Speed Of Interface Research Articles

A novel technique for measuring the thermal conductivity of metallic materials during melting and solidification

A new technique for measuring the thermal conductivity of metallic materials during liquid/solid phase transformation is proposed and applied to the determination of the thermal diffusivity and thermal conductivity of Wood's metal (Bi, 48%; Pb, 26%; Cd, 13%; Sn, 13%) at the melting point. The technique incorporates measurements in two sequences: (1) during a one-dimensional propagation of the phase transition interface, and (2) during a quasi-equilibrium state where the interface is stationary. The position of the interface is determined from measurement of the electrical resistance over the specimen including the interface. The resistance over time obtained during the melting/freezing processes enables the determination of the speed of the solid-liquid interface. The thermal diffusivity and conductivity at the interface can be evaluated from the speed of the interface, temperature gradients normal to the interface, and thermal properties. The mean value of the thermal conductivity at the transition temperature, was found to be 32.9 Wm-1 degrees C-1 and 22.4 Wm-1 degrees C-1 for the solid and the liquid phases respectively. Independent measurements of the electrical resistance gave the ratio of the resistivity of the solid and the melt equal to 1.51. A Lorenz number is evaluated to be about twice the theoretical value for a metal. A brief discussion of a tentative separation of the electronic and the lattice component of the thermal conductivity is made.

Prediction method for thermal stratification in a reactor vessel

The prediction method for thermal stratification phenomena in a fast breeder reactor is described. The focus of attention is placed on the applicability of water test results to predict thermal stratification phenomena in a real plant. The basic feature of thermal stratification was examined in a cylindrical plenum, using water and sodium as test fluids. The similitude relationship between a small-scale test and a real plant is discussed in order to understand the experimental results. The scale-model experiments for LMFBRs (liquid metal-cooled fast breeder reactors) were also performed to see the effects of a reactor configuration and reactor-trip operation condition. Then the magnitudes of the temperature gradient and the ascending speed of stratified interface in the hot plenum of LMFBRs were predicted, based on the results of the water scale-model.

Effects of Reynolds number and Richardson number on thermal stratification in hot plenum

Thermal transient water tests were performed using a simplified hot plenum model of a pool-type LMFBR to examine the fundamental characteristics of thermal stratification during reactor trips. These tests were divided into two series to clarify the effects of (1) Reynolds number and (2) Richardson number on the behavior of thermal stratification. The results of the first series indicated that the characteristics of thermal stratification were independent of Reynolds number in the range of Re > 10 4. It was concluded from the results of the second series that the rising speed of the thermal interface and the temperature gradient at the interface varied proportionally with Ri −1 2 and Ri 1 2 , respectively. In addition, large scale internal waves, called internal standing waves, were observed under the condition of Re > 10 4 and 1 < Ri < 5.

Factors that influence lymphocyte yields in lymphocytapheresis.

The recent use of lymphocytapheresis to treat immune-mediated diseases such as rheumatoid arthritis prompted a study of factors that influence the cell composition of lymphocytapheresis concentrates. Following single cytapheresis procedures, using protocols recommended by manufacturers, lymphocyte yields were significantly higher with the model 2997 (IBM) and CS-3000 (Fenwal) cell separators as compared to the model 30 (Haemonetics) separator (9.8 +/- 1.1 and 7.1 +/- 1.2 X 10(9) lymphocytes, respectively, versus 4.6 +/- 1.1 X 10(9); p less than 0.01). The lymphocyte concentrate obtained with the CS-3000 separator contained the smallest number of monocytes (0.6 +/- 0.4 X 10(9) versus 1.4 +/- 1.6 and 1 +/- 0.3 X 10(9) for the model 2997 and 30 cell separators, respectively). Platelet contamination of the lymphocyte concentrate was highest with the CS-3000 (6.5 +/- 2.4 X 10(11], and erythrocyte contamination was highest when the model 30 was used (21 +/- 3.0%). Studies using the model 2997 indicated that lymphocyte yields were significantly influenced by donor pre-apheresis absolute lymphocyte counts, and for this cell separator by specific operating variables, such as channel centrifugation speed and positioning of the red cell interface during lymphocyte collection. Maximal yields were obtained when the channel centrifugation speed was 800 to 1000 rpm (equivalent to 100-150 X g) and the red cell interface was adjusted to yield a cell concentrate with a hematocrit less than 4 percent. These results suggest that it will be necessary to standardize lymphocytapheresis collection protocols in future studies to assess the role of lymphocytapheresis in the management of immune-mediated diseases such as rheumatoid arthritis.

