Search Results (12)

Sanicro 25 (X7NiCrWCuCoNb25-23-3-3-2) steel is specifically designed for use in superheater components within the latest generation of conventional power plants. These power plants operate under conditions often referred to as super-ultra-supercritical, with steam parameters that can reach up to 30 MPa and temperatures of 653 °C for fresh steam and 672 °C for reheated steam. While last-generation supercritical power plants still rely on fossil fuels, they represent a significant step forward in more sustainable energy production. The most sophisticated facilities of this kind can achieve thermodynamic efficiencies exceeding 47%. This study aimed to conduct a detailed analysis of the initial precipitation processes occurring in Sanicro 25 steel within the temperature range of 700–900 °C. The temperature of 700 °C corresponds to the operational conditions of this material, particularly in secondary steam superheaters in thermal power plants that operate under ultra-supercritical parameters. Understanding precipitation processes is crucial for optimizing mechanical performance, particularly in terms of long-term strength and creep resistance. To accurately assess the microstructural changes that occur during the early stages of service, a digital twin approach was employed, which included CALPHAD simulations and experimental heat treatments. Experimental annealing tests were conducted in air within the temperature range of 700–900 °C. Precipitation behavior was simulated using the Thermo-Calc 2025a with Dictra software package. The results from Prisma simulations correlated well with the experimental data related to the kinetics of phase transformations; however, it was noted that the predicted sizes of the precipitates were generally smaller than those observed in experiments. Additionally, computational limitations were encountered during some simulations due to the complexity arising from the numerous alloying elements present in Sanicro 25 steel. The microstructural evolution was investigated using various methods, including light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Full article

The escalating heat flux densities in high-performance electronics necessitate superior thermal management. This study enhanced pool-boiling heat transfer, a method offering high heat removal capacity, by leveraging Binder Jetting 3D Printing (BJ3DP) to create complex porous copper structures without the need for chemical treatments. This approach enables a reliable utilization of phenomena like capillarity for improved performance. Three types of porous copper structures, namely Large Lattice, Small Lattice, and Staggered, were fabricated on pure copper substrates and tested via pool boiling of de-ionized and de-gassed water at atmospheric pressure. Compared to a plain polished copper surface, which exhibited a critical heat flux (CHF) of 782 kW/m² at a wall superheat of 18 K, the 3D-printed porous copper surfaces showed significantly improved heat transfer performance. The Staggered surface achieved a conventional CHF of 2342.4 kW/m² (a 199.7% enhancement) at a wall superheat of 24.6 K. Notably, the Large Lattice and Small Lattice structures demonstrated exceptionally stable boiling without reaching the typical catastrophic CHF within the experimental parameters. These geometries continued to increase in heat flux, reaching maximums of 2397.7 kW/m² (206.8% higher at a wall superheat of 55.6 K) and 2577.2 kW/m² (229.7% higher at a wall superheat of 39.5 K), respectively. Subsequently, a gradual decline in heat flux was observed with an increasing wall superheat, demonstrating an outstanding resistance to the boiling crisis. These improvements are attributed to the formation of distinct vapor–liquid pathways within the porous structures, which promotes the efficient rewetting of the heated surface through capillary action. This mechanism supports a highly efficient, self-sustaining boiling configuration, emphasizing the superior rewetting and vapor management capabilities of these 3D-printed porous structures, which extend the boundaries of sustained high heat flux performance. The porous surfaces also demonstrated a higher heat transfer coefficient (HTC), particularly at lower heat fluxes (≤750 kW/m²). High-speed digital camera visualization provided further insight into the boiling phenomenon. Overall, the findings demonstrate that these BJ3DP structured surfaces produce optimized vapor–liquid pathways and capillary-enhanced rewetting, offering significantly superior heat transfer performance compared to smooth surfaces and highlighting their potential for advanced thermal management. Full article

