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This study employed optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to investigate the impact of vanadium (V) on the microstructure and mechanical properties of gray cast iron (GCI) HT250. Additionally, Thermo-Calc software was employed to explore the influence of V on the solidification process. The results indicate that adding trace amounts of V in GCI forms a face-centered cubic VC phase, with the precipitation temperature of the VC phase gradually increasing. When the V content reaches 0.28 wt%, the VC phase begins to precipitate during the eutectic reaction. The incorporation of V consumes carbon, reducing the graphite content and promoting the formation of type D graphite. As the V content increases, there is an enlargement in the pearlite area ratio, a decrease in the pearlite layer spacing, and a reduction in the size of eutectic cells. These microstructural alterations lead to enhanced mechanical properties. The tensile strength peaks at 336 MPa with a V content of 0.77 wt%, representing a 29% increase compared to samples without added V. Similarly, the Vickers hardness increases with increasing V content, reaching a peak of 373 HV at 0.92 wt% V, a 27% increase compared to samples without V addition. However, at this point, the tensile strength decreases to 322 MPa.

The solidification process of Ni-based superalloy K465 was examined using DTA and X-ray diffraction. The impact of melt structure on solidification process and the morphology of MC carbide and γ′-phase was analyzed. It was observed that an increase in melt peak temperature led to a significant decrease in precipitation temperature for carbides, but only a slight increase in the formation temperature of matrix and eutectic microstructure. The X-ray diffraction results showed that some ordered structures were detected in the sample with melt peak temperature of 1450 °C and 1500 °C, but not in the sample with melt peak temperature of 1360 °C. Furthermore, the ordered structure displayed similar crystalline features with M6C carbide. As the melt peak temperature increased, the carbides changed from block type to script type morphology. This phenomenon was likely caused by the formation of ordered structures at high temperatures. However, the microstructure of γ matrix and γ′ precipitates remained unaffected by the melt peak temperature.

Macrosegregation and shrinkage porosity in large steel ingots are key factors restricting the homogenization of large cast and forged parts. Due to the complex mechanisms of their formation, they have always been challenging issues in the research on solidification control of large steel ingots. The purpose of this review is to systematically revisit the research progress on the mechanisms of macrosegregation and shrinkage porosity formation in large steel ingots, focusing on the mechanisms of formation of 'A' type segregation, positive segregation at the top, and negative segregation at the bottom, and their impact on the quality of steel ingots. At the same time, the conditions and influencing factors for the formation of shrinkage porosity are analyzed in detail, and the interaction between macrosegregation and shrinkage porosity during the solidification process of steel ingots is discussed. Based on existing research results and challenges, prospects for future research directions are proposed, emphasizing the development of high-precision numerical simulation techniques and experimental research methods to deeply understand the internal mechanisms of segregation and porosity formation, providing a scientific basis for formulating effective control strategies. [ABSTRACT FROM AUTHOR]

A new apparatus was built to rapidly cool molten salts in liquid argon to prevent contamination during quenching and enable new insight into the structure in the liquid state. To test the applicability of the apparatus, several industrially relevant chloride salt compositions were first melted, rapidly solidified, and then characterized. The design proved applicable for the rapid quenching of molten salt. Furthermore, the structure of the apparatus prevented exposure of the rapidly quenched salt to impurities (humidity, oxygen, etc.). X-ray diffraction of salt specimens cooled with and without liquid argon showed differences including a structure further from the expected stoichiometric equilibrium with rapid cooling. Of particular interest is the chemical state of metallic impurities, and this may be probed using electron paramagnetic resonance. [ABSTRACT FROM AUTHOR]

Manganese sulfide inclusions are more common in heavy rail steel, and it is very important to control the sulfide in heavy rail steel. In this paper, an optical microscope, scanning electron microscope, etc., are used to construct a three-dimensional model analysis of inclusions in U75V rail, and the precipitation law of MnS is obtained by combining Thermo-calc software and the growth coupling prediction model. The results show that the inclusion types in the U75V rail are mainly composite inclusions with magnesia-alumina spinel as the core and MnS on the periphery. The inclusions are elongated along the rolling direction, and the inclusions at the rail head and rail bottom are more slender, with an average aspect ratio of 9.10 and 7.48, while the inclusions at the rail waist are relatively flat, with an average aspect ratio of 5.92. Considering the precipitation of inclusions and the segregation of solute elements, it is found that MnS precipitates when the concentration product of Mn and S exceeds the equilibrium value, and reducing the S content is a reasonable choice to prevent the precipitation and growth of MnS. [ABSTRACT FROM AUTHOR]

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed. [ABSTRACT FROM AUTHOR]

The effects of vanadium addition on the solidification microstructure and mechanical properties of Al–4Ni alloy were investigated via thermodynamic computation, thermal analysis, microstructural observations, and mechanical properties testing. The results show that the nucleation temperature of primary α-Al increased with increased vanadium addition. A transition from columnar to equiaxed growth took place when adding vanadium to Al–4Ni alloys, and the average grain size of primary α-Al was reduced from 1105 μm to 252 μm. When the vanadium addition was 0.2 wt%, the eutectic nucleation temperature increased from 636.2 °C for the Al–4Ni alloy to 640.5 °C, and the eutectic solidification time decreased from 310 s to 282 s. The average diameter of the eutectic Al3Ni phases in the Al–4Ni–0.2V alloy reduced to 0.14 μm from 0.26 μm for the Al–4Ni alloy. As the vanadium additions exceeded 0.2 wt%, the eutectic nucleation temperature had no obvious change and the eutectic solidification time increased. The eutectic Al3Ni phases began to coarsen, and the number of lamellar eutectic boundaries increased. The mechanical properties of Al–4Ni alloys gradually increased with vanadium addition (0–0.4 wt%). The Al–4Ni–0.4V alloy obtained the maximum tensile strength and elongation values, which were 136.4 MPa and 23.5%, respectively. As the vanadium addition exceeded 0.4 wt%, the strength and elongation decreased, while the hardness continued to increase. Fracture in the Al–4Ni–0.4V alloy exhibited ductile fracture, while fracture in the Al–4Ni–0.6V alloy was composed of dimples, tear edges, and cleavage planes, demonstrating mixed ductile–brittle fracture. The cleavage planes were caused by the primary Al10V and coarse Al3Ni phases at the boundary of eutectic cells. [ABSTRACT FROM AUTHOR]

