The persistence of Maxwellian D and T distributions during burn in inertial confinement fusion

We present particle simulations of the heating of a DT plasma by fusion-produced α-particles. The D, T and α-particles are each treated as separate kinetic species while the electrons are assumed to be Maxwellian. Fusion reactions are also simulated for the D and T ions in such a way as to account correctly for any non-thermal effects. It is shown that the D and T ions remain close to Maxwellian under a wide range of conditions and correspondingly the fusion reactivity remains thermal.     

Bayesian inference of inaccuracies in radiation transport physics from inertial confinement fusion experiments

First principles microphysics models are essential to the design and analysis of high energy density physics experiments. Using experimental data to investigate the underlying physics is also essential, particularly when simulations and experiments are not consistent with each other. This is a difficult task, due to the large number of physical models that play a role, and due to the complex and noisy nature of the experiments. This results in a large number of parameters that make any inference a daunting task; it is also very important to consistently treat both experimental and prior understanding of the problem. In this paper we present a Bayesian method that includes both these effects, and allows the inference of a set of modifiers that have been constructed to give information about microphysics models from experimental data. We pay particular attention to radiation transport models. The inference takes into account a large set of experimental parameters and an estimate of the prior knowledge through a modified χ² function, which is minimised using an efficient genetic algorithm. Both factors play an essential role in our analysis. We find that although there is evidence of inaccuracies in off-line calculations of X-ray drive intensity and Ge L shell absorption, modifications to radiation transport are unable to reconcile differences between 1D HYDRA simulations and the experiment.     

Laser absorption density direct measurements with limitation of temperature variation field in shock-induced gaseous mixing

We describe a laser absorption technique to obtain reasonably accurate density profiles within a shock-induced Richtmyer-Meshkov mixing zone. Assuming a small temperature variation through the probed region, a single wavelength absorption experiment only is needed. When this criterium is satisfied, the technique described represents a considerable simplification over the more generally required dual wavelength experiments. Received 4 May 1996 / Accepted 7 October 1996     

Aspect ratio effect on natural convection in water near its density maximum temperature

The effect of the aspect ratio on natural convection in water subjected to density inversion has been investigated in this study. Numerical simulations of the two-dimensional, steady state, incompressible flow in a rectangular enclosure with a variety of aspect ratios, ranging from 0.125 to 100, have been accomplished using a finite element model. Computations cover Rayleigh numbers from 10³ to 10⁶. Results reveal that the aspect ratio, A, the Rayleigh number, Ra, and the density distribution parameter, R, are the key parameters to determine the heat transfer and fluid flow characteristics for density inversion fluids in an enclosure. A new correlation for predicting the maximum mean Nusselt number is proposed in the form of , with the constants a and b depending on density distribution number R. It is demonstrated that the aspect ratio has a strong impact on flow patterns and temperature distributions in rectangular enclosures. The stream function ratio Ψ_inv/|Ψ_reg| is introduced to describe quantitatively the interaction between inversional and regular convection. For R=0.33, the density inversion enhancement is observed in the regime near A=3.     

Error estimates for Rayleigh scattering density and temperature measurements in premixed flames

Rayleigh scattering has become an accepted technique for the determination of total number density during the combustion process. The interpretation of the ratio of total Rayleigh scattering signal as a ratio of densities or temperatures is hampered by the changing composition through a flame, since the average Rayleigh scattering cross-section depends on the gas composition. Typical correction factors as a function of degree of reaction, fuel and equivalence ratio were calculated. The fuels considered were H₂, CH₄, C₂H₄, C₂H₆ and C₃H₈. Factors as low as 0.7 and 0.56 were found for the heaviest hydrocarbon fuel at large equivalence ratio for interpreting the Rayleigh scattering intensity as gas density and inverse temperature, respectively. This is primarily due to the presence of CO and H₂ as intermediates. As CO and H₂ are subsequently oxidized to CO₂ and H₂O, these factors approach 1.0. Conversely, the worst case, when using H₂ as a fuel, occurs in the post flame zone. However, the correction factors for H₂ are near 1.0 and the errors involved will, in general, remain within the expected experimental accuracy of a typical Rayleigh scattering system. Linear correlations of correction factors with equivalene ratio and with the product of equivalence ratio and fuel molecular weight were found and presented. The interpretation of Rayleigh scattering as temperature was found to have larger errors than the interpretation as density. Corrections for changes in gas composition were applied to Rayleigh scattering temperature measurements in the post flame region of CH₄ and C₃H₈ flames with equivalence ratios of 0.75 and 1.0. The corrected temperatures were in excellent agreement with thermocouple measurements.List of symbols A ₁, A ₂ correlation coefficients - B ₁, B ₂ correlation coefficients - C ₁, C ₂ correlation coefficients - D ₁, D ₂ correlation coefficients - C calibration constant for Rayleigh scattering optics - H total enthalpy - Î I _R /I _RO - I _i incident laser intensity - I _R Rayleigh scattering intensity - I _R0 Rayleigh scattering intensity at reference condition - N total number density of gas - N ₀ total number density of gas at reference condition - n _i index of refraction of species i - – T/T _O - T temperature - T _a adiabatic flame temperature - T ₀ reference temperature - t time - W/W ₀ - W mean molecular weight - W ₀ mean molecular weight at reference condition - W _ij rate of production of species i by reaction j - X _i mole fraction of species i - degree of reaction (T – T ₀)/(T _a – T ₀) - laser wavelength - ₀ Loschmidt number - /₀ - density - ₀ density at reference condition - dimensionless mean Rayleigh scattering cross-section - _Ri Rayleigh scattering cross-section of species i - scattering angle measured from the electromagnetic field vector - equivalence ratio     

