Analysis Of Energy Transport Research Articles

Energy transport analysis in ultrashort pulse laser ablation through combined molecular dynamics and Monte Carlo simulation

Mechanisms of energy transport during ultrashort laser pulses (USLPs) ablation are investigated in this paper. Nonequilibrium electron-transport, material ionization, as well as density change effects, are studied using atomistic models---the molecular dynamics (MD) and Monte Carlo (MC) methods, in addition to the previously studied laser absorption, heat conduction, and stress wave propagation. The target material is treated as consisting of two subsystems: valence-electron system and lattice system. MD method is applied to analyze the motion of atoms while MC method is applied for simulating electron dynamics and multiscattering events between particles. Early-time laser-energy absorption and redistribution as well as later-time material ablation and expansion processes are analyzed. This model is validated in terms of ablation depth, lattice/electron temperature distribution as well as evolution, and plume front velocity, through comparisons with experimental or theoretical results in literature. It is generally believed that the hydrodynamic motion of the ablated material is negligible for USLP but this study shows it is true only for its effect on laser-energy deposition. This study shows that the consideration of hydrodynamic expansion and fast density change in both electron and lattice systems is important for obtaining a reliable energy transport mechanism in the locally heated zone.

Analysis of Atmospheric Energy Transport in ERA-40 and Implications for Simple Models of the Mean Tropical Circulation

Abstract An analysis of atmospheric energy transport in 22 years (1980–2001) of the 40-yr ECMWF Re-Analysis (ERA-40) is presented. In the analyzed budgets, there is a large cancellation between divergences of dry static and latent energy such that the total energy divergence is positive over all tropical oceanic regions except for the east Pacific cold tongue, consistent with previous studies. The west Pacific and Indian Oceans are characterized by a balance between diabatic sources and mean advective energy export, with a small eddy contribution. However, in the central and eastern Pacific convergence zone, total energy convergence by the mean circulation is balanced by submonthly eddies, with a small diabatic source. Decomposing the mean advective tendency into terms due to horizontal and vertical advection shows that the spatial variation in the mean advection is due largely to variations in vertical advection; these variations are further attributed to variations in the vertical profile of the vertical velocity. The eddy energy export, due almost exclusively to eddy moisture export, does not exhibit any significant seasonal variation. The relationship between the eddies and the mean circulation is examined. Large-scale moisture diffusion is correlated with eddy moisture export on (500 km)2 spatial scales, implying that eddy activity preferentially dries narrow convergence zones over wide ones. Eddy moisture export is further linked to the depth of mean convection in large-scale convergence zones with larger eddy export associated with shallower circulations. This suggests a mechanism that could contribute to the observed variation in mean divergence profiles across the northern tropical Pacific whereby sea surface temperature gradients set the width of convergence zones and eddy activity modulates the tropospheric relative humidity and divergence profile. The importance of variations in the vertical profile of the vertical velocity and eddies in closing the energy budget implies that simple models of the mean tropical circulation should include these effects.

Numerical analysis of energy transport by intense resonance line in Lithium plasmas

Energy transport by a strong resonance line like Lyman α has been studied numerically. The corona region of laser-produced Li plasmas is assumed to be the isothermal expansion model. As a result, though the peak intensity of Lyman α keeps Planckian value, width of the line becomes broader during the transmission in the corona region. If the optical depth could be controlled thicker much more than unity, available power exceeds the value of surface area x intensity of Planckian x line width of emissivity, and the EUV light source for the semiconductor lithography can be designed by Li target.

Turbulence structure in the vortex formation region behind a circular cylinder in lock-on conditions

The present experimental research has been undertaken in order to explain to what extent the turbulent structure of the flow around a stationary rigid cylinder may be affected by an oscillating approach flow. The general aim was to establish a direct link between the oscillating inflow, local time-resolved quantities like skin friction and surface pressure and near wake behaviour behind the circular cylinder. It has been confirmed that the lock-on synchronization between the periodicity of vortex shedding and free stream oscillations is an important factor affecting the formation mechanisms of the wake. In particular it was found that periodical inflow disturbances bring about a rapid growth of pressure and wall shear stress fluctuations near the separation point. The present results revealed also a tendency toward the shortening of vortex formation length and significant growth of the time and linear microscales of turbulence in lock-on conditions. Additional evidence concerning the role of inflow periodical disturbances in the near wake modification was obtained from analysis of turbulent kinetic energy transport in the flow.