In a cylindrical shell and multi-tube heat exchanger (of large configuration), the incorporation of four distinct nanoparticles (Al2O3, MgO, SiO2, and SnO2) at various concentrations (0%-5%, v/v) into PCM (RT82) was investigated during the solidification process. A numerical model was developed and validated through experimental and theoretical findings found in literature. Whatever the metal oxides' concentration, a clear enhancement of the freezing rate of PCM was observed over its solidification period, where this improvement was boosted proportionally with the rise of metal oxides concentration. However, the worst performance of the nano-PCM system was obtained using SnO2 nanoparticles, where a total solidification of PCM is observed after 26000 s for 5% (v/v) SnO2. In contrast, the best performance was resulted using SiO2, for which a total hardening of PCM was reached after 21000 s for 5% (v/v) silicon dioxide. This means that a reduction of 19.23% of the freezing period was obtained using SiO2 compared to SnO2 system at the same volume fraction (5%). It was found that in presence of nanoparticles (nano-PCM system), the solidification rate of PCM is in the order: SiO2>MgO> Al2O3>SnO2. According to the thermophysical properties of metal oxides, it was found that the enhancing role of nanoparticles (toward PCM solidification) is density-dependent. Therefore, the effect of heat capacity may be overlooked. [ABSTRACT FROM AUTHOR]

Titanium oxides, which act as nuclei for intragranular ferrite (IGF), are common inclusions in low‐carbon steel. The interlocking structure of IGF greatly improves the mechanical properties of low‐carbon steel. To make the best use of this kind of oxide, the types, sizes, and distribution properties of effective titanium oxides are reviewed that can promote IGF nucleation. The control techniques of titanium oxides are summarized as follows: (1) Ti2O3 is one of the most effective of the common titanium oxides, followed by TiO and TiO2. The type of titanium oxide can be affected by controlling the Ti/O mass ratio in molten steel. (2) Titanium oxide with a size range of 0.4–4 μm can effectively promote the nucleation of IGF or intragranular acicular ferrite (IAF), among them, titanium oxide of about 1 μm is the most beneficial to IAF nucleation. (3) To obtain titanium oxides with effective size, the precipitation of titanium oxides should be controlled during the solidification process, and this process can be achieved with the existing rapid solidification technology. Under the same conditions, the higher solidification rate can obtain finer titanium oxide. [ABSTRACT FROM AUTHOR]

Metal foam (MF) and nano-sized particles (NSP) are regarded as patent tools for enhancing the thermal performance of phase change materials (PCM)-based latent thermal energy storage unit (LTES), but data on this issue for large-scale installations is very scarce. This study provides a comprehensive computational analysis of the effects of MF and NSP on the solidification process of RT82 paraffin (PCM matrix) in a large-scale shell-and-tube latent thermal energy storage unit (of heat exchanger form). The developed 2D transient model developed on Ansys Fluent 15.0 software was initially verified using available literature experimental data. The process performance was tested for 5% Al2O3 nanoparticles and various MFs [i.e. aluminum (Al), copper (Cu), nickel (Ni) and titanium (Ti)] with varied porosity (96–100%). The computed mean and spatial temperature and solidified degree of the PCM block showed a drastic acceleration of the solidification process with the b MF technique rather than with the nanoparticles system. The solidification performance increased in the direction of MF-thermal conductivity increase, i.e. Cu > Al > Ni > Ti, and material porosity decrease. These conditions allow rapid HTF heat recovery and then stocking considerable thermal energy. However, the MF porosity could not decrease below 95% to avoid a huge loss of material storage (PCM), thereby diminishing the thermal storage capacity of the LTES unit. [ABSTRACT FROM AUTHOR]

The melting/solidification of PCM "phase change material" (C19-C20) and cooling/heating of air (HTF "heat transfer fluid") have been analyzed under the variation of temperature, by an increment of 2 K, on the external side of the heat exchanger (Tw). Aluminum foam (20%, v/v) was used to improve the thermal conductivity of the adopted PCM (C19-C20). Eight cases were investigated during the melting (Tw: from 310 to 324 K) and solidification (Tw: from 284 to 298 K) periods of PCM (C19-C20). It has been shown that the melting/freezing processes of PCM were enhanced by increasing (from 310 to 324 K)/decreasing (from 298 to 284 K) the temperature on the external side of the heat exchanger. On the other side, the cooling/heating mechanisms of air were found to be less dependent on the temperature of the external side of the thermal unit. Additionally, it was observed that the decreasing/increasing of air (HTF) temperature were more rapid than the fusion/freezing processes of PCM. Based on the mass fraction profiles of the liquid PCM, it was retrieved that the fusion and solidification mechanisms proceeded in a quasi-homogeneous way as the melting or freezing of PCM were observed to take place gradually all around the center of the heat exchanger. Compared to the fusion process of PCM, its freezing regime was observed to be slower. [ABSTRACT FROM AUTHOR]

The real-time observation of molten materials and their cooling to solid state is of importance for many industrial processes. In this work, we describe additional possibilities obtained by the implementation of a Rapid Scan technique on an FT-IR emissometer designed to allow the observation of materials under extreme temperature conditions. The possibility of following liquid-to-solid state phase transition mechanisms through time-resolved emissivity will be illustrated. This new methodology presents interesting possibilities for the study of structural transformations through the real-time monitoring of the dielectric function and true sample temperature of the experimental emissivity spectra acquired every 50 ms under free cooling conditions. [ABSTRACT FROM AUTHOR]

