Solidification Period Research Articles

Insight into Role of Arc Torch Angle on Wire Arc Additive Manufacturing Characteristics of ZL205A Aluminum Alloy.

The arc torch angle greatly affected the deposition characteristics in the wire arc additive manufacturing (WAAM) process, and the relation between the droplet transition behavior and macrostructure morphology was unclear. This work researched the effect of torch angle on the formation accuracy, droplet transition behavior and the mechanical properties in the WAAM process on a ZL205A aluminum alloy. The results suggested that at the obtuse torch angle, part of the energy input was used to heat the existing molten pool, which was optimized for the longer solidification period of the molten pool. Therefore, the greater layer penetration depth at 100° resulted in the improved layer-by-layer combination ability. The obtuse torch angle was associated with the better formation accuracy on the sidewall surface due to the smaller impact on the molten pool, which was influenced by both the arc pressure and droplet impact force. The eliminated pores were optimized for the mechanical properties of depositions at a torch angle of 100°; thus, the tensile strength and elongation attained maximum values of 258.6 MPa and 17.1%, respectively. These aspects made WAAM an attractive mode for manufacturing large structural components on ZL205A aluminum alloy.

Computational Investigation of the Influencing Parameters on the Solidification of Thermoplastic Beryllium Oxide Slurry in a Cylindrical Shell

This article presents a computational study of the influencing parameters on the solidification of the thermoplastic beryllium oxide slurry in an annular forming cavity. The main purpose of this paper is to study the effect of cooling and casting conditions on the solidification of the BeO suspension by considering the temperature-dependent rheological and physical properties. The results of calculations of the Bingham–Papanastasiou rheological model with experimental data in the intervals of phase transitions with different casting rates of beryllium ceramics have been validated. The use of the regularization parameter made it possible to approximate the flow of the slurry at all levels of its shear rates as highly viscous, followed by a continuous transition to a solid state. The speed of heat removal from the molding during the solidification period is determined by the speed of movement of the slurry and the temperature field on which the width of the transition region depends. The process of solidification of the slurry mass has been evaluated by changing its heat flow distribution and density along the length of the concentric channel. The obtained model calculation results make it possible to control the casting process and eventually realize a uniform structure of castings.

Evaluation of influence of thermoplastic slurry flow conditions on heat transfer coefficient during beryllium ceramic formation

The article presents the results of calculation of the influence of thermoplastic slurry flow conditions on the total heat transfer coefficient when forming ceramic products. Methods of detailed description of casting processes and thermal calculations have been developed to ensure reliable correspondence of calculated data and experimental results implemented on the basis of calculational experiment. The modeling of physical processes occurring during the formation of products allows you to discover new opportunities for improving the quality of castings by allowing you to more closely track the change in the temperature-phase fields of the process and clearly present the solidification kinetics depending on the casting modes. The speed of heat removal from the casting during the solidification period determines the rate of movement of the slurry, along with the temperature field on which the width of the transition region depends. These factors have a direct influence on the formation of the structure of beryllium ceramics. The study of the heat exchange process in the formation of ceramic products depending on temperature, heat at phase transition is the main task, since they largely determine the technological and operational characteristics of beryllium ceramics. The design data allows to determine the optimal conditions of the ceramic casting process and to obtain a solidified product with a uniform structure at the outlet.

Experimental study and neural network model based prediction of layer thickness influence on LPBF IN625 single track geometry

The performance of interacting metal surfaces having sliding motion is enhanced by fabricating microfeatures on-top of the surfaces. Laser powder bed fusion (LPBF) is used to fabricate the microfeatures of IN625 on-top of a flat surface. In LPBF, geometrical characteristics of microfeatures are based on the energy supplied and the volume of material melted (layer thickness) at that instant of time. There is very few research reported in open literature on the effect of layer thickness on microfeatures geometry during LPBF. In this work, a series of single tracks is fabricated with different combinations of laser power and scanning speed for 75 μm, 100 μm, and 125 μm layer thickness and its effect on single track geometrical characteristics and microstructure was evaluated. It has been found that laser power and scanning speed have a significant influence on the track geometry irrespective of layer thickness. The minimum linear energy density of 2.5 J/mm is considered to fabricate the continuous track formation for investigated layer thickness. From statistical analysis, it is observed that the laser power and scanning speed shows higher contribution on track width and remelting depth, respectively. Whereas, layer thickness shows a higher influence on track height and contact angle of single track as compared to laser power and scanning speed. In 125 μm layer thickness, the volume of material melting is increased which encourages the gravity effect to deform the melt pool and produces larger track width compare to 100 μm layer thickness. Further, the cell spacing is gradually increased with layer thickness resulting increase in the solidification period. The shape controllability of the single track is significantly increased with layer thickness, but as keeps on increasing layer thickness due to the larger volume of molten metal, the melt pool losses ability to maintain convex shapes. An Artificial Neural Network (ANN) model is developed to understand the relationship between the LPBF process parameters and single track geometrical characteristics to predict the responses for a wide range of process parameters. The multiple response neural network model shows excellent agreement with experimental results with R2 value greater than 0.95.