The present work was undertaken to explore the multiple alloys and process steps that have been suggested to mitigate the harmful effects of high iron content in cast Al-Si alloys. The base alloy used was ommercial 413.0 alloy containing 0.35%Mg. Iron was added at three Fe levels up to 1.8%. The addition of Sr, 1.0%Zn, 0.2%Ti were made to the alloys so prepared, which were melted and maintained at a superheat of 750 °C or 950 °C. The melts were poured in different molds that produced three solidification rates. In total, 40 castings were prepared: half of the castings were used for metallographic examinations in the as-cast condition, while the other half were set aside for tensile testing following T6 treatment. The results show that at a solidification rate of 50 °C/s, 1.8%Fe could be dissolved in the aluminum matrix regardless of other melt treatments. With regard to the other solidification rates, superheating at 950 °C, coupled with Sr addition or Sr + Be, reduces the average β-platelets length by 80% (0.8 °C/s) or 95% (8 °C/s). The addition of P causes a marked drop in the alloy tensile strength due to the precipitation of primary Si, Al₂Si₂Sr, and β-AlFeSi hard-phase particles. Therefore, reducing the iron content in the castings may be considered a major objective to be recommended for developing alloys with higher strength and optimum quality values. More than 1000 tensile bars were tested in this study. Full article

Radiotherapy treatment plans have become highly conformal, posing additional constraints on the accuracy of treatment delivery. Here, we explore the use of radiation-sensitive ultrasound contrast agents (superheated phase-change nanodroplets) as dosimetric radiation sensors. In a series of experiments, we irradiated perfluorobutane nanodroplets dispersed in gel phantoms at various temperatures and assessed the radiation-induced nanodroplet vaporization events using offline or online ultrasound imaging. At 25 °C and 37 °C, the nanodroplet response was only present at higher photon energies (≥10 MV) and limited to <2 vaporization events per cm² per Gy. A strong response (~2000 vaporizations per cm² per Gy) was observed at 65 °C, suggesting radiation-induced nucleation of the droplet core at a sufficiently high degree of superheat. These results emphasize the need for alternative nanodroplet formulations, with a more volatile perfluorocarbon core, to enable in vivo photon dosimetry. The current nanodroplet formulation carries potential as an innovative gel dosimeter if an appropriate gel matrix can be found to ensure reproducibility. Eventually, the proposed technology might unlock unprecedented temporal and spatial resolution in image-based dosimetry, thanks to the combination of high-frame-rate ultrasound imaging and the detection of individual vaporization events, thereby addressing some of the burning challenges of new radiotherapy innovations. Full article

The laser treatment of surfaces enables the alteration of their morphology and makes them suitable for various applications. This paper discusses the use of a laser beam to develop surface features that enhance pool boiling heat transfer. Two types of structures (in the ‘macro’ and ‘micro’ scale) were created on the samples: microfins (grooves) and surface roughness. The impact of the pulse duration and scanning velocity on the height of the microfins and surface roughness at the bottom of the grooves was analyzed with a high precision optical profilometer and microscope. The results indicated that the highest microfins and surface roughness were obtained with a pulse duration of 250 ns and scanning velocity of 200 mm/s. In addition, the influence of the ‘macro’ and ‘micro’ scale modifications on the boiling heat transfer of distilled water and ethyl alcohol was studied on horizontal samples heated with an electric heater. The largest enhancement was obtained for the highest microfins and roughest surfaces, especially at small superheats. Heat flux dissipated from the samples containing microfins of 0.4 mm height was, maximally, over three times (for water) and two times (for ethanol) higher than for the samples with smaller microfins (0.2 mm high). Thus, a modification of a selected model of boiling heat transfer was developed so that it would be applicable to laser-processed surfaces. The correlation proved to be quite successful, with almost all experimental data falling within the ±100% agreement bands. Full article

