Numerical Simulation and Experimental Results of in situ Heat Treated Austempered Ductile Iron

A model to predict the solidification of spheroidal graphite (SG) cast iron during cooling process was developed. The model treated the problem of the ternary Fe-C-Si system and aimed at simulating the evolution of the solidifying microstructure. When the eutectic temperature is reached, eutectic grains are formed. The rate of nucleation depends on the melt characteristics and supercooling. The nucleation rate was assumed to be presented by power law function of undercooling. The growth of the austenite grain was controlled by carbon diffusion through austenite. Carbon and silicon concentrations at different interfaces are calculated from the Fe-C-Si equilibrium ternary phase diagram and Sheil equation was applied to calculate the silicon content in the bulk liquid and the concentration of carbon in the liquid was determined to keep the eutectic reaction. The model was applied to a four-step cylindrical sand casting which has a different diameter. The simulated results were compared with the experimental ones using a post processing program which was also developed to simulate the microstructural evolution graphically. The results showed relatively good agreement and the usefulness of the proposed model was confirmed.

Accurate measurement of phase fraction distribution in gas-liquid-solid three-phase flow is critical for optimizing industrial processes such as petrochemical and bioengineering reactors. However, single-modality electrical tomography techniques face significant challenges due to complex flow dynamics, limited sensitivity, and the inability to simultaneously distinguish multiple phases with high precision. To address these limitations, this paper proposes a novel two-stage deep learning-based information fusion network that integrates electromagnetic tomography and electrical resistance tomography (ERT) data. The first-stage model (front-model) extracts the background liquid-solid phase fraction and corresponding empty-field ERT measurements, while the second-stage model (post-model) combines dual-modality data to reconstruct the solid phase fraction distribution. This approach effectively separates solid phase information from raw measurements and enhances image fusion quality. Simulation and experimental results demonstrate that the proposed model achieves high accuracy in predicting solid phase fractions, with a mean absolute percentage error of 1.53% in simulations and 5.2% in experiments. The model also exhibits strong noise robustness, maintaining performance at signal-to-noise ratios as low as 30 dB. This work advances the field by providing a reliable and non-invasive solution for phase fraction measurement in complex three-phase flow, with potential applications in industrial monitoring and control.

The role of phosphorus (P) in the heterogeneous nucleation of eutectic silicon (Si) and the evolution of eutectic grains in hypoeutectic aluminum-silicon alloys were investigated. Systematic additions of P in the range of 0.5 to 20 ppm to Al-7 wt pct Si alloys of different purities have shown that the morphology of the eutectic Si changes from a fine plate- to a coarse flake-like structure. The growth of eutectic grains was investigated by interrupting the eutectic reaction by quenching experiments. Moreover, the macroscopic growth mode of the eutectic grains was characterized by electron backscatter diffraction. An increase in P concentration from 2 to 3 ppm resulted in a transition of the macroscopic growth mode of the Al-Si eutectic in high purity alloys from growth with a planar front with a strong dependence of the thermal gradient, to nucleation in the vicinity of the primary Al dendrites and subsequent growth of distinct eutectic grains. It is suggested that AlP particles are the key impurities acting as potential nucleation sites for eutectic Si. This is further substantiated as with increasing P concentration nucleation and growth of the Al-Si occurred at higher temperatures close the equilibrium Al-Si eutectic solidification temperature at 850 K (577 °C). In addition, the recalescence undercooling ΔT R,eu was reduced from 4.5 K (0.5 ppm P) to 1.5 K (20 ppm P) in high purity alloys. This was accompanied by a drastic increase of the nucleation rate of the eutectic grains.

The graphite nodule count, size distribution and homogenization of the nodules distribution are the factor which are of more significance for the properties of the material. By just increasing the inoculants or Mg will not help to get rid of problems like the un-even size distribution and or increasing the nodule count. The cooling conditions of the melt prior to solidification and during solidification can control these two parameters to a large extent. In this research, it is more emphasized on the nucleation sequence of MgO particles and on the cooling rates. The nucleation of MgO at different temperatures and at different cooling rates was found to have a great influence on the nodule size distribution and the homogenization of the microstructure. A mathematical model was derived to relate the Mg concentration in the liquid to the cooling rate, prior to solidification. The MgO particles count was calculated as a function of cooling rate. It was found that at higher cooling rates, MgO can be nucleated in multi steps during cooling process, which can increase the nodule count tremendously.

