This work presents an efficient method to quickly calculate with good accuracy (about 5%) the solidification time of an injected semi-crystalline polymer slab. Under some hypotheses this polymer can be considered as a phase change material with a constant phase change temperature. We use a noteworthy property established on the ratio between the thickness of a solidifying phase change finite medium and the solidified thickness in a semi-infinite medium. The knowledge of this ratio enables to predict analytically the solidification time in a 1D finite medium. This ratio can be parameterized as a function of characteristic numbers in phase change problems: Stefan numbers and the ratio of thermal diffusivities of both phases. The results are compared with those given by a complete model integrating the physics of the coupling between heat transfer and crystallization kinetics. The solidification times computed from both models are very close, demonstrating the relevance of the simplified model. Finally, we also get a very good accuracy in calculating the total cooling time, from injection to ejection.

As the first step of simulation, a temperature field for solidifying cast steel and cast iron roll was created. The convection in the liquid is not comprised since in the first approximation, the convection does not influence the analysed occurrence of the C → E (columnar to equiaxed grains) transition in the roll. The obtained temperature field allows to study the dynamics of its behavior observed in the middle of the mould thickness. This midpoint of the mould thickness was treated as an operating point for the C → E transition. A full accumulation of the heat in the mould was postulated for the C → E transition. Thus, a plateau at the T ( t ) curve was observed at the midpoint. The range of the plateau existence t C ↔ t E corresponded to the incubation period, t C R ↔ t E R that appeared before fully equiaxed grains formation. At the second step of simulation, the thermal gradients field was studied. Three ranges were distinguished: a/ for the formation of the columnar structure (the C–zone): ( T ˙ ≫ 0 and ( G | t < t C R − G | t = t C R ) ≫ 0 ) , b/ for the C → E transition (from columnar to fully equiaxed structure): ( T ˙ ≈ 0 and ( G | t = t C R − G | t = t E R ) ≈ 0 ) , c/ for the formation of the fully equiaxed structure (the E–zone): ( T ˙ < 0 and ( G | t = t E R − G | t > t E R ) ≈ 0 ) . The columnar structure formation was significantly slowed down during incubation period. It resulted from a competition between columnar growth and equiaxed growth expected at that period of time. The ( G | t = t C R − G | t = t E R ) ≈ 0) relationship was postulated to correspond well with the critical thermal gradient, G crit. . A simulation was performed for the cast steel and cast iron rolls solidifying as if in industrial condition. Since the incubation divides the roll into two zones (columnar and equiaxed) some experiments dealing with solidification were made on semi-industrial scale. A macrosegregation equation for both mentioned zones was formulated. It was based on a recent equation for redistribution after back-diffusion. The role of the back-diffusion parameter was emphasized as a factor responsible for the redistribution in columnar structure and equiaxed structure.

Effects of different parameters on the melting, vaporization and resolidification processes of thin gold film irradiated by a femtosecond pulse laser are systematically studied. The classical two-temperature model was adopted to depict the non-equilibrium heat transfer in electrons and lattice. The melting and resolidification processes, which was characterized by the solid-liquid interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, was obtained by considering the interfacial energy balance and nucleation dynamics. Vaporization process which leads to ablation was described by tracking the location of liquid-vapor interface with an iterative procedure based on energy balance and gas kinetics law. The parameters in discussion include film thickness, laser fluence, pulse duration, pulse number, repetition rate, pulse train number, etc. Their effects on the maximum lattice temperature, melting depth and ablation depth are discussed based on the simulation results.

In this paper, we performed a numerical study on the effects of thermal shrinkage on deposition of molten tin and nickel droplets on a steel substrate in thermal spray processes using Volume-of-Fluid (VOF) method. Thermal shrinkage is a phenomenon caused by variation of density during solidification and cooling of molten metals. In our model, the Navier-Stokes equations along with energy equation including phase change are solved using a 2-D axisymmetric mesh. We used the VOF method to track the free surface of droplet. For solidification, we used an enthalpy-porosity formulation. The simulations performed in this study are accomplished using a commercial code (Fluent). Results of these scenarios are presented: the normal impacts of 2.7mm tin droplets at 1m/s and 2m/s, initially at 240°C, onto a 27°C steel substrate. When the droplet impacts the substrate with a velocity of 1m/s, the final splat has a single cavity inside due to shrinkage. In other cases with the scales of a typical thermal spray process, the results of normal impact of nickel droplets with a velocity of 73m/s, initial temperature 1600°C and diameter 60μm to steel substrate with different temperatures are presented. In these cases shrinkage decreases the droplet splashing on the substrate.