This work focuses on the occurrence and composition of flammable pyrolysis gases which can be expected from stimulation of heavy oil with superheat steam. These gases can have commodity value or be used to fire a conventional boiler to generate steam vapor for superheater feed. Seven oil samples taken from different US locations were tested via thermogravimetric analysis (TGA) with off-gas analysis of light hydrocarbons via mass spectrometry (MS). The samples were heated up to 500 °C at 5 °C/min in a gas flow of moist carbon dioxide and held at 500 °C until no further mass loss was noted. Then, carbonaceous residue was exposed to air at 500 °C to determine enthalpy of combustion by differential scanning calorimetry (DSC). To demonstrate that pyrolysis was indeed occurring and not simple de-volatilization, a high-molecular-weight reagent-grade organic molecule, lactose, was first demonstrated to produce components of interest. After treatment under moist CO₂ at 500 °C, all samples were found to lose around 90% of mass, and the follow-up combustion process with air further reduced the residual mass to between 2% and 12%, which is presumed to be mineral matter and char. The light hydrocarbons methane, ethane, and propane, as well as hydrogen, were detected through MS during pyrolysis of each oil sample. Heavier hydrocarbons were not monitored but are assumed to have evolved, especially during periods where additional mass loss was occurring in the isothermal process, with minimal light hydrocarbon evolution. These results correspond to a possible concept of subsequent in situ combustion drive with or without heat scavenging following high-temperature pyrolysis from in situ superheat steam injection. Full article

Pulsed Magneto-Oscillation (PMO) is a newly developed and effective homogenization technique, and has been successfully applied in rectangular continuous casting, but its processing parameters and effective stability in round billet continuous casting have not been investigated. In this paper, the effects of PMO on the solidification structure and the macrosegregation of Φ 178 mm continuous casting round billets for low carbon alloy steel were studied by industrial experiments. The results show that PMO can stably increase the equiaxed grain area, and reduce the macrosegregation of billets. Moreover, it has strong adaptability to steel grade and continuous casting process parameters. Compared with the billets without PMO treatment, for 93.8% of billets (15 billets) solidified with PMO, the equiaxed grain area ratio increased by an average of 5.8%, while for 87.5% of billets (14 billets), the carbon segregation index range decreased by an average of 0.06, though different steel grades, superheat and casting speed were used in the experiment. It is believed that convection caused by Lorentz force can accelerate the heat dissipation of steel liquid, and reduce the temperature of a liquid at the solidification front, while the magnetic oscillation effect is conducive to dendrite fragmentation. Both effects lead to refinement of the solidification structure and reduction of macrosegregation. Full article

Grain refinement of magnesium (Mg) alloys has been a major research topic over the past decades as one of the effective approaches to increase their strength and ductility simultaneously. In this study, a brief review of the grain refinement of aluminum-bearing Mg alloys is included to provide an in-depth understanding of the detailed mechanisms of grain refinement of Mg alloys. Additionally, the effect of melt superheating on the grain refining of Mg–Al-based alloys has been investigated. It was confirmed that melt superheating caused a significant grain refining effect in the commercial purity (CP) of AZ91 alloy (0.25% Mn). Undercooling of 1.3 °C was observed before superheating and was noticeably reduced after the superheating process. A vacuum filtering experiment was conducted, which involves filtering the melts using fine metal porous filters to separate the particles in the melts. It was observed that a large amount of Al₈Mn₅ particles were generated in the commercial purity AZ91 alloy by the superheating process. However, because of the poor crystallographic matching between Al₈Mn₅ and Mg, Al₈Mn₅ was not considered the nucleation site for Mg grains. A master alloy containing ε-AlMn particles, which are in good crystallographic matching with Mg, was added, and it was found that the grain size of the commercial-grade AZ91 alloy was reduced. Therefore, it is suggested that Al₈Mn₅ particles, existing as a solid phase in the molten metal of the commercial AZ91 alloy could be transformed into ε-AlMn particles by the superheating process, and these particles can be effective nucleation sites for Mg grains. The transformation of Al₈Mn₅ into ε-AlMn is considered the main mechanism of grain refinement of the commercial purity of AZ91 alloy by superheating. Notably, the effect of grain refinement by superheating was not observed in the high-purity (HP) AZ91 alloy (0.006% Mn) because Al–Mn particles were likely not formed due to a very small quantity of manganese. Full article