Limitations of temperature measurements with holographic interferometry in the presence of pressure variations

In recent years oscillatory flows have shown to be a promising strategy to enhance heat transfer. However, the mechanisms underlying oscillatory heat transfer enhancement are not yet completely understood. One problem, when investigating heat transfer in oscillatory flows experimentally, is to resolve the temperature distribution as a function of time. This is one reason that most studies reported in the literature so far were restricted to frequencies of a few hertz. As shown in this paper, an appropriate tool to investigate oscillatory heat transfer phenomena at higher frequencies (1000 Hz) is real time holographic interferometry (HI) combined with high-speed cinematography. In the present paper HI was applied to study acoustically driven flow. To apply HI to such a physical situation it was necessary to expand its applicability to cases where changes in the refractive index are caused not only by temperature changes but also by pressure variations. For this purpose a new evaluation formula that accounts for pressure variations was derived. On the example of the acoustic field, we discuss the impact of the pressure variations on temperature measurements. Additionally, an image processing algorithm was developed that allows the measurement of time dependent temperature distributions. The uncertainties of the temperature measurements introduced by the image processing algorithm were found to be in the range of thermocouple measurements.     

Emissivity and temperature measurements under shock loading,along the melting curve of bismuth

Measuring shock-induced temperatures in metals is a difficult task. We have developed a new device to measure emissivity of shock-loaded metals in contact with a lithium-fluoride anvil. This diagnostic, associated with standard pyrometry, allows to improve the accuracy on temperature. We have performed a series of experiments, including a few ones with this new diagnostic, to complement study of bismuth. Experimental temperatures and emissivities appear to be in good agreement with those predicted by theory.Received: 22 April 2002, Accepted: 10 February 2003, Published online: 20 May 2003D. Partouche-Sebban: dmps@lanl.gov     

Thomson scattering in dense plasmas with density and temperature gradients

Collective X-ray Thomson scattering has become a versatile tool for the diagnostics of dense plasmas. Assuming homogeneous density and temperature throughout the target sample, these parameters can be determined directly from the plasmon dispersion and the ratio of plasmon amplitudes via detailed balance. In inhomogeneous media, the scattering signal is an average of the density and temperature dependent scattering cross-section weighted with the density and temperature profiles. We analyse Thomson scattering spectra in the XUV range from near solid density hydrogen targets generated by free electron laser radiation. The influence of plasma inhomogeneities on the scattering spectrum is investigated by comparing density and temperature averaged scattering signals to calculations assuming homogeneous targets. We find discrepancies larger than 10% between the mean electron density and the effective density as well as between the mean temperature and the effective temperature.     

3-D analysis of temperature distribution in the material during pulsed laser and material interaction

Recently, lasers are being increasingly used in the industry owing to their precision and low cost. Material is heated and evaporated during laser and material interaction due to the absorption of laser beams by the material. In this study, a 3-D Laser heating model including evaporation has been solved using the electron- kinetic theory approach. The basis in examining the problem using the kinetic theory approach is to describe the heat conduction through electron-phonon and molecule-phonon collisions. The problem is solved by using the electron-kinetic theory approach in such a way that heat conduction is taken into account until the material is heated to its melting temperature and non-conduction limited heat transfer is considered after the melting temperature is reached. Non-conduction limited heat transfer through the phase change process is resulted from vacancy-molecule collisions. A numerical scheme is introduced to solve the governing equation, owing to the fact that the energy equation resulted is in the form of integro-differential equation. Four different materials, namely iron, nickel, tantalum and titanium are chosen in this study determine the material response to laser pulse heating. For each material, time dependent temperature distribution through the depth of the material and on the surface of the material is computed and analyzed for four different materials.     