This lecture is dedicated to the memory of Professor Eddie Leonardi, formerly International Heat Transfer Conference (IHTC-13) Secretary, who tragically died at an early age on December 14, 2008. Eddie Leonardi had a large range of research interests: he worked in both computational fluid dynamics/heat transfer and refrigeration and air-conditioning for over 25 years. However starting from his PhD ‘A numerical Study of the effects of fluid properties on Natural Convection’ awarded in 1984, one of his main passions has been natural convection and therefore the focus of this lecture will be on what Eddie Leonardi has achieved in numerical and experimental investigations of laminar natural convective flows. A number of examples will be presented which illustrate important difficulties of numerical calculations and experimental comparisons. Eddie Leonardi demonstrated that variable properties have important effects and significant differences occur when different fluids are used, so that non-dimensionalisation is not an appropriate tool when dealing with fluids in thermally driven flows in which there are significant changes in transport properties. Difficulties in comparing numerical solutions with either numerically generated data or experimental results will be discussed with reference to two-dimensional natural convection and three-dimensional Rayleigh-Be´nard convection in bounded domains with conducting boundaries. For a number of years Eddie Leonardi was involved in a joint US-French-Australian research program — the MEPHISTO experiment on crystal growth — and studied the effects of convection on solidification and melting under microgravity conditions. The results of this research will be described. Finally, results of experimental and numerical studies of natural convection for Building Integrated Photovoltaic (BIPV) applications in which Eddie Leonardi had been working in the last few years will also be presented.

Experiments have been conducted into the unidirectional freezing of an aqueous solution of winter flounder antifreeze protein 0.02mm thick. It is confirmed that the instantaneous temperature field can be measured with a near-infrared camera. It is found that the difference between the conduction heat flux of pure water near the interface and that of ice is approximately equal to the heat flux for solidification, which is the product of ice density, interface velocity and the latent heat of fusion. The sum of the conduction heat flux of protein solution near the front edge of the serrated interface and the heat flux for solidification is approximately equal to the conduction heat flux of ice. On the other hand, the sum of the conduction heat flux of protein solution near the bottom edge of the serrated interface and the heat flux for solidification is much higher than the conduction heat flux of ice.

The hydrodynamics of molten metal jet in a coolant pool is characterized by the presence of complex and diverse fluid structures whose formation is facilitated by various modes of instabilities acting on the fluid-fluid interface and the bulk material. The large spectrum of scales involved in these processes and the related non-linearities cloud a clear understanding of the associated physical phenomena. In order to overcome these difficulties, a numerical model has been developed in the current work, which aims to simulate the hydrodynamics, fragmentation and solidification of a molten metal jet in the coolant pool. The work uses an axisymmetric flow solver with the Volume of Fluid (VOF) interface tracking model to evaluate the macro features of the molten metal jet dynamics and to predict the evolution of interfacial instabilities. At the same time, the phenomena at the micro scale is predicted by a Lagrangian particle tracking model that is used to capture the dynamics and the heat interactions of the fragmented droplets formed from the disintegration of molten metal jet. The coupling between the two models is achieved by converting the molten fluid from VOF model into equivalent swarm of particles at the jet breakup length. The ability of the current coupled model is demonstrated using a sample test problem involving the dynamics of molten woods metal jet in a water pool.

In the current study the effects of vibration on the solidification process of phase change material (PCM) paraffin in a sphere shell are investigated. The amount of PCM used was kept constant during each experiment by using a digital scale to check the weight and a thermocouple to check the consistency of the temperature. A small amount of air was present in the sphere so that the sphere was not filled completely. Commercially available paraffin wax, RT35, was used in the experiments. Experimentations were done on a sphere of 40 mm diameter, wall temperature of 20°C below mean solidification temperature, and consistent initial temperature. A constant vibration frequency of 100 Hz was applied to the setup and results compared with that of no vibration. Samples were taken at different times during the solidification process and compared with respect to solid material present. It was found that the solidification time had been reduced significantly under the vibration. This led to the conclusion that there had been an improvement in heat transfer due to the vibration.

Electrical initiation of solidification from supercooled state and preservation of supercooled state of sodium acetate trihydrate solution, which is considered as a promising thermal energy storage material, are experimentally investigated with varying the configuration of electrodes and confirmed that the initiation of solidification and preservation of supercooled state are both possible by using the electric field. Further, effect of crystal growth direction on crystal growth rate is also investigated by using the newly developed electrical nucleation method. The result shows that the crystal growth rate, which growth direction is bottom to top, is slightly decreased compared with the direction of top to bottom at certain supercooling temperature range.