Exploring the impact of inner and middle channel geometries on the melting rate of PCM-metal foam composition in a triplex tube heat exchanger

Triplex tube heat exchangers (TTHXs) are devices suitable for storing thermal energy with PCM because they shorten the melting and solidification periods. Studies in literature have revealed that pipe geometries significantly affect the melting performance of PCM in thermal energy storage with TTHX. In the pipe designs carried out in these studies, convection in the heat transfer fluid (HTF) and the heat transfer surface areas of the pipes were considered. However, in addition to convection in the HTF, heat transfer by conduction and convection within the PCM also significantly affects the melting performance. The novelty of this study was to investigate the effects of inner and middle channel combinations with different geometries in TTHX on conduction and natural convection mechanisms in PCM combined with metal foam. Numerical analyses were carried out for nine inner-middle channel combinations with three different metal foam porosity values (ε = 0.85, 0.90 and 0.95). At porosity values of 0.85 and 0.90, the highest melting rate was achieved with the triangle-triangle inner-middle channel combination within a certain period, and the charging time was shortened by 16.67 % and 14.44 %, respectively, compared to the base case (circle-circle). For the porosity value of 0.95, it was observed that the most suitable channel combination for melting performance was circle-circle, as natural convection flow became more dominant in heat transfer in liquid PCM. At the porosity value of 0.95, the charging time with TTHX containing the circle-circle combination decreased by values ​​ranging from 29.75 % to 59.86 % compared to other combinations.

Management of period of solidification with loading nanoparticles simulating unsteady heat transfer

This article explores the acceleration of discharge speed through the introduction of nanoparticles. Utilizing simulations based on the Galerkin method, the study has developed and examined the effects of various variables. The utilized tank has been equipped with fin and additives with various shape factor (m) and volume fraction (φ) have been dispersed into water. The denser mesh near the ice front was considered in each time stage involving adaptive grid approach. Also, a validation test was presented to illustrate the precision of modeling. Contours and curves for different ranges of parameters were exemplified in results. The quickest process takes 641.19s while the longest process takes 877.17s. Increasing m causes conductivity to increase and speed of process enhances about 6.96 %. Moreover, augmenting the value of φ makes period of process reduce about 26.9 %.

Thermal characteristics of metal foams proportion on heat transfer enhancement in the melting and solidification process of phase change materials

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.

Evaluation of the different inner and outer channel geometry combinations for optimum melting and solidification performance in double pipe energy storage with phase change material: A numerical study

Phase change materials (PCMs) have become preferable among latent heat storage methods due to their high energy storage densities and low energy losses. These properties of PCMs make it possible to use them in applications such as thermal storage of solar energy, cooling of electronic equipment, energy storage for buildings, and cooling of engines. Double-pipe energy storage (DPTES) with PCM can be used in cases where the production and consumption times of the thermal energy obtained from sources such as solar energy, geothermal water, and waste gas do not match. The fact that the thermal conductivity coefficients are quite low is one of the obstacles to the commercialization of PCMs and their use in more applications. Double-pipe energy storage (DPTES) with PCM can be used especially in cases where the production and consumption moments of the thermal energy obtained from solar energy do not match. In studies on DPTES with PCM, methods including different pipe geometries, extended surfaces, different PCM materials, microencapsulation of PCMs, eccentric inner pipe placement, nanoparticle usage, and metal foam addition have been investigated to increase thermal conductivity. The novelty of this study was to examine the effects of different inner and outer channel combinations on melting and solidification performance. In this direction, nine different inner and outer channel combinations of basic geometric shapes were modeled. Among these combinations, the combination with the highest melting rate and the shortest charging time was determined. Afterward, melting and solidification analyzes were made at the different positions of the inner and outer channels for the combination selected, and the most suitable energy storage design was created to make the most efficient use of the existing heat source. The results of the analysis revealed that the optimum design for melting, and solidification performance was the triangle-in-square configuration. With this configuration, it was increased the melting rate by 1.1 times and accelerated the charging time by 20 % for a 40-minute charging period compared to conventional DPTES (circle-in-circle). In addition, for the melting and solidification periods, the inverted and vertical placement of the triangle in the square revealed the best results. It was observed that the effect of the relative positions of the square and the triangle on the solidification rate was negligible. It is predicted that the results given in this study will be useful in designing the most compatible inner and outer channel geometries to increase energy storage efficiency in DPTES systems.