Systematic studies of pulse propagation in ducted oceanic waveguides in normal mode representation

Acoustic pulse propagations in typical environments of the Gulf of Mexico and Yellow Sea are modeled by a new normal mode code, SWAMP, and compared to the experimental data. The presence of the seasonal surface duct in the ocean is confirmed to be responsible for the generation of a unique set of modes forming the so-called “Precursor Phenomenon” first discovered by DeFerrari and Monjo. It is shown that the conventional theory of group velocity fails to predict precursor's arrival time. Two different approaches, the mean rate of energy transport and Airy-wave analysis, are proposed for the description of the actual physical process of energy transport by precursors. The influence of the range-dependent bathymetry on a precursor structure is addressed. The presence of precursors appears to be sensitive to range dependence and may be diminished due to rapidly changing bathymetry. Based on numerical results, inversion procedures of extracting different environmental and source parameters from a received pulse structure are discussed.

Analysis of fluid flow and energy transport in Czochralski's process

In this paper the conjugate fluid flow and energy transport problem (involving conduction–convection–radiation heat transfer) resulting from the Czochralski crystal growth process is analysed. The solidifying material is treated as a pure and semitransparent substance with material properties depending neither on temperature nor on the wavelength. The solution of the problem is obtained iteratively using two computer codes: FLUENT, a commercial CFD package, and BEM-based in-house code capable of analysing the radiative heat transfer in the entire computational domain. Obtained results not only show velocity field and temperature distribution within the bodies under consideration but also demonstrate the influence of thermal radiation on these quantities.

Transport in the static diffusion cloud chamber revisited

The static diffusion chamber (SDC) allows the measurement of critical supersaturation and of nucleation rates and it is a powerful instrument for the vapor nucleation study. Earlier, within the scope of the International Nucleation Workshop Group, nucleation rates of the n-pentanol–helium system have been measured using different experimental techniques. Disagreement of experimental data obtained using the static diffusion chamber and data obtained using other methods, particularly the laminar flow diffusion chamber, can be explained by re-examining the mass and energy transport analysis used to describe static diffusion chamber operation. In the present research we describe the mass and energy transport in the SDC modeled as an effectively open system with mass and energy transport in one direction with a nonzero diffusion flux at the system boundaries. Calculated values for vapor supersaturation are compared with the n-pentanol nucleation rate experimental results of the American–Czech group [M. Rudek, J. L. Katz, I. Y. Vidensky et al., J. Chem. Phys. 111, 3623 (1999)] and with a nucleation rate Reference Equation obtained from an earlier investigation involving the n-pentanol–helium system. From our results one can see that there is a significant difference in the calculated supersaturation for all of the data. The magnitude of this difference is quite large even for the relatively small vapor mass fractions at a nucleation temperature of 260 K. We also note that the calculated nucleation temperatures from our analysis are slightly larger than those reported in the work of Rudek et al.4 We performed our calculations with and without the thermal diffusion term. We observed that the effect of thermal diffusion on the transport process is relativelly small and is not particularly essential to include in this comparison that we are making the effects of the different flux boundary conditions.

Silver mass flow in high-voltage fuses

In order to model fuse operation during circuit interruption, a detailed mass and energy transport analysis is needed. In this paper, using a novel method, the mass flow of the fuse element material, silver for this example, is presented. By neutron activation of part of the element, we are able, after interruption, to trace the distribution of the dispersed element material. We show that there is a silver mass coming from the arc ignition zone to the extremities, mainly in the direction of the anode.

Flame structure and burning rate of ammonium perchlorate/hydroxyl-terminated polybutadiene propellant sandwiches

The gas-phase flame structure that forms over a lamina of hydroxyl-terminated polybutadiene (HTPB) binder (50 to 450 μm) sandwiched between layers of ammonium perchlorate (AP) has been investigated through measurements of the surface regression rate of the interface region, ultraviolet emission and transmission imaging of the gas-phase flame zone, and numerical simulations using simplified kinetics. The results show that over the observed pressure range (0.2 to 3.2 MPa), for binder widths from 100 to 450 μm, the regression rate is primarily a function of pressure ( r b ≈p 0.4 ) and is relatively independent of binder width. At binder widths below 100 μm, the regression rate is reduced, presumably due to locally lean conditions created by diffusive mixing. The imaging results suggest the existence of relatively UV-inactive leading-edge flames that form on the AP side of the interfaces adjacent to the surface and probably dominate the regression rate. These leading-edge flames are followed by a relatively UV-active secondary flame region downstream. Both the leading-edge and secondary flames show a tendency to merge into a single flame for thin binder and at lower pressures (low Peclet and Damkohler numbers), and to split into two distinct flames for thick binder ( Pe> 2) and at higher pressures (high Da ). The modeling results show that simplified kinetics representing the AP monopropellant flame and the AP-binder non-premixed flame, in the framework of a species and energy transport analysis, can predict surface heat feedback distributions that correlate reasonably well with observed surface profiles.

