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Heatline approach has been implemented to visualize heat transfer and to study efficient thermal mixing of laminar natural convective flow in a square cavity with distributed heat sources. Four different cases, depending upon the location of the heat sources on the walls of the cavity, are studied. Wide range of fluids ( Pr = 0.015 – 1000 ) have been studied over a range of Rayleigh numbers ( Ra = 10 3 – 10 5 ) . Governing equations and Poisson-type of equations for streamfunction and heatfunction have been solved using penalty finite element method. Heatlines and streamlines are found to be adequate to visualize and understand heat energy distribution and thermal mixing occurring inside a cavity. Various qualitative and quantitative features on variations of local and average Nusselt numbers for test cases are adequately explained based on heatlines. The efficacy of distributed heating over conventional bottom heating for optimal thermal mixing is established via correlating with heatlines and cup-mixing temperature. The distributed heat sources are found to play major role for processing of molten materials and gaseous substances. Overall, it is shown that heatlines give suitable guidelines to assemble discrete heat sources and the heatline analysis on heat flow management with distributed heat sources is reported for the first time in this work.

In the case of a hypothetical severe accident in a Pressurized Water Reactor (PWR), Silver-Indium-Cadmium (SIC) control rod failure occurs early during the sequence. Release of absorber melt could induce early fuel rod degradation by interaction of molten SIC alloy with fuel rod cladding, and the absorber materials could interact with the fission products, affecting significantly their speciation and transport in the primary circuit as well as their behaviour in the containment. This paper summarises the experimental and modelling progress made on this topic within SARNET over the whole project. Following a review of the status of knowledge, including the modelling in the main severe accident codes (ATHLET-CD, MAAP4, SCDAP, MELCOR, ASTEC), detailed calculations of the specific EMAIC and integral PHEBUS FPT2 experiments were performed. Accurate calculation of vapour pressure of the molten absorber elements is needed, requiring reliable values of the activity coefficients. The importance of accurate reproduction of the control rod degradation was shown, with the behaviour of absorber elements at rupture being critical as well as the thermodynamic data and speciation of the system Ag-In-Cd-Zr-H-O. The QUENCH-13 bundle experiment (FZK), conducted with a realistic integral geometry composed of 20 electrical heated rod simulators and one central SIC absorber rod, has helped to characterize the behaviour of absorber elements at the time of rod rupture, with measurements of the SIC release, using impactors (AEKI) and electrical low-pressure impactor and Berner low-pressure impactors (PSI). Coordinated pre and post-test calculations using SCDAP/RELAP5 based codes (PSI), MAAP4 (EDF), ATHLET-CD (GRS), ASTEC (IRSN) helped in defining the test and in its interpretation. Before this experiment, five tests were performed on small-scale SIC control rod samples using different designs and conditions. They helped in defining the conditions for the QUENCH-13 experiment. Five additional tests on similar small-scale samples are foreseen to help interpretation of the QUENCH-13 results. In QUENCH-13 the on-line aerosol measurements with electrical low-pressure impactors indicated control rod failure in the range 1550-1600 K; the test was terminated later at 1813 K by water reflood. Analysis of aerosols measured at sample points in the off-gas line showed significant Cd and In transport after rod failure with a smaller amount of transported Ag. Relocated SIC melt in the form of rivulets was detected in the lower part of the bundle. Investigation of SIC material properties (solidus, liquidus) by further analysis of data from QUENCH-13 is also presented. In parallel, an exhaustive review of activity coefficients of the elements in the SIC melt, including the effect of Zr was began (IRSN with the CNRS Marseille). © 2009 Elsevier Ltd. All rights reserved.

An analysis of the solidification rates of binary mixture melts flowing as a thin film on a cold surface, useful in the separation or purification of eutectic mixtures, is presented. The analysis which incorporates the hydrodynamics of the falling film and the convective heat transfer at the melt/crystal interface was used to determine the average crystallization velocity. The effect of parameters such as Stefan number (subcooling), initial superheat and the melt loading rate on the average crystallization velocity was examined. Experiments were performed using three different binary organic mixtures at subeutectic compositions. The results of the theoretical and experimental studies showed good agreement validating the model. ? 1999 OPA (Overseas Publishers Association) N.V.