The effects of Y on the solidification process of 7Mo super austenitic stainless steel (7MoSASS) under low cooling rate conditions (10 °C/min) were investigated using high-temperature confocal laser scanning microscopy (HT-CLSM). The in situ observation results indicate that Y samples promote an increase in austenite nucleation density. After 10 s of nucleation, the nucleation density increased by 149.53/mm2 for the Y sample. Furthermore, variance analysis indicated that Y addition improved the uniformity of the 7MoSASS solidification microstructure under low cooling rate conditions. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory results showed that when the solid phase ratio was 0.5, the nucleation mode of the Y sample transitioned from saturation site nucleation to saturation site nucleation + Avrami nucleation. YAlO3 has a low lattice disregistry value with austenite, making it a suitable heterogeneous nucleation core for promoting the early nucleation of austenite. During the late stages of solidification, Y accumulates in the residual liquid phase, providing a greater degree of compositional undercooling. SEM-EDS analysis showed that Y contributed to the refinement of the 7MoSASS solidification microstructure, with the proportion of precipitated phases decreasing by approximately 7.5%. Cr and Mo were the main elements exhibiting positive segregation in 7MoSASS, and the Cr segregation ratio increased in the Y sample, while the Mo segregation ratio decreased. [ABSTRACT FROM AUTHOR]

Solidification structure is a key aspect for understanding the mechanical performance of metal alloys, wherein composition and casting parameters considerably influence solidification and determine the unique microstructure of the alloys. By following the principle of free energy minimization, the phase-field method eliminates the need for tracking the solid/liquid phase interface and has greatly accelerated the research and development efforts geared toward optimizing metal solidification microstructures. The recent progress in the application of phase-field simulation to investigate the effect of alloy composition and casting process parameters on the solidification structure of metals is summarized in this review. The effects of several typical elements and process parameters, including carbon, boron, silicon, cooling rate, pulling speed, scanning speed, anisotropy, and gravity, on the solidification structure are discussed. The present work also addresses the future prospects of phase-field simulation and aims to facilitate the widespread applications of phase-field approaches in the simulation of microstructures during solidification. [ABSTRACT FROM AUTHOR]

The effect of Ca element on the microstructure evolution of the AZ91 magnesium alloy was investigated in this research. The magne-sium-aluminium alloy AZ91 was inoculated with the Emgesal® Flux 5 to refine its microstructure and also improve its microstructure. Six different concentrations of the Emgesal® Flux 5 content were tested, ranging from 0.1 to 0.6% wt., and compared to the baseline of the AZ91 alloy without inoculation. Melted metal was poured into a preheated metallic mould. Samples to test were achieved after turning treatment. Formed microstructure was assessed using an optical microscope. The microstructure was refined for every tested samples. Me-chanical properties such as tensile strength, elongation, Brinell hardness, Vickers microhardness, abrasion resistance and adhesive resistance were tested on the inoculated samples and compared to the non-inoculated AZ91. Introducing an Emgesal®Flux 5 inoculant caused a change in the tensile strength, elongation, Brinell hard-ness, Vickers microhardness, abrasive wear resistance as well as adhesive wear resistance in each examined concentration.

Nowadays, due to the features such as high latent heat and constant phase transition temperature, the utilization of phase change materials (PCMs) in energy storage and thermal management systems has attracted scholars' attention. However, the low thermal conductivity and solidification process of these materials has always been a challenge for widespread implementation of them in disparate industries. The current research investigates the characteristics of the PCM solidification process within a triplex tube Latent Heat Thermal Energy Storage System (LHTESS) with innovative hollow fins in the presence of ternary hybrid nanoparticles (THNPs) and radiative heat transfer. The governing equations are solved using Galerkin Finite Element Method (GFEM) with various boundary conditions in the outer wall, such as constant temperature, adiabatic, and coolant fluid temperature (triplex), through FlexPDE software. Furthermore, the effect of key parameters, including shape factor and volume fraction of THNPs, and radiative heat transfer on thermal storage performance is scrutinized. Ultimately, the Taguchi method is adopted to determine the optimal point at which the full solidification time (FST) is lowest. Results show that at 400000 s, the triplex case improved total discharging energy by 23% and 4% in comparison to the constant temperature and the adiabatic case, respectively. Additionally, by including THNPs with a volume percentage of 0.1 and a shape factor of 16.1 instead of 3, the required time for FTS reduces by approximately 13.1% and 21.9%, respectively. Also, the overall solidification times of the PCMs decrease to 36% by enhancing the radiation parameter from 0 to 1. These outcomes illustrate THNPs and considered fins are effective for reducing the FST and the shape factor of THNPs and radiation are key parameters that should be considered by designers.

Modification of the eutectic silicon in Al–Si alloys causes a structural transformation of the silicon phase from a needle-like to a fine fibrous morphology and is carried out extensively in the industry to improve mechanical properties of the alloys. The theories and mechanisms explaining the eutectic modification in Al–Si alloys are considered. We discuss the mechanism of eutectic rubidium modification in the light of experimental data obtained via quantitative X-ray spectral microanalysis and thermal analysis. X-ray mapping revealed that rubidium, which theoretically satisfies the adsorption mechanisms of silicon modification, had an effect on the silicon growth during solidification. Rubidium was distributed relatively homogeneously in the silicon phase. Microstructural studies have shown that rubidium effectively refines eutectic silicon, changing its morphology. Modification with rubidium extends the solidification range due to a decrease in the solidus temperature. The highest level of mechanical properties of the alloy under study was obtained with rubidium content in the range of 0.007–0.01%. We concluded that rubidium may be used as a modifier in Al-Si eutectic and pre-eutectic alloys. The duration of the modifying effect of rubidium in the Al-12wt%Si alloy melt and porosity in the alloy modified with rubidium were evaluated. [ABSTRACT FROM AUTHOR]

Bulk metallic glasses (BMGs) bear versatile advantages compared to traditional crystalline metallic materials. However, preparation of large size BMG components remains a great challenge due to the lack of understanding the casting dynamics of BMGs. The present work investigates the dynamics of the solidification process during casting of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG by measuring the time-dependent temperature evolution and constructing distance–time curves showing the progress of solidification. The experimentally probed temperature evolution proves that a higher casting temperature causes a lower cooling rate and induces more pronounced nanocrystal phase formation in the final BMG casting. Thus, optimization of the casting temperature is crucial for casting BMG components. The solidification coefficient K of the studied Zr-based BMG in copper mold was determined. The solidification time can be calculated with model: τ=M2K2. The solidification of the Zr-based BMG occurs in a narrow transition layer region following a “layer-by-layer” solidification mode. This feature is vital for designing the casting process appropriately to avoid the formation of casting defects in BMG components. The present work sheds new light on the solidification mechanism of bulk glass-forming liquids and underlines the importance of optimizing the technology and processing conditions for fabrication of BMG components with practical applications.