Lunar Procellarum KREEP Terrane (PKT) Stratigraphy and Structure with Depth: Evidence for Significantly Decreased Th Concentrations and Thermal Evolution Consequences

Dating from the lunar magma ocean solidification period, the Procellarum KREEP Terrane (PKT) occupies 16% of the surface but has a much higher thorium abundance compared to the rest of the Moon and is thus interpreted to carry 40% of the radioactive elements by volume in the form of an anomalously thick KREEP-rich layer. Subsequent research has focused on the processes responsible for PKT concentration and localization (e.g., degree-1 convection, farside impact basin effects, etc.), and the effect of PKT high-radioactivity localization on lunar thermal evolution (e.g., topography relaxation, mantle heating, late-stage mare basalt generation, etc.). Here we use a stratigraphic approach and new crustal thickness data to probe the nature of the PKT with depth. We find that most PKT characteristics can be explained by sequential impact cratering events that excavated and redistributed to the surface/near-surface a much thinner Th-rich KREEP layer at depth, implying that no anomalous conditions of PKT thickness, radioactive abundances, geodynamics, thermal effects or magma generation are likely to be required as in the previous studies.

Enhanced thermal performance of the solidification process of nanopowder-phase change material-based latent thermal unit: Heat management

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.

"MODELING OF A CONTINUOUSLY CAST BILLET CENTRAL POROSITY REDUCING PROCESSES"

"The results of studies aimed at solving the actual problem of improving the quality of continuously cast billets are presented. Technical solutions have been developed to improve the crystallization process by means of pulsating metal blowing with an inert gas in the mold and shear reduction of the billet in the secondary cooling zone of a continuous casting machine (CCM). Physical modeling of shear reduction of continuously cast billets in the secondary cooling zone of CCM on model ingots has been carried out. The resulting macrostructures of model ingots were studied, indicating the absence of internal cracks in the central zone of the billet at a degree of deformation of up to 5 % and small shear angles (≤ 15–18°), and at a degree of deformation of more than 5 % and shear angles of about 18°, cracks develop periodically, emerging on the surface of the ingot. With pulsating blowing and shear «soft» compression in the final period of solidification, their positive effect on reducing the zone of columnar crystals and reducing the central porosity was established. Keywords: continuously cast billet, central porosity, CCM, crystallization, crack. "

Multi-objective optimization of various type finned heat sink with phase change materials (PCM)

The paper focuses on optimizing hybrid PCM filled heat sinks with a multi-objective approach. In the current study, the fins are oriented both horizontally at the sidewalls and vertically at the bottom side in the enclosure. Two heat sinks with different types of fin shapes are introduced in the enclosure. A rectangular shape finned heat sink, and a tapered shape finned heat sink is incorporated in both sidewalls and bottom walls. The study’s main goal is to optimize the PCM-based heat sink to prolong the charging cycle (melting) and shorten the discharging cycle (solidification). The PCM used in the study is n-eicosane, and the material for the heat sink is aluminum. A heat flux with constant supply of 2000 W/m2 is provided at the enclosure bottom, and the remaining walls are insulated. A 2-D numerical simulation is done using the commercial software ANSYS Fluent. The multi-objective optimization is carried out using the technique for order preference by similarity to ideal solution (TOPSIS) optimization technique. For a constant PCM volume for both the cases, fin spacing, fin positioning, and fin heights are varied. The output results determined the optimum configuration for the stretched melting period and minimized solidification period.

Application of physical simulation to evaluate the impact of teeming method and rate on axial zone formation of large ingots

The article presents the results of evaluation of the impact of teeming method and rate on solidification and formation of the axial zone of large ingots. The research is based on a physical simulation. With this aim a laboratory-scale plant (a crystallization mould) was designed and built which enabled to visualize and monitor solidification and structural formation of the model ingots. Sodium thiosulphate (crystal hyposulphite) – Na2S2O3·5H2O was used as a modeling solution. Matching of the processes in the model and in real industrial conditions of ingot teeming was assessed with similarity criteria obtained on the basis of the dimension theory with consideration of the physical and chemical processes in the ingot during its teeming and crystallization. Two methods – downhill casting and uphill casting – were used to teem the melt into the mould. During teeming the geometry and technological parameters of the model ingots remained unchanged while the teeming rate was altered. Length and medium width of the model ingot axial zone were measured. The thermal profiling of the surface of the mould model was monitored over the entire period of solidification to evaluate the thermal field alteration while the ingot was teemed and crystallized. Thermal imaging processing made it possible to observe temperature changes of the surface of the model mould from top to bottom for downhill cast ingots teemed at different rates. The results obtained demonstrate that teeming rate has a noticeable impact on the axial zone length. It was established that a decreased rate leads to an increased directionality of crystallization and improvement of the ingot axial zone structure.