In the present study, the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process has been simulated using ABAQUS code finite element software. The temperature dependency of material properties and the expanding of plasma channel radius with time have been employed in the simulation stage. The profile of temperature distribution has been utilized to calculate the dimensions of discharge crater. Based on the results of FEM and the experimental observations, a numerical analysis has been developed assessing the contribution of input-parameters on the efficiency of plasma channel in removing the molten material from molten puddles on the surfaces of workpiece and tool at the end of each discharge. The results show that the increase in the pulse current and pulse on-time have converse effects on the plasma flushing efficiency, as it increases by the prior one and decreases by the latter one. Later, the introduced formulas for plasma flushing efficiency based on regression model were utilized to predict the cardinal parameter of recast layer thickness on the electrodes which demands expensive empirical tests to be obtained. © 2012 Elsevier Ltd. All rights reserved.

Laser micro-polishing (LμP) is a new laser-based microfabrication technology for improving surface quality during a finishing operation and for producing parts and surfaces with near-optical surface quality. The LμP process uses low power laser energy to melt a thin layer of material on the previously machined surface. The polishing effect is achieved as the molten material in the laser-material interaction zone flows from the elevated regions to the local minimum due to surface tension. This flow of molten material then forms a thin ultra-smooth layer on the top surface. The LμP is a complex thermo-dynamic process where the melting, flow and redistribution of molten material is significantly influenced by a variety of process parameters related to the laser, the travel motions and the material. The goal of this study is to analyze the impact of initial surface parameters on the final surface quality. Ball-end micromilling was used for preparing initial surface of samples from H13 tool steel that were polished using a Q-switched Nd:YAG laser. The height and width of micromilled scallops (waviness) were identified as dominant parameter affecting the quality of the LμPed surface. By adjusting process parameters, the Ra value of a surface, having a waviness period of 33 μm and a peak-to-valley value of 5.9 μm, was reduced from 499 nm to 301 nm, improving the final surface quality by 39.7%., SPIE MOEMS-MEMS, January 24-26, 2012, San Francisco, CA, USA, Series: Proceedings of SPIE

The main advantage of ultrashort laser pulses in manufacturing technology is their very high removal rate of material and high quality of microstructures with the smallest dimensions at 1 μm level. The accuracy is mainly due to an almost absence of thermal diffusion into bulk material. In this paper we report the investigation on polycrystalline Cu sample surface treated by 6.7 ps laser pulses with 1030 nm laser light wavelength. Scanning electron microscopy micrographs reveal the presence of jet-like structures with spherical drop-like endings, solidified spheres and many bubble bursts at even lower fluence than the threshold value for the ablation is. Within the molten material the jet-like features are due to an explosion of bubbles originated in solid-liquid-vapor transitions. In the case of below-threshold irradiation, the same objects can be seen along surface scratches, dot contaminations etc., which indicate an increase of the laser light absorption on these inhomogeneities. © 2011 WIT Press.

The deposition of porous La1-xSrx MnO3 (LSM) perovskite cathode materials by conventional plasma spray has been a challenge because of the decomposition of perovskite materials to their suboxides at high temperature. In this paper, the solution precursor plasma spraying (SPPS) process, in which solution precursors of the desired resultant materials are fed into a direct current plasma jet by atomizing gas, was used to simultaneously synthesize LSM perovskite and deposit porous cathode coatings. The experimental results show that process parameters have a significant effect on the fabricated coatings. The perovskite coatings consist of porous agglomerates of small particles with rounded features and local denser regions referred to as thick flakes. The small particles and thick flakes were held together by the previously molten material. There are two kinds of pores in the fabricated coatings: large pores located between the agglomerates and fine pores inside the agglomerates. The porous LSM cathode coatings have 20-40 area % of desirable homogeneous pores determined by several processing parameters. X-ray diffraction of sintered coatings shows that no suboxides of La 1-xSrx MnO3 perovskite appear. The results of this project indicate that the SPPS is a potential process to produce high quality cathodes for solid oxide fuel cell application. © 2011 American Society of Mechanical Engineers.