One of the likely methods for enhancing heat transfer in a latent thermal energy storage system is the conception of a thermal unit. In this study, the orientation of oval tubes (horizontal, vertical, and oblique) in phase change material (PCM, C19-C20)-based shell-tube heat exchanger was analyzed with respect to the metal foam (MF) type (graphite, copper, and nickel) in comparison to the case of pure PCM. For this purpose, a two-dimensional mathematical model was developed to investigate the thermal efficiency of the PCM-metal foam based composite energy storage unit. It was concluded that the orientation of the oval tubes (oblique, horizontal, and vertical) has a negligible impact on the performance of the thermal unit during the melting/solidification processes. Based on the liquid/solid fraction, total enthalpy and the average temperature in the annular space, the performance of a heat exchanger during fusion/solidification periods is in the order: copper-MF > graphite-MF > nickel-MF > pure PCM. Whatever the adopted MF or the geometry of tubes, the melting process is expedited compared to the solidification mechanism.

Due to the importance of uranium and uranium alloys to national defence and nuclear industrial applications, it is necessary to understand dendrite formation in their solidification structures and to control their microstructures. In this study, a modified cellular automaton model was developed to predict 2-D and 3-D equiaxed dendrite growth in U-Nb alloys. The model takes into account solute diffusion, preferential growth orientation, interface curvature, etc., and the solid fraction increment is calculated using the local level rule method. Using this model, 2-D large-scale and 3-D equiaxed dendrite growth with various crystallographic orientations in the U-5.5Nb alloy were simulated, and the Nb micro-segregation behaviour during solidification was analysed. The simulated results showed reasonable agreement with the as-cast microstructure observed experimentally.

The hot cracking behaviors of Mg-5Zn-xEr (x = 0.83, 1.25, 2.5, 5 wt.%) alloys are investigated by optimized hot cracking experimental apparatus, optical microscope, and scanning electron microscope, such as contraction behaviors, feeding behaviors, and permeability characteristics. It is found that the solid phase fraction at hot crack initiation and within the freezing range both increased with increasing Er contents up to 2.5 wt.% and then decreased at 5 wt.% Er content. The Mg-5Zn-5Er alloy exhibits the lowest solid phase fraction (87.4%) and a reduced freezing range (74.2 °C), which leads to more effective liquid feeding in the latter stages of solidification. Combined with the grain size, the permeability of the mushy zone, and fracture morphology, the overall permeability is optimal in the Mg-5Zn-5Er alloy, which is beneficial for feeding the cavities and micro-pores. Meanwhile, a large amount of W phase precipitated by the eutectic reaction (L→α-Mg + W phase), which facilitates healing of the incurred cracking. Conversely, the Mg-5Zn-2.5Er alloy shows inferior feeding ability due to the lowest solid phase fraction (98.3%), wide freezing range (199.5 °C), and lowest permeability. Therefore, the Mg-5Zn-2.5Er alloy exhibits maximal hot cracking susceptibility, and the Mg-5Zn-5Er alloy exhibits minimal hot cracking susceptibility. This work provides guidance for improving the hot cracking resistance of cast Mg-Zn-Er alloy and enables an understanding of the hot cracking behaviors of Mg-Zn-RE alloys. [ABSTRACT FROM AUTHOR]

The unique thermal cycle of selective laser melting (SLM) significantly affects the undesirable formability and mechanical properties of the deposited parts, especially for materials with complex compositions. Laser shock peening (LSP) is a strengthening technology that can refine grain, convert tensile stress to compressive stress, and improve fatigue strength. In situ LSP is a technology that combines LSP and SLM without ablative coating. The combination can strengthen the additive manufacturing microstructure layer by layer. Some literature has verified the feasibility of no absorption layer and pressure confining layer LSP. However, little research reported the effects of the in situ combination on the molten pool. In this work, the finite element method (FEM) has systematically investigated the impact of scanning speed and in situ LSP on fluid flow behavior, heat transfer, and the solidification process of the molten pool. The flow velocity and the size of the molten pool decrease as the scanning speed increases. The solidification rate shows an increasing-decreasing-increasing process at low scanning speed during the solidification process. Moreover, the value of R is consistently stable at high scanning speeds. The temperature gradient increases gradually and decreases sharply with the scanning speed increase. The in situ LSP reduces the temperature and the fluid flow of the molten pool, which decreases the heat convection and the value of Peclet number, but has little effect on the solidification process of the molten pool. [ABSTRACT FROM AUTHOR]

The techniques for releasing thermal energy accumulated in periods of high availability to meet the demand in periods of low energy supply contribute to the continuity of the cycles involved in thermodynamic processes. In this context, phase change materials are capable of absorbing and releasing large amounts of energy in relatively short periods of time and under specific operating conditions. However, phase change materials have low thermal conductivity and need to be coupled with high-thermal-conductivity materials so that the heat flux can be intensified and the energy absorption and release times can be controlled. This work aims to numerically study the solidification process of a phase change material inserted into a triplex tube heat exchanger with finned copper walls to intensify the thermal exchange between the phase change material and the cooling heat transfer fluid, water, that will receive the energy accumulated in the material. This work proposes the 3D numerical modeling of the triplex tube heat exchanger with finned walls and meets the need for numerical models that allow for the analysis of the full geometry of the latent heat thermal energy storage system and the thermal and fluid dynamic phenomena that are influenced by this geometry. Results of the temperature, liquid fractions and velocity fields during phase transformations are presented, analyzed and validated with experimental data, presenting average errors of below 5%. The total material discharge time was approximately 168 min, necessary for the complete solidification of the phase change material, with water injected into the triplex tube heat exchanger at a flow rate of 8.3 L/min and a temperature of 68 °C. The solidification process occurred more slowly in the same direction as the length of the triplex tube heat exchanger, and from 80% of the material in the solid state, the difference between the solidification time for z = 0 and z = 480 mm was 30 min. The fluid dynamic conditions developed in the latent heat thermal energy storage system promoted a maximum negative heat flux of −6423 w/m2 to the annular internal surface and −742 w/m2 to the annular external surface, representing a heat removal process nine times less intense on the external surface. The total energy released to the cooling heat transfer fluid was 239.56 kJ/kg. [ABSTRACT FROM AUTHOR]

