Rate Of Energy Transport Research Articles

Characteristics of the wind regime north of Jubail, Saudi Arabia, based on high resolution wind data

An analysis of regional wind data was based on the measurements of two weather stations for a period of 2 years. Ten-minute mean values where based on readings in 10-s intervals. In the study, wind direction and sand drift potential were considered. During the course of 1 year six different wind regimes occured: (1)a high energy Mediterranean north-west regime from November to February; (2)a bimodal cyclonic end-phase in March; (3)a moderate eastern spring phase in April; (4) a complex transition phase in May; (5)a high energy summer Shamal regime from June to August; and (6)a low energy autumn phase in September and October. Concerning sand movement potential, two of the phases are not relevant, two show bimodal or complex patterns, and two significantly dominate sand movement from north to south. The summer high energy regime coincides with the unfavourable season for plant growth and thus the lowest vegetation cover. Regarding the actual sand drift the Eastern Province of Saudi Arabia is influenced by a unimodal wind regime causing a sand flow from the north areas to the south. There is an over-all decrease in wind energy and sand transport rates, so that accumulation dominates in the southern Jafurah and northern Rub'al Khali. Vegetation characteristics and geomorphological features indicate the amount of actual sand dynamics in the study area. According to such observations and conventional meteorological data, the Eastern Province can be divided into three regions: (1)a sand source region in the north which increases due to a continuing reduction of the vegetation cover; (2)a transport zone where sand input from the north equals sand output to the south, and (3)the accumulation zone in the south which shows a positive sand budget.

Does “τ≈1” Terminate the Isothermal Evolution of Collapsing Clouds?

We examine when gravitationally collapsing clouds terminate their isothermal evolution. According to our previous work, the condition with which isothermality is broken down is classified into three cases, i.e., when (1) the compressional heating rate overtakes the thermal cooling rate, (2) the optical depth for thermal radiation reaches unity, or (3) the compressional heating rate becomes comparable with the energy transport rate because of radiative diffusion. In the present paper this classification is extended to more general values of the initial cloud temperature Tinit and opacity κ, and we determine the critical densities with which these conditions are satisfied. For plausible values of Tinit and κ, we find that the isothermal evolution ceases when case 1 or 3 is satisfied, and case 2 has no significance. We emphasize that the condition of τ≈1 never terminates isothermality, but nonisothermal evolutions begin either earlier or later depending on the initial temperature and opacity. This result contrasts with the conventional idea that opaqueness breaks isothermality. On the basis of the critical density discussed above, the minimum Jeans mass for fragmentation, MF, is reconsidered. In contrast to the results by previous authors that MF is insensitive to Tinit and κ, we find that MF can be substantially larger than the typical value of ~10-2 M☉ depending on Tinit and κ. In particular, MF increases with decreasing metallicity, MF∝κ−1, for low-metal clouds. A cloud with κ=10−4 cm2 g-1 and Tinit=10 K yields MF=3.7 M☉. Finally, our critical densities would be helpful for hydrodynamic simulations that are intended to simply handle the hardening of the equation of state.

Electron energy balance in an ionization-unstable plasma in a magnetogasdynamic channel

An experimental investigation was made of the evolution of ionization instability in a model of a disk-shaped Faraday magnetogasdynamic channel connected to a shock tube in a pure rare gas (xenon) with an alkaline additive. The main components of the average electron energy balance were determined: the Joule heating power, the average rate of energy transport of the heavy component by elastic collisions, and the average rate of energy lost through ionization. It was found that the electron energy defect which includes losses not taken into account, increases abruptly at supercritical values of the magnetic induction and accounts for approximately half of the Joule heating power. It is concluded that some of the electron energy is transferred to pulsations.

A Model of Turbulent Mixing of Species, Momentum, and Energy in a Vapor Shield Plasma

Evidence suggests that turbulent mixing may affect the energy transport through the vapor shield (VS) formed during a tokamak disruption. The VS is first found to be very unstable according to the Rayleigh-Taylor stability criteria. Adding beam mass to the vaporized material and then mixing of the entire VS is found to cause a significant increase in energy transport through the VS for fusion reactor disruption-relevant energy beams. Mixing the VS for electrothermal gun-relevant energy beams can also affect the energy transport rate, depending on the source species used.