Uniform temperature distribution is a key parameter in many thermal processing applications. A considerable amount of additional energy is used to enhance the fluid mixing in order to maintain the temperature uniformity, but that affects the overall efficiency of the process. In this article, an alternate approach is proposed for maintaining uniform temperature via various distributed/discrete heating strategies while maintaining the minimal entropy generation. The system of laminar natural convection in differentially and discretely heated square cavities filled with various materials (molten metals, air, aqueous solutions, oils) is considered, and finite element simulations are performed for a range of Rayleigh numbers (Ra=103-105). Entropy generation is evaluated using finite-element basis sets for the first time in this work, and the derivatives at particular nodes are estimated based on the functions within adjacent elements. Analysis of entropy generation in each case is carried out and a detailed investigation of entropy production due to local heat transfer and fluid friction irreversibilities is presented. It is found that a high thermal mixing may not be the optimal situation for achieving uniform temperature distribution based on entropy production. A greater degree of temperature uniformity with moderate thermal mixing may correspond to minimum entropy generation with distributed heating. Further, based on entropy generation minimization approach, it has been thermodynamically established that the distributed heating methodology with multiple heat sources may be the energy efficient strategy for attaining adequate uniform temperature distribution with minimum entropy generation. Copyright � Taylor & Francis Group, LLC.

Boron carbide is used in many nuclear power plants like BWR, VVER, some PWR, and EPR as a neutron absorber material. Consequently, it is important to assess its role in the core degradation phenomena during a severe accident (SA), as well as that of the carbon gas released from its degradation on the fission products behaviour. This paper describes the progresses achieved in the frame of the Network of Excellence SARNET concerning the B4C control rod degradation modelling in Severe Accident codes, such as ATHLET-CD, ICARE2, ASTEC MELCOR and MAAP. These new developments complete improvements made during the European Union 5th Framework COLOSS project. Starting from basic modelling derived from available tests reported in the literature, large improvements of the kinetic correlation for B4C oxidation were obtained from analytical experiments performed at FzK (Germany) and IRSN (France), mostly in the temperature range above 1400 K. The new modelling was considered in the analysis of experiments involving a B4C control rod in small fuel rod assemblies, such as Phebus FPT3 in-pile experiment, as well as out of pile experiments Quench 07 and 09, aimed at studying the course of severe accidents. Regarding the hydrogen generation, the results given by different code simulations are consistent with the experimental values. Concerning the control rod degradation, SA codes such as ICARE2 and ATHLET-CD, using suitable modelling of B4C oxidation, predicted rather well the total carbon release. The results of the MELCOR code, involving initially a B4C oxidation model designed to be used for BWR control blades, have been largely improved in the most recently released version, with a model extended for PWR B4C control rods. Codes still have some difficulties to reproduce the final degradation of fuel bundles involving B4C rods. Spreading of molten materials from the control rods onto fuel rods of the bundle is suspected, suggesting that the main effect of the B4C control rod materials on the bundle behaviour during degradation is connected with B4C-Stainless Steel (SS) eutectics formation and B4C-SS-Zry liquid mixture relocation. These phenomena are not accounted for in the SA codes. The need for further code developments of the early phase of core degradation is recognized, involving the absorber rod material behaviour. The BECARRE experiments, on-going in the framework of the International Source Term Program, are designed to provide in-depth understanding of these phenomena and help improving their modelling. © 2009 Elsevier Ltd. All rights reserved.

We present an experimental study of the drilling of metal targets with ultrashort laser pulses with pulse durations from 800 fs to 19 ps at repetition rates up to 1 MHz, average powers up to 70 Watts, using an Ytterbium-doped fiber CPA system. Particle shielding and heat accumulation have been found to influence the drilling efficiency at high repetition rates. Particle shielding causes an increase in the number of pulses for breakthrough. It occurs at a few hundred kHz, depending on the pulse energy and duration. The heat accumulation effect is noticed at higher repetition rates. Although it overbalances the particle shielding thus making the drilling process faster, heat accumulation is responsible for the formation of a large amount of molten material that limits the hole quality. The variations of the pulse duration reveal that heat accumulation starts at higher repetition rates for shorter pulse lengths. This is in agreement with the observed higher ablation efficiency with shorter pulse duration. Thus, the shorter pulses might be advantageous if highest precision and processing speed is required.

The fission product (FP) behaviour in PHEBUS FPT0 (fresh fuel rods) and FPT1 (irradiated fuel) in-pile experiments is interpreted. The main experimental results in FPT0 and FPT1 are first summarized, and the FP release rates measured in both tests are reported and related to degradation events. The interpretation is performed in two steps. First, using general knowledge from the open literature and from previous interpretations of VERCORS analytical experiments, a qualitative description of the possible behaviour of fission gases, Cs, Mo and Ba is given by considering only intact fuel geometry. This interpretation is illustrated by calculations performed with the mechanistic MFPR code. Then, in a second step, possible effects of fuel dissolution, foaming and interactions with structural materials are considered. For FPT1, most of the FP release might be explained by mechanisms acting in intact geometry. On the contrary, for FPT0, it is necessary to consider the fuel dissolution by molten non-oxidised Zr, mainly at grain boundaries to explain the early and large FPs release observed in this test. In addition, it is shown that in both tests, the release from the corium molten pool is not significant and that interactions with Zr and Fe from structural materials can strongly reduce the Ba release. © 2005 Elsevier B.V. All rights reserved.

