Influence of tilt angle and the number of guide vane blades towards the Savonius rotor performance

Additional guide vane (GV) to the Savonius rotor is used to overcome the low rotor efficiency. This study is experimentally carried out to know the influence of guide vane in improving two blades Savonius rotor performance. There were four designs of guide vane which are 4, 5, 6 blades and installed at different tilt angles, which were 0°, 20°, 40°, and 60°. The experiment was done under wind speed of 5.9 m/s, 7.0 m/s, 8.1 m/s, 9.3 m/s and 10.4 m/s. The results show that the 6 blades of GV at a 60° tilt angle attained the best Cp, which was 0.0279 at the tip speed ratio of 0.53. The Cp increased up to 40% with six blades of GV. Wind direction identified significantly affected the rotor performance. The rotor performed best on the wind direction of 0° attained Cp of 0.079, but when the wind direction was modified on 30°, the rotor with 6 GV attained Cp of 0.0153 did not perform better than without GV that produced Cp of 0.0166. The guide vanes improve the Savonius rotor performance compared to the rotor without a guide vane. However, the wind direction also needs to be considered no less important factor affecting the Savonius rotor performance

Effect of Boron Addition on the Precipitation Behavior of S31254

To reduce the precipitation of σ phases and to improve the hot workability of S31254 steels, boron has been added into the composition of S31254 to a concentration of 40 ppm. The precipitation behavior was investigated before and after the addition of boron in different S31254 alloys during the compression deformation, and the nose temperature at 950 °C and the phase dissolution temperature at 1074 °C were selected as the measurement temperature. The result showed that more σ phases were precipitated at the grain boundary of S31254 alloys, compared to the boron-added alloy. Meanwhile, the addition of 40 ppm boron into the alloys has obviously prevented the σ phases from the austenitic matrix, and it takes longer time for the precipitation of σ phase at 950 °C. The specific influence factors of boron on the precipitation of σ phases were also further discussed

Graphene/Cu composites: Electronic and mechanical properties by first-principles calculation

Graphene characterized with ultrahigh intrinsic strength and excellent electronic properties is an ideal material to reinforce metals without despairing their thermal and electrical properties. Here, the electronic and mechanical properties of graphene intercalated copper (graphene/Cu) composites are investigated using density functional theory calculations. Graphene/Cu systems present an excellent electrical conductivity and increasing Debye temperature from 335 K for pure Cu to over 535 K in regardless of stacking models. In addition to greatly enhanced Young's modulus (149%), shear modulus (156%) and bulk modulus (108%) compared to copper, the ultimate strength of graphene/Cu composites are enhanced by 174% and 162%, in x and y directions, respectively. The strengthening and toughening effects of graphene in the composites is originated from strain strengthening and load transfer, which is consistent with the experimental results. Based on this calculation, the strengthening mechanism can be understood, which explains many experimental observations and also provides us a guide to improve graphene/metal composites quality