The effect of Ca element on the microstructure evolution of the AZ91 magnesium alloy was investigated in this research. The magnesiumaluminium alloy AZ91 was inoculated with the Emgesal® Flux 5 to refine its microstructure and also improve its microstructure. Six different concentrations of the Emgesal® Flux 5 content were tested, ranging from 0.1 to 0.6% wt., and compared to the baseline of the AZ91 alloy without inoculation. Melted metal was poured into a preheated metallic mould. Samples to test were achieved after turning treatment. Formed microstructure was assessed using an optical microscope. The microstructure was refined for every tested samples. Mechanical properties such as tensile strength, elongation, Brinell hardness, Vickers microhardness, abrasion resistance and adhesive resistance were tested on the inoculated samples and compared to the non-inoculated AZ91. Introducing an Emgesal®Flux 5 inoculant caused a change in the tensile strength, elongation, Brinell hard-ness, Vickers microhardness, abrasive wear resistance as well as adhesive wear resistance in each examined concentration. [ABSTRACT FROM AUTHOR]

The paper focuses on the numerical modeling of the three-dimensional solidification process of steel using the finite element method (FEM). The model includes and discusses the formation of shrinkage cavities and the influence of the solid phase content on the feeding of the casting through the riser. The analysis assumed a critical value of the solid phase content, at which the transport of liquid phase from the riser to the casting is interrupted. The results of numerical simulation are presented to investigate the influence of this factor on the final quality of the casting. The model neglects the fluid motion in the liquid and solid-liquid regions and replaces the influence of the mold with appropriate boundary conditions. [ABSTRACT FROM AUTHOR]

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed.

The article concerns the experimental verification of the numerical model simulating the solidification and cooling processes proceeding in the domain of cast iron casting. The approximate course of the function describing the evolution of latent heat and the value of substitute specific heat resulting from its course were obtained using the thermal and derivative analysis (TDA) method The TDA was also used to measure the cooling curves at the distinguished points of the casting. The results obtained in this way were compared with the calculated cooling curves at the same points. At the stage of numerical computations, the explicit scheme of the finite difference method was applied. The agreement between the measured and calculated cooling curves is fully satisfactory.

In this work, latent heat thermal energy storage system composed of porous metal foams with phase change material subject to pulsating fluid flow is investigated. The pulsating admission of such systems has not been thoroughly studied so far. Thus, the main motivation of the present study has been the investigation of the effect of pulsating admission in comparison with the constant through flow. The investigation is carried out numerically, utilizing the thermal lattice Boltzmann method, adopting a dual distribution function approach for calculating the dynamic and thermal fields, within the framework of an in-house developed code. The porous media is modeled at a macroscopic level by the representative elementary volume scale approach, utilizing the Brinkman–Forchheimer extended Darcy model, without assuming thermal equilibrium between the fluid phase and the solid foam. The phase change is modeled by an enthalpy–porosity approach. The main novelty of the work resides in the analysis of pulsating flow effects on melting and solidification of a phase change material embedded in porous metal foam, as this has not been investigated that thoroughly before. Furthermore, in difference to the previous work, detailed energy and exergy analyses incorporating entropy generation rates are presented, making up a further important novel aspect of the present work. A parametric study is performed covering a range of the porosity (0.7, 0.8, 0.9). For pulsating flow, variations in the amplitude (0.1, 0.5, 0.9) and Strouhal number (0.1, 1.0) are investigated. The analysis of the pulsating flow shows that small pulsation amplitudes speed up the melting rate and the heat spread. The overall system irreversibility is observed to decrease with decreasing Strouhal number. The dependence of the system irreversibility on the pulsation amplitude has been observed, however, to be different between charging and discharging phases, which has been an interesting result. During charging, it is observed that low amplitudes lead to low irreversibility. However, high amplitudes are observed to be correlated with low irreversibility during discharging. By comparison with the previous work, the superiority of pulsating flow compared to the constant flow in picking up the maximum energy storage while minimizing thermal losses is demonstrated. Article Highlights: Numerical study of a pulsed flow's effects on the phase change within a porous channel. The pulsating flow is more useful than steady flow to pick up the maximum energy amount. Pulsating flow with a low Strouhal number and large pulsating amplitude is advised to mitigate the system's irreversibility during melting/solidifying process. [ABSTRACT FROM AUTHOR]

The size and distribution of TiN particles have a great influence on the properties of industrial pure iron. It is necessary to understand TiN precipitation behavior in bloom. Herein, inclusions in industrial pure iron cast billets are observed. The temperatures and conditions for TiN precipitation are calculated using thermodynamics and kinetics. The results show a large number of TiN inclusions in the bloom, and the quantity density is the largest at the inner arc of the bloom. This is caused by the large cooling rate at the inner arc and the homogeneous nucleation of inclusions. According to the thermodynamic calculations, during the solidification of industrial pure iron, TiN begins to precipitate at a solidification fraction greater than 0.82. The amount of TiN precipitated during solidification is 93%, with TiN continuing to precipitate from the solid phase after the solidification is complete. The results of TiN particle growth kinetics reveal that MgO is the most effective in promoting TiN nucleation, followed by δ‐Fe, CaS, and MgAl2O4, the effectiveness of Al2O3 as a heterogeneous nucleation core is relatively poor. The radius of the TiN particles decreases with a decrease in the N and Ti content and an increase in the cooling rate. [ABSTRACT FROM AUTHOR]

Abstract In a cylindrical shell and multi-tube heat exchanger (of large configuration), the incorporation of four distinct nanoparticles (Al2O3, MgO, SiO2, and SnO2) at various concentrations (0%–5%, v/v) into PCM (RT82) was investigated during the solidification process. A numerical model was developed and validated through experimental and theoretical findings found in literature. Whatever the metal oxides’ concentration, a clear enhancement of the freezing rate of PCM was observed over its solidification period, where this improvement was boosted proportionally with the rise of metal oxides concentration. However, the worst performance of the nano-PCM system was obtained using SnO2 nanoparticles, where a total solidification of PCM is observed after 26000 s for 5% (v/v) SnO2. In contrast, the best performance was resulted using SiO2, for which a total hardening of PCM was reached after 21000 s for 5% (v/v) silicon dioxide. This means that a reduction of 19.23% of the freezing period was obtained using SiO2 compared to SnO2 system at the same volume fraction (5%). It was found that in presence of nanoparticles (nano-PCM system), the solidification rate of PCM is in the order: SiO2>MgO > Al2O3>SnO2. According to the thermo-physical properties of metal oxides, it was found that the enhancing role of nanoparticles (toward PCM solidification) is density-dependent. Therefore, the effect of heat capacity may be overlooked. [ABSTRACT FROM AUTHOR]