Al-4Cu-xTiB 2 (x = 2.5, 5, 7.5 and 10 wt.%) in situ composites have been successfully prepared by the reaction of mixture of K2 TiF6 and KBF4 with molten alloy. A reaction temperature of 800 �C and a reaction time of 60 min were adopted. A continuous increase in the yield strength and ultimate tensile strength without any significant loss in ductility has been observed with increase in the amount of TiB2 in both as-cast and peak-aged conditions. TiB2 particles enhance the aging kinetics and the time to peak aging at the aging temperature of 170 �C comes down from 40 to 6 h when the TiB2 amount is increased from 0 to 10%. ? 2004 Elsevier B.V. All rights reserved.

International audience; Three series of isotactic polypropylene characterized by different molecular weights and the same isotactic index have been studied during crystallization under static and shearing conditions. The shear is induced by the displacement of a glass fiber in the molten polymer. The monoclinic α-phase is here formed under shear with a columnar organization at the surface of the glass fiber, and does not appear under static condition. The growth-rate, constant during the shear-induced crystallization experiment, is compared with the result obtained from static crystallization. An important increase of the growth-rate due to the shear flow is observed. This increase depends on the molecular structure. The average molecular weights M̄w and M̄z seem to be the most important molecular parameters, for which an excellent correlation is obtained. The increase of these parameters M̄w and M̄z leads to a significant enhancement of the growth-rate, which can be multiplied by a factor of 10 in the present conditions.

Glassy samples with composition (mole %) 50 AgI-33.33 Ag 2 O-16.67V 2 O 5 were prepared by rapid quenching from the melt and characterized by X-ray diffraction and differential scanning calorimetry techniques. The glass transition temperature was observed at 343 K. Conductivity of the glassy sample was found to be 2.3 × 10 −3 ohm −1 cm −1 at 300 K. The diffusion coefficient at 300 K, estimated by microtome sectioning technique with Ag 110m isotope and self absorption technique with Ag 111 isotope was found to be 1.1 × 10 −8 cm 2 /s and 8.9 × 10 −9 cm 2 /s respectively. The estimated diffusion coefficient was compared with the diffusion coefficient evaluated from the conductivity data using Nernst-Einstein relation.

Qualitative and quantitative determination of the release of low-volatile fission products and core materials from molten oxidic corium was investigated in the EVAN project under the auspices of ISTC. The experiments carried out in a cold crucible with induction heating and RASPLAV test facility are described. The results are discussed in terms of reactor application; in particular, pool configuration, melt oxidation kinetics, critical influence of melt surface temperature and oxidation index on the fission product release rate, aerosol particle composition and size distribution. The relevance of measured high release of Sr from the molten pool for the reactor application is highlighted. Comparisons of the experimental data with those from the COLIMA CA-U3 test and the VERCORS tests, as well as with predictions from IVTANTHERMO and GEMINI/NUCLEA codes are made. Recommendations for further investigations are proposed following the major observations and discussions. © 2010 Elsevier B.V. All rights reserved.

Nd:YAG laser welding of high reflectivity metals is difficult because of the highly non-linear light-material interaction yielding a narrow process window and poor reliability. However, achieving high reliability is mandatory for applying this technique in industrial production lines. The welding control can be improved by real-time monitoring of the process evolution with sensors. Such sensor signals are particularly useful for weld classification and for laser power control in off-line or in closed-loop feedback configurations. The latter possibility is difficult to implement in pulsed lasers and requires a careful sensor choice. Here, we report on laser lap micro-spot welding of thin copper sheets using a pulsed Nd:YAG laser. The welding was performed under atmospheric conditions on pure, 50 mum thick, slightly oxidized copper sheets with pulse durations and energies of less than 8 ms and 8 J, respectively. The process was experimentally analyzed by detecting normal laser reflection, heat emission, and instantaneous laser power with high time resolution. The meaningful signal parameters have then been selected for a closed loop feedback control. The variance of top and bottom weld spot diameters could be reduced by more than a factor of 8 in the case of closed loop control.