Bi-Sb semiconductor alloy synthesized by mechanical alloying

This work reports the electrical and thermal transport properties of polycrystalline Bi1-xSbx (x=0.10 and 0.14) pellets in the temperature range of 20−300K. The pellets were prepared by spark plasma sintering from ball-milled Bi1-xSbx powders. As semiconductor, the samples displayed n-type conductivity as indicated by the negative sign of the Seebeck coefficient. Semiconducting properties were observed for the Bi0.86Sb0.14 alloy in the entire temperature range of 20−300K, whereas the Bi0.90Sb0.10 alloy exhibited metal-like behavior at low temperatures (20−120K) and semiconducting one at temperatures between 160K and 300K. The metal-like feature of the Bi0.90Sb0.10 sample was attributed to the electron conduction by means of topologically protected surface gapless states, as this material has been reported to be a 3D topological insulator. The temperature dependence of the scattering coefficient and Fermi level shift were analyzed, assuming that prepared alloys are non-degenerate semiconductors in the temperature range where their semiconducting behavior was observed. The carrier thermal conductivity was estimated from the Lorenz number and Wiedemann-Franz law. At high temperature, the thermal energy transport rate is similar for both alloys, whereas at low temperature, it depends on the characteristic electrical behavior of each sample. Interestingly, the polycrystalline nature of our samples seems not affect their electrical and thermal transport properties.

Rate of energy transport and arrival times in pulse propagation in a waveguide

The concept of group velocity has one of three origins and is described in terms of a mathematical construct to predict arrival times in pulse propagation in a waveguide, particularly within the context of normal mode theory. Under certain conditions, group velocity can lead to confusion. On the other hand, the rate of energy transport, which is what one really seeks, may be derived by taking the ratio of the mean energy flux through a vertical section with the energy density between two planes separated by a wavelength. In the context of normal mode theory, this leads to an integral expression that involves the normalized vertical wavefunctions and the velocity profile leading to a physically appealing expression that lends insight to expected modal arrivals. Under certain conditions, it leads to the same results as the group velocity concept: It can be calculated with only one frequency and is valid near cutoff frequencies. This supplies one with an integral expression for a velocity that better characterizes arrival times of packets of energy. [Work sponsored by ONR, the Naval Research Laboratory, and the University of New Orleans.]

FUEL VAPOR ACCUMULATION EFFECT ON THE COMBUSTION CHARACTERISTICS OF MULTICOMPONENT FUEL DROPLETS

The effect of fuel vapor accumulation on the gasification behavior of a multicomponent fuel droplet has been investigated. Expressions for the droplet vaporization rate, flame front standoff ratio and other quantities of interest have been obtained by using a formulation that considers quasi-steady, diffusive-convective transport in the gas phase, and transient diffusive transport within the droplet. Results are presented for the combustion of a bicomponent heptane-decane fuel droplet. It is demonstrated that a significant amount of fuel vapor can be accumulated in the inner zone to the flame, which has a noticeable effect on the droplet gasification behavior since the fuel consumption rate is reduced compared to the vaporization rate. This has important implication for spray flames using multicomponent fuel droplets, since the fuel vapor accumulation can substantially modify the rates of interphase energy and mass transport rates, as well as the fuel vapor distribution in the flow field. Results also indicate that the fuel accumulation effect, combined with the effect of high liquid mass diffusional resistance (large Lewis number), leads to a self-sustained oscillation of the vaporization rate. The oscillation is unique to the multicomponent fuel droplet in that the accumulation effect does not cause any oscillation for a pure fuel droplet. The oscillatory behavior is also suppressed for a multicomponent fuel droplet for moderate values of liquid Lewis number with the accumulation effect, and for any values of liquid Lewis number without the accumulation effect.

Approach to Equilibrium in Accelerated Global Oceanic Models

The approach to equilibrium of a coarse-resolution, seasonally forced, global oceanic general circulation model is investigated, considering the affects of a widely used acceleration technique that distorts the dynamics by using unequal time steps in the governing equations. A measure of the equilibration time for any solution property is defined as the time it takes to go 90% of the way from its present-value to its equilibrium value. This measure becomes approximately time invariant only after sufficiently long integration. It indicates that the total kinetic energy and most mass transport rates attain equilibrium within about 90 and 40 calender years, respectively. The upper-ocean potential temperature and salinity equilibrium times are about 480 and 380 calender years, following 150- and 20-year initial adjustments, respectively. In the abyssal ocean, potential temperature and salinity equilibration take about 4500 and 3900 calender years, respectively. These longer equilibration times are due to the slow diffusion of tracers both along and across the isopycnal surfaces in stably stratified regions, and these times vary with the associated diffusivities. An analysis of synchronous (i.e., not accelerated) integrations shows that there is a complex interplay between convective, advective, and diffusive timescales. Because of the distortion by acceleration of the seasonal cycle, the solutions display some significant adjustments upon switching to synchronous integration. However, the proper seasonal cycle is recovered within five years. Provided that a sufficient equilibrium state has been achieved with acceleration, the model must be integrated synchronously for only about 15 years thereafter to closely approach synchronous equilibrium.

