Numerical Study on the Thermal Field and Heat Transfer Characteristics of a Hexagonal-Close-Packed Pebble Bed

Fuel elements in a high-temperature gas-cooled reactor (HTGR) core may be stacked with a hexagonal close-packed (HCP) structure; therefore, analyzing the temperature distribution and heat transfer efficiency in the HCP pebble bed is of great significance to the design and safety of HTGR cores. In this study, the heat transfer characteristics of an HCP pebble bed are studied using CFD. The thermal fields and convective heat transfer coefficients under different coolant inlet velocities are obtained, and the velocity fields in the gap areas are also analyzed in different planes. It is found that the strongest heat transfer is shown near the right vertices of the top and bottom spheres, while the weakest heat transfer takes place in areas near the contact points where no fluid flows over; in addition, the correlation of the overall heat transfer coefficient with the Reynolds number is proposed as havg = 0.1545(k/L)Re0.8 (Pr = 0.712, 1.6 × 104 ≤ Re ≤ 4 × 104). It is also found that the heat transfer intensity of the HCP structure is weaker than that of the face-centered-cubic structure. These findings provide a reference for reactor designers and will contribute to the development of safer pebble-bed cores.

Numerical Investigation into Photovoltaic Performance of Organolead Trihalide Perovskite Quantum Dot Intermediate Band Solar Cell

In this work, an intermediate band solar cell (IBSC) model consisting of MAPbI3 quantum dots (QD) and MAPbCl3 barrier material is explored analytically with MATLAB. Titanium di-oxide (TiO2) is used as transport layer for electron and Spiro-OMeTAD (2,2',7,7'-tet-rakis (N,N'-di-p-methoxyphenylamine)–9,9' spirobifluorene) is used as transport layer for hole. Fluorine-doped tin oxide (FTO) and Silver (Ag) is used as top and bottom contact. The impact of QD size and dot spacing on the key parameters of MAPbI3 QD-IBSC is illustrated throughout this paper. In order to identify the number of IB in a single regime, Schrödinger equation is solved as a function of host energy gap using Kronig–Penney model. The detailed balance limit assumptions with unity fill factor are applied to extract highest efficiency from the system. For any case, face centered cubic (FCC) crystal structure is assumed. The (100) crystal orientation is considered as charge carriers from n–region to p–region transport in this orientation. Major performance indicators of the device such as photocurrent intensity Jsc, open circuit voltage Voc and power conversion efficiency η have been delineated. Highest efficiency of 63% is attained for dot size of 4 nm and dot spacing of 1.5 nm.

Formation and Anisotropic Mechanical Behavior of Stacking Fault Tetrahedron in Ni and CoCrFeNiMn High-Entropy Alloy

Stacking fault tetrahedron (SFT) is a kind of detrimental three-dimensional defect in conventional face-centered cubic (FCC) structural metals; however, its formation and anisotropic mechanical behavior in a CoCrFeNiMn high-entropy alloy (HEA) remain unclear. In this work, we first performed molecular dynamics simulations to verify the applicability of the Silcox-Hirsch mechanism in the CoCrFeNiMn HEA. The mechanical responses of the SFT to shear stress in different directions and that of the pure Ni counterpart were simulated, and the evolutions of the atomic structures of the SFTs during shear were analyzed in detail. Our results revealed that the evolution of the SFT has different patterns, including the annihilation of stacking faults, the formation and expansion of new stacking faults, and insignificant changes in stacking faults. It was found that the effects of SFT on the elastic properties of Ni and HEA are negligible. However, the introduction of SFT would reduce the critical stress, while the critical stress of the CoCrFeNiMn HEA is much less sensitive to SFT than that of Ni.