Experiments were carried out to determine the effect of cooling rate on the nucleation, growth and microstructure evolution during the solidification process in Ce containing S31254 high Mo austenite stainless steel (HMASS). In situ observations and in situ quenching tests indicate that the Ce effects in this steel are to refine the equiaxed grain and change in the secondary phase from σ to δ, but are mainly suitable for the medium and low cooling rate. The high cooling rate is highly beneficial for austenite nucleation and significantly influence the primary austenite grain growth behavior. The growth velocity for austenite grain is increased with the increase in cooling rate. The morphology of the primary austenite would change from a crescent shape to rod shape with the cooling rate increased from 50 °C/min to 100 °C/min. Rod-shaped grains with high nucleation densities would make primary grains easy to be combined together, which would reduce the ability of the refined grain. Furthermore, a high cooling rate could slightly improve the solute redistribution, while it significantly deteriorated the micro-segregation of Mo in a solidified structure. The main reason is that high cooling rate could worsen the kinetic condition of ferrite precipitation and postpone the precipitation reaction at the end of the solidification process. [ABSTRACT FROM AUTHOR]

A laser vibrometer system in combination with appropriate artificial intelligence methods for clustering of the measured vibration spectra was tested at a continuous steel casting machine to receive information on the solidification status of the strand. Measurements with the laser vibrometer at a fixed strand position of the billet caster of ESF under conditions of incrementally increasing casting speeds revealed a transition in the population of the identified vibration clusters as a footprint of the passed crater end position with a change from a fully solidified strand to a strand with some liquid core at the measurement position. This was in accordance with the results from a three-dimensional dynamic temperature and solidification model which was set up based on a state-of-the-art approach for solution of the heat flow equation with tailored submodels for the different boundary zones of the ESF billet caster (i.e., mould, secondary spray water zones and radiation zones) and installed at the steel plant for online monitoring and control of the casting process. The application of the newly installed measurement and model-based information systems at ESF revealed significant improvements in their billet casting process in terms of halved strand breakout rates and correspondingly increased productivity. [ABSTRACT FROM AUTHOR]

Due to the structural inheritance, a uniform and refined as-cast microstructure is usually desirable for further thermomechanical processing of biodegradable Zn alloys. Considering the effectiveness of pulsed magnetic field (PMF) for structure refinement and homogenization, a high-voltage PMF was applied to the solidification process of Zn-Cu alloys with different compositions in this work. For Zn-1.5Cu alloy, a 6 kV PMF (i.e., a PMF generated by a discharge voltage of 6 kV) transformed the macrostructure from a mixture of coarse columnar and equiaxed η-Zn grains with an average size of 1437 ± 482 μm to homogeneously distributed fine equiaxed η-Zn grains with an average size of 454 ± 15 μm. For Zn-2.5Cu alloy, a 6 kV PMF changed the long dendritic primary ɛ-CuZn4 particles into fine dot-like particles. Correspondingly, the coarse equiaxed η-Zn grains with an average size of 1895 ± 375 μm are transformed to fine equiaxed ones with an average size of 446 ± 46 μm due to the increase in amount of the primary ɛ-CuZn4 particles as potent heterogeneous nucleation sites. For Zn-4.0Cu alloy, a 6 kV PMF causes segregation of the primary ɛ-CuZn4 particles at the lower part of the specimen and intensifies the macrostructural inhomogeneity. For all the alloys, the most significant effect of the PMF on structure refinement and homogenization occurs in the early stage of solidification. The convection and Joule heat induced by the PMF in the melt are responsible for the structural transformation. [ABSTRACT FROM AUTHOR]

The real-time observation of molten materials and their cooling to solid state is of importance for many industrial processes. In this work, we describe additional possibilities obtained by the implementation of a Rapid Scan technique on an FT-IR emissometer designed to allow the observation of materials under extreme temperature conditions. The possibility of following liquid-to-solid state phase transition mechanisms through time-resolved emissivity will be illustrated. This new methodology presents interesting possibilities for the study of structural transformations through the real-time monitoring of the dielectric function and true sample temperature of the experimental emissivity spectra acquired every 50 ms under free cooling conditions.

The phase change thermal storage technology has broad application prospects in the field of solar thermal power generation and the fins can effectively increase the charge and release rate of the phase change heat storage. However, the dynamic nonlinear characteristics of phase change heat storage seriously restrict the optimization of fin structures. Therefore, this paper proposed a fast optimization algorithm for optimizing the fin structure of the phase change heat storage. The algorithm takes the shortest distance from the phase change material to the fin and the cold source as the optimization objective, and uses the genetic algorithm to optimize the structure of fin. This method solves the time-consuming problem of traditional numerical optimization methods. The one-level Y-shaped fin in a shell and tube phase change heat storage was taken as an example. Under the premise of meeting a certain amount of fin material, the width ratio and length of each branch and the angle between branches of Y-shaped fin were selected as the design variables, and the influence of the number of fins was analyzed. The results show that the optimization objective proposed in this paper is feasible, and the optimized fin structure presents an arrow shape. Under the heat release conditions studied in this paper, compared with the traditional Y-shaped fins, the optimized fin structure can shorten the complete solidification time by 41.3%-62.1% when the number of fins is 1-3.