Noninvasive tracking of solidification using ultrasound

Noninvasive tracking of solidification is typically done by monitoring the sample’s surface temperature. This approach is error-prone and not always appropriate for complex geometries and often does not provide complete information on the sample’s transitioning phases. This feasibility study investigates using ultrasonic waves to noninvasively track solidification in wax. Ultrasonic sensors are used in through-transmission mode to monitor the response over the solidification period. The difference in speed of sound between the wax’s liquid and solid phase allows for the solid fraction of the sample to be calculated over the solidification period and the time of complete solidification to be identified. Changes in attenuation during solidification are consistent across experiments. These changes are likely to provide additional information about the cast once they are fully understood. Temperature probes are used to verify the results obtained from the ultrasonic data. The ultimate goal of the project is to use a metal sample and connect information from the ultrasonic signal to the material properties and grain structure of the cast using noninvasive ultrasound technology.

Exploration of proper heating protocol for injectable horizontal platelet-rich fibrin gel

PurposePlatelet-rich fibrin (PRF) has been proposed as promising biomaterials with the advantages of host accumulation of platelets and leukocytes with entrapment of growth factors and fibrin scaffold. However, limitations including fast resorption rate (~ 2 weeks) restricts its clinical application. Recent studies have demonstrated heating treatment can prolong PRF degradation. Current published articles used the method of 75 °C for 10 min to obtain longer degradation, while few studies investigated the most suitable temperature for heating horizontal PRF. Our present study was to discover and confirm the optimum temperature for heat treatment before obtaining H-PRF gels by investigating their structure, mechanical properties, and bioactivity of the H-PRF gels after heating treatment.MethodsIn the present study, 2-mL upper layer of horizontal PRF was collected and heated at 45 °C, 60 °C, 75 °C, and 90 °C to heat 2-mL upper layer of horizontal PRF for 10 min before mixing with the 2-mL lower layer horizontal PRF. The weight, solidification time and the degradation properties were subsequently recorded. Scanning electron microscopy (SEM) and rheologic tests were carried out to investigate the microstructure and rheologic properties of each H-PRF gel. The biological activity of each H-PRF gel was also evaluated using live/dead staining.ResultsH-PRF gel prepared at 75 °C for 10 min had the fast solidification period (over a tenfold increase than control) as well as the best resistance to degradation. The number of living cells in H-PRF gel is greater than 90%. SEM showed that H-PRF gel becomes denser as the heating temperature increases, and rheologic tests also revealed that the heat treatment improved the mechanical properties of H-PRF gels when compared to non-heated control group. Future clinical studies are needed to further support the clinical application of H-PRF gels in tissue regeneration procedures.ConclusionsOur results demonstrated that the H-PRF gel obtained at 75 °C for 10 min could produce a uniform, moldable gel with a short time for solidification time, great rheologic behavior and, high percent of live cells in PRF gel. A promising use of the commonly utilized PRF gel was achieved facilitating tissue regeneration and preventing degradation.

Laser remelting of AlSi10Mg(-Ni) alloy surfaces: influence of Ni content and cooling rate on the microstructure

AlSi10Mg alloys are widely employed in a variety of industries, including aerospace, automotive, and microelectronics. This is because of its low density, acceptable mechanical properties, acceptable corrosion resistance, and inexpensive application cost. Advantageous fluidity, a short solidification period, and minimal volumetric contraction are beneficial characteristics under processing such alloys. Despite being used as commercial alloys, the mechanical properties of the AlSi10Mg alloys still need to be improved. In line with this, the current focus of Al-based alloy development is mostly on modifying commercially available alloys. Under such context, Ni was used as an alloying element in this study to generate the Al3Ni intermetallics, distinguished by its improved mechanical strength. Furthermore, the thermal stability of the Al3Ni may be a benefit, particularly for high-temperature applications. The present study aims to investigate the solidification under low and high cooling rates of four alloys: AlSi10Mg, AlSi10Mg-1Ni, AlSi10Mg-2Ni, and AlSi10Mg-3Ni (wt.%). Samples were obtained by directional solidification (DS) and laser surface remelting (LSR) processes. The cooling rates were calculated for the DS samples and with extrapolation for LSR samples as well as with the use of a model from the literature. After testing several laser conditions, the results also include an examination of microstructural and hardness changes in the treated and untreated zones. The produced gradient of microstructures is fully characterized as well as used to evaluate cooling rates inside the laser molten pools. For energy densities of 400 J/mm2 and 100 J/mm2, the mean dendritic spacings, λ, of the three Ni-containing alloys at the laser molten pool yielded estimated cooling rates of approximately 1.5 × 104 °C/s and 4.7 × 104 °C/s, respectively. A model explaining the reversion of λ across the molten pool will be outlined.