Self-Assembled Corn-Husk-Shaped Fullerene Crystals as Excellent Acid Vapor Sensors

Low-molecular-weight acid vapors cause aging and destruction in material processing. In this paper, facile fabrication of novel corn-husk-shaped fullerene C60 crystals (CHFCs) through the dynamic liquid–liquid interfacial precipitation method is reported. The CHFCs were grown at the liquid–liquid interface between isopropyl alcohol (IPA) and a saturated solution of C60 in mesitylene under ambient temperature and pressure conditions. The average length, outer diameter, and inner diameter of CHFCs were ca. 2.88 μm, 672 nm, and 473 nm, respectively. X-ray diffraction (XRD) analysis showed the CHFCs exhibit a mixed face-centered cubic (fcc) and hexagonal-close pack (hcp) crystal phases with lattice parameters a = 1.425 nm, V = 2.899 nm3 for fcc phase and a = 2.182 nm, c = 0.936 nm, a/c ratio = 2.33, and V = 3.859 nm3 for hcp phase. The CHFCs possess mesoporous structure as confirmed by transmission electron microscopy (TEM) and nitrogen sorption analysis. The specific surface area and the pore volume were ca. 57.3 m2 g−1 and 0.149 cm3 g−1, respectively, are higher than the nonporous pristine fullerene C60. Quartz crystal microbalance (QCM) sensing results show the excellent sensing performance CHFCs sensitive to acetic acid vapors due to the enhanced diffusion via mesoporous architecture and hollow structure of the CHFCs, demonstrating the potential of the material for the development of a new sensor system for aliphatic acid vapors sensing.

GC/MS Analysis and Phyto-synthesis of Silver Nanoparticles Using Amygdalus spinosissima Extract: Antibacterial, Antioxidant Effects, Anticancer and Apoptotic Effects

Background: The present study was aimed at phyto-synthesized silver nanoparticles (AgNPs) using Amygdalus spinosissima (A. spinosissima) extract and to investigate the antibacterial, antioxidant effects, anticancer and apoptotic effects of phyto-synthe-sized AgNPs. Methods: The bio-fabricated AgNPs were characterized using UV-visible spectroscopy (UV-visible), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy Disper-sive X-ray (EDX). Results: The phyto-synthesized AgNPs showed maximum absorption in 438 nm, in the UV-visible spectrum. XRD peaks were observed at 2θ values in 38.20°, 44.40°, 64.60°, and 77.50° which are indexed as (111), (200), (220), and (311) bands of Face-Centered Cubic (FCC) structures of silver. FTIR analysis indicated that the AgNPs were capped with A. spinosissima extract. SEM and TEM micrographs revealed that the fabricated AgNPs were spherical and the average size range was 17.89 nm. Also, the EDX results show that the content of Ag was 90%. Conclusion: The phyto-synthesized AgNPs had significant antibacterial activity against Gram-negative bacteria, as well as, the AgNPs exhibited great inhibitory effects on DPPH radicals and their antioxidant properties were favorably comparable to the antioxidant outcomes of ascorbic acid. Moreover, the AgNPs showed anti-cancer activity against the MCF-7 cell line with the IC50=6.1 µg/ml. Moreover, the phyto-synthesized AgNPs could induce apoptosis in the MCF-7 cell line significantly. The GC-MS analysis of the A. spinosissima extract showed that 102 bioactive phyto-chemical compounds, which be of use to the synthesis of AgNPs.

Localization of Plastic Deformation in the Copper and Stainless Steels Samples, Irradiated with Neutrons

The reduction of ductility of austenitic stainless steels as a result of long-term operation in the nuclear reactor core is an important problem of modern radiation materials science. Understanding the mechanisms of the effect of neutron irradiation on the mechanical properties of austenitic steels is impossible without research of localization processes occurring during the deformation. In this paper, it was found that the value of the true local deformation corresponding to the onset of neck formation in face-centered cubic structured metals decreases with an increase in the radiation dose, while the true stress remains almost constant. Additional hardening of AISI 304 steel due to the intensive formation of the martensitic α’-phase increases not only the stress at which a neck is formed in this alloy, but also the true local deformation. As a result, the uniform elongation increases and remains high after neutron irradiation to 0.05 dpa. The forehanded formation of the martensitic α’-phase in sufficient quantity before the necking onset can be considered as an additional deformation mechanism that will increase the ability of the material to deform uniformly.