The magnesium–aluminium alloy AZ91 was inoculated with zirconium to refine the microstructure. Six different concentrations of zirconium content were tested, ranging from 0.1 to 0.6 wt %, and compared to the baseline AZ91 alloy without modification. Melted metal was poured into a preheated ceramic mould and the temperature was measured and recorded during the solidification. The derivative and thermal analysis (DTA) was performed to compare the crystallisation dynamics. Formed microstructure was analysed using an optical microscope, scanning electron microscopy (SEM-EDX) and energy dispersive X-ray spectrometry (XRD). The chemical composition was measured using an arc spectrometer. The time of solidification was shortened for the samples with a concentration of zirconium 0.3 wt % and the microstructure was refined. The level of grain refinement remained below 10% and the grain shape was changed to more spherical shapes. Both the primary magnesium and eutectic phases were modified. However, at a low concentration of zirconium (0.1 and 0.2 wt %), the primary grain size was increased. Therefore, the optimal zirconium concentration was 0.3 wt %. Larger concentrations (0.4 to 0.6 wt %) did not provide any additional benefit. Theoretical analysis showed that some Al3Zr intermetallic phases can form, which was confirmed on the derivate curve of the thermal analysis, and SEM-EDS and XRD analyses. [ABSTRACT FROM AUTHOR]

Unidirectional freeze casting followed by sintering and infiltration treatments has been proved to be a promising method to produce lamellar composites with good strength and toughness. However, it remains a great challenge to tailor the microstructure, particularly the lamellar orientation at the centimeter scale and the architectural features over multiple scales. Herein, we prepared Al/(Al 2 O 3 –TiC) composites with a long-range ordered lamellar architecture via bidirectional freeze-casting and melt-infiltration techniques. The incorporation of a certain amount of TiC (∼3 μm in diameter) into the Al 2 O 3 slurry increased the solidification velocity and decreased the ceramic layer thickness. Furthermore, it greatly facilitated the infiltration of liquid Al into the interlamellar channels and in-layer cavities, thus improving the mechanical properties of the composites. The maximum flexural strength (474 ± 8 MPa) and crack-growth toughness (42.7 ± 2.7 MPa m1/2) appeared in the composite containing ∼27 vol% ceramics with Al 2 O 3 :TiC = 5:5. Moreover, the composites exhibited anisotropic mechanical properties. The flexural strength loaded in the direction parallel to the ceramic layers was higher than that perpendicular to them, while the toughness exhibited an opposite trend. The main toughening mechanisms included crack blunting, crack deflection, plastic deformation of the metal layers and multiple cracking. This work offers a cost-effective and scalable method for the fabrication of laminated composites with exceptional damage tolerance. [Display omitted] • A new strategy is proposed to construct 3D-aligned lamellar hierarchical structure. • The presence of TiC facilitates the infiltration of Al into the ceramic lamellae. • Increasing TiC:Al 2 O 3 ratio reduces layer thickness and promotes multiple cracking. • Enhanced strength and toughness stem from the optimized structure and composition. [ABSTRACT FROM AUTHOR]

Modification of the eutectic silicon in Al–Si alloys causes a structural transformation of the silicon phase from a needle-like to a fine fibrous morphology and is carried out extensively in the industry to improve mechanical properties of the alloys. The theories and mechanisms explaining the eutectic modification in Al–Si alloys are considered. We discuss the mechanism of eutectic rubidium modification in the light of experimental data obtained via quantitative X-ray spectral microanalysis and thermal analysis. X-ray mapping revealed that rubidium, which theoretically satisfies the adsorption mechanisms of silicon modification, had an effect on the silicon growth during solidification. Rubidium was distributed relatively homogeneously in the silicon phase. Microstructural studies have shown that rubidium effectively refines eutectic silicon, changing its morphology. Modification with rubidium extends the solidification range due to a decrease in the solidus temperature. The highest level of mechanical properties of the alloy under study was obtained with rubidium content in the range of 0.007–0.01%. We concluded that rubidium may be used as a modifier in Al-Si eutectic and pre-eutectic alloys. The duration of the modifying effect of rubidium in the Al-12wt%Si alloy melt and porosity in the alloy modified with rubidium were evaluated.

A high-vanadium alloy composite layer was prepared on the surface of a carbon steel using cast composite technology, and the wear properties of the composite layer were investigated. The results showed that the microstructure of the composite layer was composed of primary vanadium carbides (VC), flake martensite, residual austenite, and fine VC. The hardness of the cast alloy layer was 63 HRC. The abrasive wear resistance and impact wear resistance were increased by 60% and 26%, respectively, compared with those of high-chromium cast iron. The excellent wear resistance of the cast alloy layer is attributed to the high-hardness primary vanadium carbide and the large number of fine secondary vanadium carbides precipitated out of the cast alloy layer. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the solidification process of the phase change material (PCM) in the shell‐and‐tube latent‐heat thermal energy storage unit (LTESU) strengthened by fin is studied. For improving the strengthening effect of fins on the solidification performance of shell‐and‐tube LTESU, this paper proposes a novel connected‐Y‐shaped fin. The novel fin is inspired by the interconnection of the internal texture of the lotus leaf, and the branches of the two‐level Y‐shaped fins are connected into a whole by three metal annuluses. The numerical simulation method is applied to investigate the influence of the connected‐Y‐shaped fin on the solidification performance of PCM. The effects of annulus position and fin width on solidification performance are studied and analyzed. At the same time, the effects of the connected‐Y‐shaped fin on the solidification process under different wall temperatures and the radius ratio of outer to inner tube (γi) are investigated. The results indicated that the connected‐Y‐shaped fin can significantly enhance the discharging performance of LTESU. Compared with the traditional two‐level Y‐shaped fins, the optimized connected‐Y‐shaped fin can shorten the PCM solidification time by 53.9%. The optimum width ratio of the connected‐Y‐shaped fin should be 2. The optimum radius ratio of the outer annulus, middle annulus, and inner annulus to the outer tube should be 0.91, 0.64, and 0.41, respectively. The scope of application of the conclusion is that Ste = 0.139 − 0.496, and γi = 0.083 − 0.167. Highlight: A novel connected‐Y‐shaped fin is proposed for the latent heat storage unit.The influences of fin structure parameters on the solidification process are discussed.Optimum fin parameters are recommended for maximizing the solidification rate.The novel fin can decrease the solidification time of PCM by 53.9%. [ABSTRACT FROM AUTHOR]