Improved confinement and transport studies in the reversed field experiment (RFX)

This paper presents results obtained on the Reversed Field eXperiment, RFX [G. Rostagni, Fusion Engineering and Design 25, 301 (1995)], on the study of local transport properties of the RFP configuration both in the standard regime and during improved confinement phases obtained with poloidal current drive. The plasma core is dominated by magnetic turbulence, as indicated by both energy and particle transport analysis. Diffusivity decreases toward the edge and is reduced in the core at high Lundquist number. The edge region is apparently not affected by dynamo mode turbulence and determines global confinement in standard operation. Particle and heat diffusivity in this region show a favorable dependence with increasing density. The most interesting feature of the edge region of RFX consists of a sheared radial electric field with shearing rate comparable to that observed in tokamaks. Indications of turbulence reduction in the shear layer have been obtained. Enhanced energy confinement has been produced by pulsed poloidal current drive (PPCD). A clear reduction of the dynamo activity has been observed with a decrease of core thermal diffusivity to level comparable to the edge and global confinement improvement up to a factor of 3.

Quench study and helium transport in tightly wound coils

In quench analyses of helium bath cooled superconducting magnets, the helium cooling is often treated as a cooling term that is generally a function of conductor temperatures. Such a method can encounter difficulties when dealing with a tightly wound coil where flow resistance is significant. In this case, helium acts not only as a coolant or thermal mass but also as a medium through which thermal energy is being transferred. The mass and energy transport of helium thus plays an important role in the normal zone propagation/expansion and the magnet overall quench performance. This paper discuss a quench study that incorporates the analysis of helium mass and energy transport with the overall quench thermal analysis. Experiments have verified this approach and showed that its prediction is in good agreement with test results.

Experimental analysis of internal energy transport in the presence of coherent motion

The paper presents the internal energy budget in the initial region of the slightly heated free round jet in the presence of column-mode coherent structures. The budget was obtained by the quantitative evaluation of the shares of particular streams of internal energy transported in the flow-field considered. The input data for calculations have been obtained by the hot-wire measurements of three components of instantaneous velocity and instantaneous temperature. All the terms of the internal energy budget have been determined experimentally except the pressure-velocity term which was treated as a closing quantity. The results of the study suggest, that the internal energy of the flow is determined by the mutual balance of convection realized by the mean, oscillatory and random components of motion accompanied by the work of pressure-velocity correlations. It appears furthermore, that the heat transfer in the initial jet area is realized mainly by random fluctuations of proper turbulence motion, generated, however, in substantial part by coherent structures existing in the flow-field considered.

Liquid crystal visualization of the effects of crucible and crystal rotation on Cz melt flows

Liquid crystals have been used to visualize the temperature field in a simulated Czochralski system. A versatile image processing software has been developed to obtain radial and axial temperature gradients that allow a detailed analysis of momentum and energy transport. The change in the meridional temperature profile with a change in crucible rotation rate is found to be significant. The axial temperature gradient has been found to increase with the rotation rate. Crystal rotation for a low Re s case was studied to emphasize the interaction of buoyancy-driven and rotationally driven forces which makes the flow field susceptible to unstable behavior.

Linear Raman Spectroscopy on Droplet Chains: A New Experimental Method for the Analysis of Fast Transport Processes and Reactions on Microparticles

A new experimental method for the analysis of mass and energy transport and reactions on microparticles is presented. A chain of microdroplets from a vibrating orifice generator was injected into a quiescent gas phase. Linear Raman spectra from the microparticles and the surrounding gas were taken at different distances from the generator. Concentration changes were measured as a function of droplet lifetime. A period of time of up to 20 ms could be studied with a resolution of 10 μs. An argon-ion laser in a 90° scattering geometry was used for excitation. Spectra were taken through a modified double monochromator with a two-dimensional charge-coupled device (CCD) detector, one axis of which was used for spatial resolution. Profiles of gaseous components near the droplets could be measured with a resolution of 50 μm. The method has been applied to analysis of absorption, dissociation, and isomerization in the SO2–H2O system and to the investigation of the desorption process of CO2 from water droplets. Chemical components in gas and liquid phase could be separated. The detection limit in aqueous media was 1 mmol/L.