Diffuse wave energy transport in multicoupled, one-dimensional Anderson localizing systems

The spatial and time domain evolution of energy density in a multicoupled, one-dimensional disordered system is investigated. Scaling theory predictions are presented for both localization lengths and rates of diffuse transport. Scaling arguments suggest that localization lengths equal πρDo, where ρ is the modal density per unit length and Do is the bare diffusivity. Additionally, the rate of diffuse energy transport over a distance L is found to scale as ρL. These predictions are compared with the behavior of a numerical model for an Anderson localizing system. The system modeled is a cylindrical membrane disordered by the introduction of a random foundation of springs. [Work supported by ONR.]

Core to surge-line energy transport in a severe accident scenario

The analysis of loss-of-coolant accidents in a nuclear power plant, which progress to the stage where the core is uncovered, poses important safety related questions. One of these questions concerns the rate of energy transport to metal components of the primary system. An experimental program has been conducted at the University of Maryland test facility which quantifies the rate of energy transfer from an uncovered core in a B&W plant (once-through type steam generators). SF 6 is used to simulate the high pressure steam at prototypical conditions. A time-dependent scaling methodology is developed to transpose experimental data to prototypical conditions. To achieve this transformation, a nominal fluid temperature increase rate of 1.0 °C s −1 is inferred from available TMI-2 event data. To bracket the range of potential prototypical transient scenarios, temperature ramps of 0.8 °C s −1 and 1.2 °C s −1 are also considered. Repeated tests, covering a range of test facility conditions, lead to estimated failure times at the surge line nozzle of 1.5–2 h after initiation of the natural circulation phase of the transient.

Study on Multiple-Time-Scale Reynolds Stress Model. 2nd Report. Verification for Grid Turbulence.

Conventional turbulence models have a single time scale of turbulence. Therefore, they cannot predict the flows that are influenced by many time scales of turbulence. In simulating such flows it is neccessary to introduce some information about the scales of turbulence. In order to overcome this problem, I proposed a multiple-time-scale Reynolds model and the model coefficients were deter-mined for a grid turbulent flow. In this study, the model was applied to a variety of grid turbulent flows to verify the model performance. The numerical results for turbulent energy, Reynolds stresses and second and third invariants were compared with the experimental data. The temporal change of large and small-scale conponents for Reynolds stresses and energy transport rates were also verified. It was found that the model can satisfactorily predict a wide range of grid turbulent flows. In addition, it was verified that the method used in setting initial conditions is reasonable.

Properties of the Oort cloud and the origin of comets

We report the results of an N-body simulation with 100 stars in the solar neighbourhood and 400 Oort cloud bodies to determine the internal structure and stability of the Oort cloud and to show various physical processes revealing the formation of comets from the Oort cloud. Effects due to Jupiter and Saturn as well as local vertical oscillation of the Solar system within the galactic disc are also included. We follow the evolution of the Oort cloud and the stars for 1.6 × 108 yr, both with and without the planets. We reproduce the shape of the observed 1/a distribution for the comets. We determine the evolution of the number density of the cloud. The perturbation due to the planets causes fluctuation in the number density at both the inner and the outer edges of the Oort cloud. The stellar encounter also causes some fluctuation, mostly at the outer edge. In general, the Oort cloud appears to be very stable under stellar perturbations, with a half-life well beyond 3 million years. We obtain the energy transport rate to the clouds. This result agrees well with existing analytical results.

Acoustic Bloch wave energy transport and group velocity

The relationship between the steady‐state rate of energy transport and the group velocity is investigated for acoustic Bloch waves in a periodic waveguide. A time‐average energy flux relation is derived and used to find the energy transport velocity for an arbitrary periodic waveguide. An apparent disparity between the energy transport velocity and the power delivery is discussed. The group velocity is derived using a Bloch wave generalization of the usual Fourier transform method and is shown to be equal to the rate of energy transport. The integral transform method works well for the boundary value problem as the associated Bloch wave transform is relatively straightforward. The initial value problem, however, involves the inverse Bloch wave transform, the problems associated with which are discussed. [Work supported by the Office of Naval Research.]

Neoclassical transport of energetic minority tail ions generated by ion-cyclotron resonance heating in tokamak geometry

Neoclassical transport of energetic minority tail ions, which are generated by high-powered electromagnetic waves of the ion cyclotron range of frequencies (ICRF) at the fundamental harmonic resonance, is studied analytically in tokamak geometry. The effect of Coulomb collisions on the tail-ion transport is investigated in the present work. The total tail-ion transport will be the sum of the present collision-driven transport and the wave-driven transport, which is due to the ICRF-wave scattering of the tail particles as reported in the literature. The transport coefficients have been calculated kinetically, and it is found that the large tail-ion viscosity, driven by the localized ICRF-heating and Coulomb slowing-down collisions, induces purely convective particle transport of the tail species, while the energy transport is both convective and diffusive. The rate of radial particle transport is shown to usually be small, but the rate of radial energy transport is larger and may not be negligible compared to the Coulomb slowing-down rate.