Hot tearing is one of the most serious defects during the casting solidification process. In this study, a new type of multichannel "cross" hot tearing device was designed. The hot cracks initiation and propagation were predicted by the relationship between temperature, shrinkage force and solidification time during the casting solidification process. The reliability and practicability of the multichannel "cross" hot tearing device were verified by casting experiments and numerical simulations. The theoretical calculation based on Clyne-Davies model and numerical simulation results show that the hot tearing tendency decreases in the order: 2024 Al alloy>Al-Cu alloy>Al-Si alloy at a pouring temperature of 670 °C and a mold temperature of 25 °C. Feeding of liquid films at the end of solidification plays an important role in the propagation process of hot tearing. The decrease of hot tearing tendency is attributed to the feeding of liquid film and intergranular bridging. [ABSTRACT FROM AUTHOR]

The article concerns the experimental verification of the numerical model simulating the solidification and cooling processes proceeding in the domain of cast iron casting. The approximate course of the function describing the evolution of latent heat and the value of substitute specific heat resulting from its course were obtained using the thermal and derivative analysis (TDA) method The TDA was also used to measure the cooling curves at the distinguished points of the casting. The results obtained in this way were compared with the calculated cooling curves at the same points. At the stage of numerical computations, the explicit scheme of the finite difference method was applied. The agreement between the measured and calculated cooling curves is fully satisfactory. [ABSTRACT FROM AUTHOR]

An in-situ real-time study on solid phase formation and its degree of structural disorder could shed light on the mechanisms of solidification from the liquid and allow insight into the creation of materials designed to possess enhanced properties and facilitate their production and application. The implementation of a Rapid Scan technique on a FT-IR emissometer designed to allow the observation of materials under extreme temperature conditions allows following the liquid to solid-state phase transition mechanisms through time-resolved emissivity spectra acquired at a speed of 20 spectra per second. The cooling rate of the material can be modified by controlling the laser-heating system. This technique has been validated on SrAl 2 Si 2 O 8 feldspar, a material which displays structural disorder. The technique is sufficiently accurate to determine small changes in the linewidths of spectra obtained at different cooling rates, suggesting that structural order is increased at slower cooling speeds and confirming the Al/Si ordering dependence on thermal history. [ABSTRACT FROM AUTHOR]

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys. [ABSTRACT FROM AUTHOR]

The effect of additional ultrasonic treatment (AUT) on grain refinement and distribution of the SiC particles in brazing seam at different temperatures during the solidification process of brazed joints was investigated, and the mechanism model was constructed. The reason for the microstructural changes induced by AUT was explained. The experimental results indicated that the AUT could effectively refine grain, promote element diffusion, and improve the macroscopic uniformity of SiC particles. Further, the effect of AUT was different at different temperatures. At 480 °C, the power ultrasound promoted the SiC particles migration and grain nucleation. In the semi-solid temperature range, the ultrasonic cavitation played a leading role in help α-Al growing to equiaxed grains. In solid-state, ultrasound only played a role in promoting elements diffusion. When the temperature was 420 °C, the ultrasound effect is best that the average grain size of α-Al is 14.6 μm, the joint's shear strength is 196.5 MPa. [ABSTRACT FROM AUTHOR]

To tackle global warming, a reliable storage system seems crucial due to unpredictability of renewable energy. As a result, storage units based on Phase Change Material (PCM) are found to be of great worth where latent heat transfer occurring in an almost isothermal condition lay the foundation for far more compact and easy-to-fabricate storage components. Despite their advantageous, one major drawback being weak thermal conductivity needs to be addressed. So, in this study a triplex-tube heat exchanger with tree-like and rectangular fins along with hybrid nanoparticles made of MoS2-TiO2 are put into perspective to dispose of this weakness and Galerkin Finite Element Method (GFEM) is applied using FlexPDE to analyze the solidification process and evaluate the influence of single and combined usage of fins and nanoparticles. Moreover, the credibility of this study and GFEM has been confirmed by an experimental work. The results unveiled that, while the combined usage of nanoparticles and tree-like fins gives the best result by lowering the solidification time by 78% compared to bare tube, tree-like fins claim the best performance taking 1700 s followed by rectangular fins with 3500 s if nanoparticles are out of reach.

This paper presents results of a study of the effect of inoculation of yttrium on the microstructure of AZ91 alloy. The concentration of the inoculant was increased in samples in the range from 0.1% up to 0.6%. The influence of Y on the thermal effects resulting from the phase transformations occurring during the crystallisation at different inoculant concentrations were examined with the use of Derivative and Thermal Analysis (DTA). The microstructures of the samples were examined with the use of an optical microscope; and an image analysis with a statistical analysis were also carried out. Those analyses aimed at examining oh the effect of inoculation of the Y on the differences between the grain diameters of phase αMg and eutectic αMg + γ(Mg17Al12) in the prepared examined material as well as the average size of each type of grain by way of measuring their perimeters.

The techniques for releasing thermal energy accumulated in periods of high availability to meet the demand in periods of low energy supply contribute to the continuity of the cycles involved in thermodynamic processes. In this context, phase change materials are capable of absorbing and releasing large amounts of energy in relatively short periods of time and under specific operating conditions. However, phase change materials have low thermal conductivity and need to be coupled with high-thermal-conductivity materials so that the heat flux can be intensified and the energy absorption and release times can be controlled. This work aims to numerically study the solidification process of a phase change material inserted into a triplex tube heat exchanger with finned copper walls to intensify the thermal exchange between the phase change material and the cooling heat transfer fluid, water, that will receive the energy accumulated in the material. This work proposes the 3D numerical modeling of the triplex tube heat exchanger with finned walls and meets the need for numerical models that allow for the analysis of the full geometry of the latent heat thermal energy storage system and the thermal and fluid dynamic phenomena that are influenced by this geometry. Results of the temperature, liquid fractions and velocity fields during phase transformations are presented, analyzed and validated with experimental data, presenting average errors of below 5%. The total material discharge time was approximately 168 min, necessary for the complete solidification of the phase change material, with water injected into the triplex tube heat exchanger at a flow rate of 8.3 L/min and a temperature of 68 °C. The solidification process occurred more slowly in the same direction as the length of the triplex tube heat exchanger, and from 80% of the material in the solid state, the difference between the solidification time for z = 0 and z = 480 mm was 30 min. The fluid dynamic conditions developed in the latent heat thermal energy storage system promoted a maximum negative heat flux of −6423 w/m2 to the annular internal surface and −742 w/m2 to the annular external surface, representing a heat removal process nine times less intense on the external surface. The total energy released to the cooling heat transfer fluid was 239.56 kJ/kg.