Thermal venting to recover less-volatile hydrocarbons from the unsaturated zone, 1. Theory

Thermal venting is a remediation technique suitable to the liquid unsaturated zone to enhance recovery of less-volatile residual hydrocarbon contaminants. Thermal venting is different to traditional soil venting because heated air instead of air at ambient conditions is applied to the contaminated zone. The vapor pressure of a less-volatile contaminants is typically increased by temperature causing the gas-phase concentrations to increase by three- to five-fold over a temperature increase of 20–30°C. The work described in this first paper provides the theoretical framework of analysis related to thermal venting. The analysis included nonisothermal gas flow, thermal energy transport and multicomponent mass transport in a multiphase porous medium. The transient gas flow analysis included the effect of temperature on fluid properties and gas compressibility. The heat energy transport analysis was performed under the thermodynamic equilibrium condition with phase-summed effective thermal properties. Multi-component mass transport was performed under local equilibrium for partitioning between phases. Model verification was performed to the extend possible using analytical and available experimental data for different physical processes. The second paper of this two-part series will demonstrate the applicability of thermal venting technique through numerical simulations of hypothetical laboratory and field-scale scenarios.

Global and local energy confinement properties of simple transport coefficients of the Bohm type

Global and local energy transport analysis of experimental results in TFTR and JET indicate that transport models of the Bohm type allow a better representation of experimental data than models of the gyro-Bohm type. Hence a Bohm-like model has been developed by allowing a dependence on a few dimensionless parameters so as to reproduce the main features of global L-mode thermal confinement scaling laws in tokamaks and to obtain bowl-shaped thermal diffusivity profiles. The electron temperature profiles predicted by this model are shown to be in agreement with measured ones in a variety of steady-state and time-dependent JET L-mode discharges.

Computer aided analysis of carrier energy transport in mosfets

The two-dimensional numerical simulation of energy transport for MOSFETs is presented, in which the effect of generation, recombination and temperature gradient of carriers on the characteristics of devices are considered. An improved mobility model is also proposed. The numerical results of micron and submicron MOSFETs show that the present model fits experiment very well.

Analysis of energy and particle transport and density profile peaking in the improved Ohmic confinement regime

The local energy and particle transport and density profile peaking in improved Ohmic confinement (IOC) discharges of ASDEX have been explored by computer simulations. It is shown that the observed improvement of the energy and particle confinement is due to a two to three times reduction of the electron heat diffusivity χe and the diffusion coefficient D that is correlated with the density scale length, while the ion heat diffusivity χi is constant. This result agrees with measurements of the diffusion coefficient and with the coupling between χe and D which was found in all confinement regimes. It is shown that there are lower limits for χe and D. Empirical relations for χe, χi D and the inward drift velocity vin and their scalings in different confinement regimes are presented. The enhancement factor for χi with respect to the neoclassical value is found to be 1.4. Modelling of the measured density profiles requires a time independent ratio vin/D and a feedback controlled decline of the fuelling rate. Simulations with a constant high particle source yield no density profile peaking (saturated Ohmic confinement, SOC). At a given line averaged density, two steady state solutions for the density profile are obtained which correspond to high (SOC) and low (IOC) refuelling rates.

Analysis of Energy and Momentum Transport for Fluid Flow Through a Porous Bed

This paper presents an analysis for the forced convective flow of a gas through a packed bed of spherical solid particles, and the associated heat transport processes. Ergun’s correlation was used as the vapor phase momentum equation in order to account for the inertia effects as well as the viscous effects. No local thermal equilibrium was assumed between the solid and the vapor phases. A thorough discussion of the thermal interactions between the solid and vapor phases and their effects on the fluid flow as well as the pressure and density fields is presented. The analysis shows that the local thermal equilibrium condition was very sensitive to the particle Reynolds number (Rep) and the Darcy number (Da) while thermophysical properties did not have a very significant effect on this condition. On the other hand, two-dimensional behavior of certain variables was found to be very sensitive to thermophysical parameters but insensitive to Rep and Da.

Analysis of finite length dynamics in Czochralski crystal growth

In the analysis of energy transport within crystals grown by the Czochralski process, time dependence appears in both the boundary conditions, through the changing crystal shape, and in the energy equation, by inclusion of the unsteady term. Commonly, these phenomena are neglected by utilization of the quasi-steady state approximation. The present study examines the validity of the approximation with respect to changing crystal length. A one dimensional model, neglecting phenomena occuring at the crystal-melt interface, is developed so that the influence of time dependent changes in crystal length on the dynamics of this process can be evaluated. Finite difference solutions of this relatively simple model are found and used to predict crystal temperature distribution and pull rate. It is shown that use of the quasi-steady state approximation can lead to errors in calculating both the crystal pull rate and the “infinite”, or critical, crystal length. Also, it was found that the choice of initial condition can have a significant effect on early-time crystal growth behavior.