Flow structure and wall layer control in a lower half heated upper half cooled enclosure with superimposed temperature deviations

This paper presents an investigation on the effects of superimposed temperature deviations as a control technique for the flows and mixing in lower half heated upper half cooled enclosures. Results show that the strength of the wall layer depends on the difference between the wall surface temperature and the fluid core temperature. The location of the head-on collision between a pair of upward/downward wall layers, which controls the mixing and fluid exchange between the two halves, is determined by the wall layer flow momentum strengths. Elevating/reducing the wall temperature by a superimposed temperature deviation is an effective control for the flow and mixing in such enclosures. Heat transfer analysis shows that the superimposed temperature deviations have minor effects on the total heat flow rate from the lower walls. Thus, this technique can be applied onto reactor vessels without modifying the reactor vessel configuration.     

Estimation of radiative properties and temperature distributions in coal-fired boiler furnaces by a portable image processing system

This paper presented an experimental investigation on the estimation of radiative properties and temperature distributions in a 670 t/h coal-fired boiler furnace by a portable imaging processing system. The portable system has been calibrated by a blackbody furnace. Flame temperatures and emissivities were measured by the portable system and equivalent blackbody temperatures were deduced. Comparing the equivalent blackbody temperatures measured by the portable system and the infrared pyrometer, the relative difference is less than 4%. The reconstructed pseudo-instantaneous 2-D temperature distributions in two cross-sections can disclose the combustion status inside the furnace. The measured radiative properties of particles in the furnace proved there is significant scattering in coal-fired boiler furnaces and it can provide useful information for the calculation of radiative heat transfer and numerical simulation of combustion in coal-fired boiler furnaces. The preliminary experimental results show this technology will be helpful for the combustion diagnosis in coal-fired boiler furnaces.     

The effect of roller pressure and share of plant matter in mulching soil cultivation on its density and water content

The aim of this study was to assess the impact of the roller load (with cultivating tools) and doses of plant matter (straw and charlock) mixed with soil on the air and humidity conditions of such soil. The innovation of the research consisted in abandoning the use of Kopecky’s cylinders: the bulk density of mulched soil was determined by measuring its mass and volume, which it obtained in vases before and after the roller work. Capillary infiltration was also carried out for soil in vases.Variable research factors characterizing the roller working conditions in the mulching tillage, were: source/type of plant material cut into 10 cm chopped straw, its share in soil, three ranges of soil water content and vertical unit load on the roller.Increasing the straw dose to 30 Mg^.ha⁻¹ reduces the bulk density from 1.17 to 0.76 g^.cm⁻³, while increasing the dose of charlock to 60 Mg^.ha⁻¹ under these conditions, it reduces the density to 1.03 g^.cm⁻³. At the same time, humidity conditions change: volumetric water content decreases in case of straw from 13.9% to 8.5% and increases in case of charlock to 17.4%. Changes occur also in case of full water capacity.     

A physically based model of temperature and strain rate dependent yield in BCC metals: Implementation into crystal plasticity

In this work, we develop a crystal plasticity finite element model (CP-FEM) that constitutively captures the temperature and strain rate dependent flow stresses in pure BCC refractory metals. This model is based on the kink-pair theory developed by Seeger (1981) and is calibrated to available data from single crystal experiments to produce accurate and convenient constitutive laws that are implemented into a BCC crystal plasticity model. The model is then used to predict temperature and strain rate dependent yield stresses of single and polycrystal BCC refractory metals (molybdenum, tantalum, tungsten and niobium) and compared with existing experimental data. To connect to larger length scales, classical continuum-scale constitutive models are fit to the CP-FEM predictions of polycrystal yield stresses. The results produced by this model, based on kink-pair theory and with origins in dislocation mechanics, show excellent agreement with the Mechanical Threshold Stress (MTS) model for temperature and strain-rate dependent flow. This framework provides a method to bridge multiple length scales in modeling the deformation of BCC metals.     

The experimental investigation of heat transport and water infiltration in granular packed bed due to supplied hot water from the top: Influence of supplied water flux, particle sizes and supplied water temperature

In the present study an experimental investigation of heat transport and water infiltration in granular packed bed (unsaturated porous media) due to supplied water flux is carried out. The study is focus on the one-dimensional flow in a vertical granular packed bed column assuming local thermal equilibrium between water and particles at any specific space. This experimental study described the dynamics of heat transport and water infiltration in various testing condition. Experimentally, the influences of particle sizes, supplied water flux and supplied water temperature on heat transport and water infiltration during unsaturated flow are clarified in details. The results showed that the granular packed bed with larger particle size results in faster infiltration rate and form a wider infiltration depth. Furthermore, the increase of the supplied water flux and supplied water temperature corresponds to faster infiltration rate, but the results not linearly related to the interference between the heat transport and hydrodynamics characteristics in granular packed bed.     