This paper describes the influence of technological treatments (i.e., bending or welding) on the structural stability of SUPER304H austenitic steel used in reheaters and superheaters in fossil fuel power plants. Although the worldwide trend is transitioning to green power sources, the lifetime of existing power plants has to be prolonged until the transition is complete. Experimental material was tested in as-received state (straight tubes), bends, and homogeneous weld joints. Part of the specimens was solution-annealed after the technological operation. Afterwards, all the samples were thermally aged in furnace (650, 675 and 700 °C) for 7560–20,000 h. For comparison, bent specimens were placed at experimental sites on an operating powerplant for 10,000+ h. The long-term aging causes the formation of Cr-based carbides on the grain boundaries along with the Fe-Cr sigma phase. Combination of elevated temperature and residual stress accelerates formation of the sigma phase. This can be prevented by solution-annealing after bending. Mechanical properties were evaluated by Vickers hardness and tensile tests. The microstructure was observed using light optical microscopy (LOM) and scanning electron microscopy (SEM) with the energy-dispersive X-ray detector (EDXS). Electron backscatter diffraction (EBSD) and X-ray powder diffraction (XRPD) were used to characterize the brittle phases. Full article

Cooling in liquid nitrogen is a typical service condition of high-temperature superconducting wire, and the variation of boiling stages on the wire protective layers such as the brass layers could be crucial for the quench behavior of superconducting devices. In this study, the influence of brass surface morphology (parameters of surface roughness and fractal dimension) on the Leidenfrost effect (including the wall superheat at critical heat flux and the wall superheat at Leidenfrost point, which are respectively characterized by the temperatures of $\Delta T_{\mathrm{CHF}}$ and $\Delta T_{\mathrm{LP}}$) was studied. The surfaces of brass samples were polished by sandpaper to obtain different morphologies, which were characterized by using white light interferometer images, and the boiling curves were recorded and analyzed by Matlab with lumped parameter method. The experimental results demonstrated that the surface morphology of brass samples could influence the $\Delta T_{\mathrm{LP}}$ significantly, but had no clear relationship with the $\Delta T_{\mathrm{CHF}}$. Moreover, the multi-scaled analysis was carried out to explore the influencing mechanism of surface microstructure, the relationship between $\Delta T_{\mathrm{LP}}$ and scale was more clear when the scale was small, and the fractal dimension was calculated and discussed together with surface roughness. The findings of this study could be instructive for surface treatment of superconducting wires to suppress quench propagation. Full article

The paper discusses the complex effect of melt overheating with subsequent fast cooling down to the pouring temperature on the crystallization process, microstructure and mechanical properties of Al-Mg-Si aluminum alloy. The results obtained facilitated the establishment of rational modes of melt overheating, leading to a significant change in the dispersion and morphology of structural components. In particular, with an increase in the melt overheating temperature to 900 °C with holding and subsequent rapid cooling to the casting temperature, a decrease in the average size of dendritic cells of the aluminum solid solution from 39 μm to 13 μm was observed. We also noticed the refinement of eutectic inclusions of the Mg₂Si phase with compact morphology. An increased level of mechanical properties was noted; the maximum values of tensile strength and elongation reached 228 MPa and 5.24%, respectively, which exceeded the initial values by 22.5% and 52.3%, correspondingly. The microhardness of the aluminum solid solution sequentially increased from 38.21 to 56.5 HV with an increase in the temperature during melt overheating. According to the EDS linear scanning, an increase in the superheat temperature of the melt is accompanied by an increase in the degree of saturation of the solid solution with magnesium. Full article

The aluminum content in oriented silicon steel obviously influences its magnetic properties. In the current work, the movement and melting process of added aluminum particles during Ruhrstahl-Heraeus (RH) treatment were simulated using a mathematical approach, considering the effect of the multiphase fluid flow on the evolution of aluminum particles and the dissolved aluminum distribution. The current model was validated by the [Al] content in the molten steel measured by an industry experiment. Most of the added aluminum particles were melted within 5 s after they connected with the molten steel under the superheat of 28 K. The statistics of the melting time and trajectory length showed a normal distribution. Furthermore, both the melting time and the trajectory length of aluminum particles decreased as the superheat increased. Since the maximum mixing time may go up when the superheat is excessive, the suggested superheat should range from 20 K to 30 K during the RH refining process. Besides, an appropriate sampling position with a short mixing time was proposed. Full article