Flow Mechanism for Stall Margin Improvement via Axial Slot Casing Treatment on a Transonic Axial Compressor

Axial slot CTs were designed and applied on Rotor 67 to understand the physical mechanisms responsible for the improvement of the stall margin. Unsteady Reynolds-averaged Navier-Stokes was applied in addition to steady Reynolds-averaged Navier-Stokes to simulate the flow field of the rotor. The results show that aerodynamic performance and the rotor stability were improved. Stall margin improvement (SMI) improved by 26.85% after the CT covering 50% of the axial tip chord was applied, whereas peak efficiency (PE) decreased the least. The main reason for the rotor stall in the solid casing is the blockage caused by tip leakage flow. After axial slot CTs were applied, the tip leakage flow in the front part of the chord was obviously reduced, and the majority of the blockages in the tip region were removed. The absolute value of the axial momentum before 45% axial chord in CT_50 was reduced by 50%, whereas the maximum tangential momentum value of CT_50 was decreased by 70% relative to the solid casing. CT_50 configuration was located across the shock wave; thus, it can fully utilize the pressure gradient to bleed and remove the blockage region, and the across flow is considerably depressed

A design database representation and evolution model

Bibliography: p. 160-17

Lead-free (Ba,Sr)TiO3 – BiFeO3 based multilayer ceramic capacitors with high energy density

High recoverable energy density (10 J cm−3) multilayers have been fabricated from lead-free 0.61BiFeO3-0.33(Ba0.8Sr0.2)TiO3-0.06La(Mg2/3Nb1/3)O3 ceramics. High breakdown strength > 730 kV cm-1 was achieved through the optimisation of multilayer processing to produce defect-free dielectric layers 7 μm thick. Excellent temperature, frequency, fatigue stability and fast charge-discharge speed were observed in the multilayer, critical for their potential use in power electronics

Electrochemical Cutting in Weak Aqueous Electrolytes: The Strategy for Efficient and Controllable Preparation of Graphene Quantum Dots

The controllable and efficient electrochemical preparation of highly crystalline graphene quantum dots (GQDs) in an aqueous system is still challenging. Here, we developed a weak electrolyte-based (typically an ammonia solution) electrochemical method to enhance the oxidation and cutting process and therefore achieve a high yield of GQDs. The yield of GQDs (3–8 nm) is 28%, approximately 28 times higher than the yield of GQDs prepared by other strong electrolytes. The whole preparation process can be accomplished within 2 h because of the effective free radical oxidation process and the suppressed intercalation-induced exfoliation in weakly ionized aqueous electrolytes. The GQDs also showed excellent crystallinity which is obviously better than the crystallinity of GQDs obtained via bottom-up approaches. Moreover, amino-functionalization of GQDs can be realized by manipulating the electrolyte concentration. We further demonstrate that the proposed method can also be expanded to other weak electrolytes (such as HF and H₂S) and different anode precursor materials (such as graphene/graphite papers, carbon fibers, and carbon nanotubes)

Green and Mild Oxidation: An Efficient Strategy toward Water-Dispersible Graphene

Scalable fabrication of water-dispersible graphene (W-Gr) is highly desirable yet technically challenging for most practical applications of graphene. Herein, a green and mild oxidation strategy to prepare bulk W-Gr (dispersion, slurry, and powder) with high yield was proposed by fully exploiting structure defects of thermally reduced graphene oxide (TRGO) and oxidizing radicals generated from hydrogen peroxide (H₂O₂). Owing to the increased carboxyl group from the mild oxidation process, the obtained W-Gr can be redispersed in low-boiling solvents with a reasonable concentration. Benefiting from the modified surface chemistry, macroscopic samples processed from the W-Gr show good hydrophilicity (water contact angle of 55.7°) and excellent biocompatibility, which is expected to be an alternative biomaterial for bone, vessel, and skin regeneration. In addition, the green and mild oxidation strategy is also proven to be effective for dispersing other carbon nanomaterials in a water system