On/off directional solidification of near peritectic TRIS-NPG with a planar but tilted solid/liquid interface under microgravity conditions

Understanding phenomena that occur during gradient annealing and initial transient of Bridgman-type directional solidification processes is essential for producing high-performance materials with specific properties. An experiment with alternating long time gradient annealing and directional solidification periods was performed on the International Space Station, using a near-peritectic transparent TRIS-NPG alloy. It transpired that accumulation of solute ahead of the solid/liquid interface continued to progress and that steady-state growth conditions were never achieved. The results demonstrate that (i) liquid being squeezed out from the mush during the long time gradient annealing period disables the formation of a flat interface; (ii) a thermal bias caused a slightly tilted planar solidification front; and (iii) growth of the metastable pro-peritectic α-phase led to the formation of a supersaturated solid that solidified with an intriguing low growth rate.

A Three-Stage Solidification Model for Food Particles

A three-stage solidification model for food droplets has been implemented in a computational fluid dynamics code. It comprises of an initial cooling stage that is based on the principles of convective heat transfer. This is followed by the solidification period that is initiated once the droplet cools to a phase change temperature. Finally, when the droplet is completely solidified, the tempering phase begins where the droplet cools to the temperature of the ambient air. The model has been validated with respect to the experimental data for cocoa butter. Additional simulations were made in which the crystallization behavior of the cocoa butter droplets in relation to the droplet size, ambient air temperature and the relative drop-gas velocity was investigated. It was found that the crystallization time is exponentially related to the droplet size. Further, it increased with the ambient temperature, but decreased with the relative drop-gas velocity. Overall, the results suggest operating at the extreme values of the process parameters, requiring high amount of energy, to minimize the crystallization time. It was concluded that there is a need for optimizing the operating conditions of the powder production process to minimize the energy requirement of the system while maintaining a reasonable crystallization time.

Characteristic study of modified nano CuO powder-based paraffin composite and its experimental investigation of melting/solidification behavior for mobilized cold thermal storage systems

The low thermal conductivity of Phase Change Materials (PCM) reduces its performance and remains a challenging issue. In the present study, modified nano copper oxide powder (CuO) with various weight percentages is dispersed into paraffin wax to form Nano-PCM composites (NPCM). Transmission Electron Microscopy analysis showed the uniform dispersion of modified CuO and spherical in structure. Diffraction Scanning Calorimeter analysis (DSC) showed a trivial difference in the melting point of PCM and NPCM. The peak melting temperature of PCM was 18.56°C and for NPCM with 1% concentration was 17.14°C. The thermal conductivity of NPCM in solid and liquid states was high when compared to that of pure PCM. The thermal conductivity of NPCM with a 1% concentration is enhanced by 52% in a solid state and 20% in a liquid state. Solidification/Melting experiments conducted at different bath temperatures such as 15°C, 17°C, and 19°C for PCM and NPCM revealed that the solidification period and melting period reduced with an increase in concentrations of modified Nano CuO due to augmented heat transfer rates. The solidification time for NPCM with 1% concentration is reduced by 18.33% for discharging temperature 25°C, and melting time are reduced by 16.6% for charging temperature.

Solidification characteristics in a spherical capsule integrated with pin fins and rectangular fins - a comparative study

This study aims at investigating the solidification characteristics in a spherical capsule with pin fins and rectangular fins of same length and volume immersed in a constant temperature bath (-6°C, -9°C, -12°C). The fins are made of copper and are attached to the inner surface of the spherical capsule. The fin lengths correspond to the annulus fill volume margin of 75% taken on the inside wall of the spherical container. The findings showed that the overall solidification period of the capsules with rectangular fins was reduced. Also, the subcooling phenomena is completely eliminated at bath temperature of -6°C. Results also indicated that 50% PCM mass is reduced effectively with the provision of fins. Thus, with the employment of rectangular fins better potential energy savings can be attained when operated at partial charging mode at higher bath temperature.