The determination of silicon and carbon contents by thermal analysis is based on the recording of a cooling curve of a melt whose eutectic solidification takes place in the metastable system. The temperatures of the austenite and eutectic arrests are evaluated and then related to the carbon and silicon contents by linear relationships that would be defined by the phase diagram if there were no undercoolings. However, published experimental values of austenite liquidus arrest and metastable eutectic arrest both show significant undercoolings when compared to the equilibrium metastable Fe–C–Si phase diagram. The undercooling of the austenite observed in hypo-eutectic alloys can be explained by tip undercooling during dendritic growth. On the other hand, it is pointed out that alloys with a composition close to the stable eutectic—either slightly hypo- or slightly hypereutectic—can show much higher undercoolings than expected if some stable eutectic precipitates. For such compositions, the thermal analysis could hardly be reproducible enough if the alloy does not solidify completely in the metastable system. Furthermore, the published experimental information on the temperature of the metastable eutectic is here supplemented by new results for silicon contents up to nearly 4 wt%. Both previous and new results show a similar undercooling of 5 to 15 °C compared to the calculated equilibrium metastable eutectic. Each foundry wishing to use thermal analysis for carbon and silicon evaluation must determine its own relationships for austenite liquidus and metastable eutectic to account for the specificity of its melting process and casting system. Care should be taken to avoid any graphite precipitation in the thermal cup, and testing should be performed to improve reproducibility as this defines the accuracy of the composition determination.

A plasma native oxide cleaning process is widely used on the semiconductor production line to remove oxide impurities on silicon surfaces of an wafer. In this study, a flow simulation with microwave plasma species has been conducted to analyze the flow characteristics in a showerhead that affect the batch uniformity in the process. In particular, the distributions of temperature and mass flow rate of the gas as well as the number density of hydrogen radicals at the showerhead hole outlets were compared for different showerhead designs by using computational fluid dynamics. The distribution of gas temperature at the hole outlets was found to be inversely proportional to one of gas mass flow rate by the simulation results. However, mass flow rate distribution for the total gas shows a different trend from one of hydrogen radicals in the showerhead hole outlets. The showerhead design with low temperature gradient also showed a more uniform mass flow rate profile at the hole outlets, which was validated by the simulation results.

As the Zizania latifolia has a delicious taste, high nutritional value and rich moisture, it is easy to rot and deteriorate due to the high moisture content, resulting in short shelf life. In order to maintain quality of Zizania latifolia, the vacuum cooling process of cylindrical vegetables is experimentally studied. Considering the transient heat transfer and mass conservation, a mathematical model of heat and mass transfer in the vacuum cooling process of cylindrical vegetables is established. Meanwhile, the temporal trends of total system pressure, temperature distribution, evaporation rate of water, weight loss and moisture content of Zizania latifolia are simulated by CFD software. The experimental data are compared with the CFD simulation results. It is found that the differences of the temperature between the simulation and the experiments are 4.7%. The amount of water evaporated from the Zizania latifolia by simulation is 5.5% during the whole vacuum cooling, while the tested water loss rate is 9.8%, the maximal deviation of weight loss is within 4%. The simulated result of 83.5% after a cooling time of 850 s, gives a reasonable agreement with the experimential moisture content of 86.7% in the same cooling period. The results show that the CFD simulation values agreed well with the experimental data. It is significant for the study of the water transfer characteristics of cylindrical vegetables tissue and the optimization of the vacuum cooling process of the food industry.

Density change occurring in ductile iron castings is a phenomenon far more complicated than in other casting alloys. Initially, graphite nodules grow directly from liquid phase. That is the reason for decrease in alloy density and casting expansion. Decaying carbon concentration in liquid phase adjacent to graphite nodules favours growth of austenite, which covers them isolating from the liquid. In order for graphite to grow further diffusion of carbon through thickening solid solution layer is needed. At this time expansion fades and shrinkage begins. Industrial experience shows that whether or not shrinkage defects in ductile iron castings will occur depends on wall thickness.In the paper an attempt to identify mechanism of shrinkage porosity formation in nodular iron castings during solidification was made. To that end a two-dimension simulation of binary Fe-C system solidification by cellular automaton method was carried out. Using data obtained with Thermo-CALC software, dependencies of temperature on density for each present phase were determined. For liquid phase and austenite influence of carbon concentration on density was also appended. Applying those relationships to the model, density of each individual cell of used grid as well as mean value for whole analysed region were assessed. The method allowed to consider volume fractions of phases and heterogeneity of solid and liquid solutions to find the mean density of the material.The paper presents results of computer simulation of nodular iron density change, with eutectic saturation of 0,9 to 1,1.

