–1μm) are considered. A similarity solution for the fluid flow field is formulated for natural convection with and without magnetohydrodynamic (MHD) effects above a heated horizontal plate as well as beneath a cold horizontal plate. The mechanisms of particle deposition include the effects of free convection, Brownian diffusion and thermophoresis. Numerical results for the velocity and temperature fields of the fluid, and, the concentration profile and the deposition velocity of the particles are obtained and presented graphically as a function of pertinent parameters. The importance of Cunningham correction on the concentration profile and deposition velocity of ultrafine (sub-micron to nanometer) particles is demonstrated. It is found that the thicknesses of both the hydrodynamic boundary layer and thermal boundary layer increase with an increase in magnetic field parameter. The deposition velocity decreases with an increase in particle diameter dp (i.e an increase in particle Schmidt number Sc), usually decreases with an increase in magnetic field parameter ζ, and increases with an increase in the value of the coefficient of diffusion due to temperature gradient DT. It is shown that for the cold plate facing downward, the thermal drift of particles assists Brownian diffusion. For the heated plate facing upward, the thermal drift away from the surface decreases the overall deposition velocity which decreases drastically above a certain particle size.

Finite Horizontal Well Crossing a Natural Fracture Normally

Summary An analytic solution in terms of the Laplace transformation is presented to calculate the pressure distribution in multizone, composite reservoirs intercepted by a finite horizontal well that is oriented normal to the plane interfaces in an infinite field. A three-zone reservoir is analyzed for illustrative purposes, with the horizontal well traversing a thin high-permeability central zone confined between two parallel planes representing the natural fracture, and with the well completed in the adjacent zones. The method provides the transient pressure field for each of the three zones, allowing analyses of the flow fields both within the fracture and within the reservoir as a function of pertinent parameters. The computational scheme considered is both viable and robust. To our knowledge, this topic is yet to be analyzed in this fashion analytically. The numerical results presented are limited to a parametric study of (1) transient well pressures and their time derivative and (2) steady-state flux and flow-rate distributions at the fracture faces as a function of distance from the well. A steady-state correlation of the productivity index is also provided. We discovered that of the two generally accepted procedures for estimating the average well pressure, the one based on well rates proportional to the local permeability and well length gives results consistent with our model, whereas the one requiring equal average pressure at each well segment introduces significant disturbances to the flow field near the fracture-well intercepts, at least when small and large well lengths are present, as is the case in the problem under consideration. This subject needs additional investigation.

Modeling surfactant removal in foam fractionation: I — Theoretical development

Surfactant removal by foam fractionation was theoretically analyzed by treating surfactant mass transfer from a bulk solution onto a moving bubble as a convective diffusion process. A mathematical model expressing the removal rate as a function of pertinent parameters was developed. The parameters included superficial air velocity, bubble size, bubble rising velocity, surfactant diffusion coefficient, and concentration. The model indicated that surfactant removal can be described as a first-order process whose rate increases with the diffusion coefficient, the superficial air velocity and the surfactant concentration in the bulk solution, but decreases with bubble size and bubble rising velocity. Based on the assumption of a completely mixed reactor within a section of a foam fractionator, a simplified model for foam fractionation under batch operation conditions was also presented. This simplified model provides a theoretical basis according to which the diffusion coefficient of surfactants can be determined and the model itself can be verified with experimental data.

The magnetic stability of face-cooled composite tape superconductors

The concept of face-cooled composite tape is proposed to stabilize high critical current densities in Nb/sub 3/Sn, V/sub 3/Ga, and oxides. The stability is promoted by the combined action of the dynamic stability and the transient cryogenic stability. The expression of the limiting current density of stability is derived as a function of pertinent parameters of the superconductor, stabilizing normal metal, and coolant. An experimental proof of the analysis is given for an Nb/sub 3/Sn-Cu system. The specimens are made by alternately stacking strips of Nb/sub 3/Sn and copper. Stability is estimated by observing flux jumps for specimens of different thicknesses of copper. The experimental results agree well with the analysis. and an overall current density of about 500 A/mm/sup 2/ is stabilized. The concept of face-cooled composite tape will offer a useful basic criterion in designing conductors of high-T/sub c/ oxides.

Quasi-Static Analysis of Foil Journal Bearings for a Brayton Cycle Turboalternator

A quasi-static analysis is presented for foil journal bearings designed for a NASA Brayton Cycle Turboalternator. Included in the analysis are effects of “slack” (due to flexural rigidity of the foil), of frictionally restrained extension of the foil-length in contact with cylindrical guides, of fluid inertia and compressibility, and of thermal expansion of rotor, foil and supporting structure. Comparisons are made with results of early experiments performed by Licht [1, 2] and recent data of Licht and Branger [6, 7]. Variations of film thickness, foil tension and bearing stiffness are presented graphically as functions of pertinent parameters for the case of operation in zero-gravity environment.