Mathematical analysis of segregations in continuously-cast slabs.

A method of mathematically analyzing interdendritic microsegregation was established using finite difference method and taking into consideration the diffusion of the solute in the solid and liquid phases. The cross-sectional shape of dendrites and the fact that the enrichment of the solute in the liquid phase at the solid-liquid interface restrains the advancement speed of the solid-liquid interface were considered. Directional solidification tests to examine interdendritic segregation were made to verify the mathematical analysis method established. The advantages of the new method over other methods were discussed. Then, spot-like segregations were mathematically analyzed applying the same method, and the results were in good agreement with the observations in continuously-cast slabs.

Crystal Growth and Solute Trapping

ABSTRACTA simple model for solute trapping during rapid solidification is presented in terms of a single unknown parameter, the interfacial diffusivity Di. A transition from equilibrium segregation to complete solute trapping occurs over roughly an order of magnitude in growth speed, as the interface speed surpasses the maximum speed with which solute atoms can diffuse across the interface to remain ahead of the growing crystal. This diffusive speed is given by Di/λ, where λ is the interatomic spacing, and is typically of the order 10 meters per second. Comparison is made with experiment. The steady–state speed of a planar interface is predicted by calculating the free energy dissipated by irreversible processes at the interface and equating it to the available driving free energy. A solute drag term and an intrinsic interfacial mobility term are included in the dissipation calculations. Steady–state solutions are presented for Bi–doped Si during pulsed laser annealing.

Axial confinement of plasma by a magnetic trap

The axial confinement of plasma by means of a magnetic trap has been studied in a coaxial electromagnetic shock tube. The propagation speed of the magnetic trap vacuum field-plasma interface, as it expanded into the plasma, was measured by magnetic field probes. The subsequent density change in the trapped plasma was determined by a Michelson He–Ne laser interferometer. Definite plasma trapping was achieved.

The starting problem for spherical elastic-plastic waves of small amplitude

The character of the wave motion produced in an elastic-plastic body of infinite extent by the application of a uniform pressure p (t) to the surface of a spherical cavity is known to depend upon the magnitude of p(0) in relation to the critical pressure p cr = Y(0) (1 − v)/(1 − 2 v), where Y (0) is the initial yield stress and v the Poisson's ratio of the material. Supposing the deformation to be universally small, we consider in this paper the initial behaviour of stress pulses generated by loading histories for which p(0) ⩾ p cr . The analysis is based upon linearized equations for spherically symmetric wave fields in elastic-plastic work-hardening materials given recently by L.W. M orland, and the formulation of the basic equations is so arranged as to exhibit clearly the distinction between the cases of critical and supercritical loading ( p(0) = p cr and p(0) > p cr , respectively). For critical loading a criterion for the spread of plastic deformation away from the cavity wall is obtained together with a formula giving the initial speed of the elastic-plastic interface Σ p in terms of the initial loading rate p' (0). A similar growth criterion is found for supercritical loading and it is proved that in this case Σ p initially propagates as a plastic shock wave with constant speed. The resulting simplification of the basic equations makes possible an analytic solution which is discussed in some detail. In particular, it is shown that the starting solution breaks down after a finite time t ∗ due to the vanishing of the discontinuities on Σ p. Validity is maintained throughout the interval [0, t ∗] only if the rate of plastic working nowhere falls to zero and a numerical investigation confirms that this condition is satisfied in the special case of supercritical step loading of an elastic-perfectly plastic material. Results illustrating the nature of the stress pulse in this particular situation are presented graphically.

Theoretical penetration of hypervelocity projectiles into massive targets

A model of the penetration of a hypervelocity projectile into a massive target is formulated, and a quasi-theoretical technique for predicting the penetration is developed. It is assumed that 1) the projectile is significantly deformed immediately after impact by the initial shock wave and subsequent expansion waves, and 2) after the initial impact, the deformed projectile is retarded by a pressure on its face resulting from weak waves. The equation of projectile motion is integrated to obtain the depth of penetration. The resulting theoretical penetration is shown to be in agreement with experimental data. Nomenclature C = weak plastic wave speed, constant c = weak plastic wave speed, variable (c) == average wave speed D = projectile diameter K = penetration coefficient L = projectile length p = pressure on projectile-target interface P = penetration depth from face of target S = shock constant t = time after impact u = speed of projectile-target interface U = shock speed v = speed of projectile center of mass V = impact speed Vf = (<rvt/KPtCt)[l+(ptCt/pPCp)] w = material speed x = depth of projectile-target interface z — depth from target surface p — density a — material strength