HighlightsA temperature distribution occurred due to temperature differences between the surface and inside passion fruit seeds.The temperature distribution occurred simultaneously in all directions.The temperature distribution decreased at greater depths inside the seeds.The same temperature distribution pattern occurred in the vertical and horizontal directions.Abstract. Optimization of the drying process can be determined based on temperature distribution patterns using numerical analysis with the finite element method (FEM). This study compiled a numerical analysis using FEM to predict the temperature distribution in passion fruit seeds during drying. The study was conducted using a circulating-air tray dryer. Temperature distribution data on passion fruit seeds were measured using a data logger. The results showed that numerical analysis using FEM quickly and accurately simulated the temperature distribution in passion fruit seeds during drying. The model was validated by comparing the temperature distribution data measured in the drying chamber with the simulation results, with a relative error of 0.45% to 1.27%. Numerical analysis using FEM provides an useful reference for controlling temperature distribution during drying because this method is easy to implement and results in low errors. Keywords: Drying, Finite element methods, Numerical analysis, Passion fruit seeds, Temperature distribution.

We present and compare numerical simulations and experimental data for Quasi-Steady State (QSS) and transient photoconductance lifetime measurements on silicon ingots. The simulation results show that the QSS method is generally more accurate for lifetimes below 150 μs, whereas transient measurements are more accurate above this value. However, transient measurements require sufficient time to have elapsed after the flash is terminated, to ensure that the impact of the unpassivated ingot surface is reduced. The results also show that the surface recombination velocity has a slightly reduced impact on n-type material in comparison with p-type material, due to the reduced minority carrier mobility. The simulation results are also compared with measured QSS and transient lifetimes on a standard p-type monocrystalline block.

Characterization of multiphase flow in bubble columns using KT-1 signature and fractal dimension

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In this paper, the small signal stability of a Battery Energy Storage System (BESS) used in a low voltage islanded microgrid is investigated for an ohmic load case using eigenvalue sensitivity analysis. Two approaches namely Quasi Steady State (QSS) and Dynamic Phasor Modeling (DPM) are presented and compared for a reference BESS in a real microgrid. The QSS approach is considered as a traditional method to model system dynamics assuming that they are slow enough to apply steady state rules. The DPM approach on the other hand considers the electrical dynamics in the control feedback loop and the coupling between the parallel inverters. The evaluation of the mathematical models for both approaches as well as simulation and measurement results are presented. The classical QSS stability analysis applied to the BESS does not show the dependency of stability margins on droop parameters, smoothing time constant or load parameters. This problem can be overcome by the presented DPM method. The sensitivity of the BESS and load parameters on stability limits is studied in detail.

Phase change of steel during cooling affects the slab qualities in continuous casting. Especially, crack susceptibility of hypo peritectic steel is high because large volume shrinkage occurs by peritectic phase transformation during solidification and cooling. In continuous cooling, phase change is different from the behaviors under the equilibrium condition, such as undercooling and extend of peritectic reaction, etc. Therefore, we develop a new phase change model considering thermodynamics, empirical equations, and carbon diffusion in each phase to predict phase change behavior during continuous cooling. In this model, phase change of hypo peritectic steel comprises 5 stages until all phases become the γ phase. The velocities of the δ/γ interface and phase fractions during cooling are calculated according to cooling rate, undercooling of the γ phase, and carbon contents. The results show that if solidification ends by the δ phase during dTp, the γ phase is formed by massive transformation. On the contrary, if peritectic reaction starts with liquid, the γ phase is formed and grows by diffusional transformation. In latter case, massive transformation of remaining δ phase can occur with high undercooling or very fast cooling rates. This analysis shows that there are several different paths depending on carbon contents of hypo peritectic steels. Phase change of hypo peritectic steel.

In this study, a 3-D CFD simulation and laser diagnostics were developed to understand the characteristics of soot generation in a diesel diffusion flame. The recently developed RANS (Reynolds-averaged Navier-Stokes equations) hybrid combustion model (Extended Coherent Flame Model — 3 Zones, ECFM-3Z model) was used. This industrial, state-ofthe-art model of the diffusion flame is commonly used in diesel combustion models as well as for propagating (premixed) flame combustion. The simulation results were validated with measurements from a constant volume combustion chamber. The experiment revealed that soot accumulated in the chamber where the temperature decreased. Where the temperature increased rapidly, only a little soot accumulated. The temperature and soot distribution were independently examined using both the two-color method and a 3-D CFD simulation for a turbulent diesel diffusion flame.