Candidate mode for electron thermal energy transport in multi-keV plasmas

The linear and quasilinear theory of the collisionless trapped electron mode (also called the ‘‘ubiquitous’’ mode) is analyzed, in order to illustrate its possible role in the electron thermal energy transport observed in magnetically confined plasmas. This instability is driven by the combined effects of the plasma pressure gradient (which includes the contributions from the temperature gradients of ions and electrons) and of the local magnetic curvature drift of trapped electrons and of circulating and trapped ions. Depending on the value of its wavelength across the magnetic field, this mode can connect with a branch of the ion temperature gradient instability, provided the ion temperature gradient is sufficiently strong. Also, under certain conditions, it can be driven unstable solely by a combination of electron temperature gradient and Landau damping by trapped electrons. The relevant modes are found to be robust against variation of parameters such as the electron collisionality, and to be consistent candidates in order to explain the experimentally observed rate of electron thermal energy transport from the center of the plasma column.

Diffusion-controlled startup of a gas-loaded liquid-metal heat pipe

Liquid-metal heat pipes have exhibited difficulties starting up from a frozen-state. Inert gas loading is a possible solution to the frozen-state startup problem. The present study deals with the diffusion-controlled startup analysis and testing of an argon-loaded, 2-m-long, stainless steel-sodium heat pipe of the double-walled type with artery channel and long adiabatic section. A two-dimensional, quasi-steady state, binary vapor-gas diffusion model determined the energy transport rate of vapor at the diffusion front. The analytical solution to the diffusion problem provided the vapor flux, which in turn was used in the one-dimensional transient thermal model of the heat pipe to predict the time rate-of-change of temperature and position of the hot front. The experimental test results successfully demonstrated the startup of a gas-loaded sodium heat pipe and validated the diffusion model of the startup. 17 refs.

STUDY OF SHELF WAVES VS SAND DRIFT IN NW COAST OF TAIWAN

For the planning and design of harbor and coastal Engineering, most important affected factors are waves and Littoral drift. This research deals with analysis of the measured waves and the budget of the beach material whether it is deposited or scoured in the North-western coast of Taiwan; and the relationship between wave energy and littoral transport rate. For processing this research the field Survey wave measurement, sand sampling, and echo sounding is necessitated. The objective of this research is to establish the model of waves and littoral transport budget. Therefore, the results of this research are planned to submit to the planning and design of harbor and coastal engineering works of the Taiwan west sandy coast. The main contains of this research are consisted of (1) Analysis, observations and investigations of the field oceanographic data, winds, waves, coastal geomorphology and littoral drift of the North-western coast of Taiwan. (2) Analysis of the shelf waves from the actual measured wave records. (3) Research of the wave decaying process of the continental shelf waves. (4) Statistical research of the measured waves and establishment of the practical model of the relationship between the shelf wave energy and the littoral transport rate in the north-west coast of Taiwan.

Comparison between experiment and theory

In the idealized theory of toroidal magnetic confinement, the plasma is supposed to be embedded in a nested set of topologically toroidal magnetic surfaces. The plasma is assumed to be stable so that all transport processes, such as thermal conduction, are determined only by Coulomb collisions between the particles. In this paper, we first compare the experimental results with the predictions of this theory. The actual energy transport rate is found to be much higher than that predicted. This is believed to be due to instability processes in the plasma although there remains the possibility that the idealized or classical theory is not complete. The role of electrostatic and of magnetic instabilities is discussed. Finally, the consequences of a simple model, in which the form of the temperature profile is fixed, are discussed.

Winds and sand movements in the Namib Sand Sea

AbstractWind regimes in the vicinity of the Namib Sand Sea are high energy unimodal near the coast, becoming bimodal or complex inland. There is an overall decrease in wind energy and sand transport rates from south to north and west to east, such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea. Such a pattern can explain much of the observed spatial variability in dune types, sizes, and sediment characteristics and lends support to a climatic model of sand sea formation in this region.Seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport, most of which is generated by winds of moderate velocity and frequency.

Hot electrons and energy transport in metals at millikelvin temperatures.

Using a new technique, we measure the energy-loss lifetime for electrons in a metal from 25 to 320 mK. Applying a small electric field, of order 1 μV/cm at 25 mK, causes carriers to heat above the temperature of the phonon bath. The temperature difference induced reflects the rate of energy transport between the electrons and lattice. The 1-ms energy-loss lifetime and 1-cm inelastic diffusion length we have measured at 25 mK are the largest ever obtained.