Wavy texture in pressure-driven startup flows of liquid crystalline polymer solutions through a slit cell: effects of polymer concentration and solution temperature

Dependences of wavy texture on polymer concentration and solution temperature were examined using aqueous solutions of hydroxypropylcellulose (HPC). The phase of aqueous solution of HPC varied from an isotropic (I) system to a liquid crystalline (LC) one through a biphasic (I+LC, LC+I) system with increasing the HPC concentration and/or decreasing the solution temperature. The wavy texture emerged not only in the LC system but also in the LC+I system. Furthermore, induction time of wavy texture was evaluated in terms of apparent shear strain. It is suggested that polydomain structures included in liquid crystalline systems and droplets of isotropic phase in biphasic systems affect the initial stage of emergence of wavy texture at low shear rates.     

Stability of the equilibrium state in a convection model with nonlinear temperature and pressure dependences of density

The convection of a heat-conducting viscous liquid is considered. It is assumed that the liquid density depends quadratically on the temperature and pressure. The instability of the equilibrium state of a free-boundary horizontal layer with respect to small perturbations is studied using a linearization method. It is found that the state of mechanical equilibrium is unstable. Neutral curves are constructed and the critical Rayleigh numbers are found. The results are compared with the well-known solution of the same problem for the limiting case where the density is a quadratic function of temperature and does not depend on pressure. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 66–74, March–April, 2007.     

Grain size,strain rate,and temperature dependence of flow stress in ultra-fine grained and nanocrystalline Cu and Al: Synthesis,experiment, and constitutive modeling

For the first time, high quality bulk nanocrystalline (nc) fcc metals, with least amounts of imperfections, exhibiting high strength and ductility at room and different temperatures, under quasi-static and dynamic types of loading, were prepared and a comprehensive study on their post-yield mechanical properties was performed. This investigation included study of the effect of temperature on stress–strain responses of mechanically milled bulk nc Cu and Al. The samples after preparation through mechanical milling and consolidation processes were subjected to uniaxial compressive loading at quasi-static and dynamic strain rates of 10⁻² s⁻¹ and 1840–3105 s⁻¹, respectively, at temperatures ranging from 223 to 523 K. In both materials strong dependency of flow stress to temperature was observed; this dependency was rather more pronounced when the materials were tested at the quasi-static strain rate. Further, a new grain size and temperature dependent viscoplastic phenomenological constitutive equation, Khan–Liang–Farrokh (KLF) model was developed based on the Khan–Huang–Liang (KHL) constitutive equation. The model was featured to correlate different characteristic behaviors of polycrystalline materials in the plastic regime, as the result of grain refinement. In addition, the viscoplastic responses of bulk Cu and Al of different grain sizes (from sub-micron to nanometer range), and those from bulk nc Cu and Al at different strain rates (quasi-static to dynamic), recently published (21 and 22), were simulated using the newly developed equation. The results confirmed reasonable capability of the developed model to correlate a wide spectrum of the viscoplastic responses of these fcc metals.     

Extrapolation-to-flight of aerodynamic heating measurements and determination of in-flight radiation-equilibrium surface temperature in hypersonic/high enthalpy flow conditions

The previously demonstrated success of the reference enthalpy concept in heat transfer prediction at hypersonic flow conditions is utilized herein to propose a cost-effective methodology for extrapolation-to-flight of Stanton number measurements (or baseline computational results), and the determination of radiation-equilibrium surface temperatures that develop on actual vehicle surfaces during hypersonic/high enthalpy flight conditions. The methodology couples the (analytical) generalized reference enthalpy solution with Euler computations (providing input data along the edge of thin boundary layers) and is, therefore, significantly cheaper and more efficient than the execution of full Navier–Stokes computations that are presently incorporated, particularly so in the thermo-chemically active high enthalpy flow regime. The validity of the proposed methodology is demonstrated in a first step by means of two-dimensional test cases, whereby extrapolated data accuracy is better than 20%.

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Using the gradients of temperature and internal parameters in Continuum ThermodynamicsIntroduction des gradients de température et de paramètres internes en Thermodynamique des Milieux Continus

In this paper, the possibility of using the gradients of the temperature and of the internal parameters as additional state variables in Continuum Thermodynamics is considered. The expressions of the two principles are discussed and Clausius–Duhem inequality is derived under an appropriate statement of the internal entropy production. Several formulations are proposed and compared to existing results in the literature. To cite this article: P. Ireman, Q.S. Nguyen, C. R. Mecanique 332 (2004).