Effect of flanged diffuser divergence angle on wind turbine: A numerical investigation.

Power augmentation in a small-scale horizontal axis wind turbine, with its rotor encased in a flanged diffuser is explored. The power output of the wind turbine varies with changes in the diffuser design and the resulting back pressure. Reduction in this back pressure also results in early flow separation at the diffuser surface, which hinders turbine performance. The main aim of this study is to numerically investigate the local configuration of the wind turbine location inside the diffuser by varying diffuser angles and wind speeds. Therefore, shroud and flange were modeled and analyzed using the computational fluid dynamic (CFD) analyses and experiments were performed at two wind speeds 6 m/s and 8 m/s with and without the diffuser for model validation. The divergence angle of 4° was found to have no flow separation, thus maximizing flow rate. The proposed design shows wind speed improvement of up to 1.68 times compared to the baseline configuration. The corresponding optimum flange height was found to be 250 mm. However, increasing the divergence angle had a similar output. The dimensionless location of wind turbine was found to be between 0.45 and 0.5 for 2° and 4° divergence angle respectively. Furthermore, the maximum augmentation location varies with wind speed and diffuser's divergence angle as described by dimensionless location of wind turbine, thus presenting a noteworthy contribution to the horizontal axis wind turbine area with the flanged diffuser.

Analysis of Particle Size and Concentration in Die Sinking Electric Discharge Machining.

Electric discharge machining with a powder mix dielectric is a promising technique to harden a work piece's surface using electricity with a high energy density. The quality of the electrical discharge-machined surface is related to its surface integrity in which the surface's roughness, residual stresses, micro hardness and surface micro cracks are some of the major factors. In this research, graphite powder was mixed in a dielectric with a particle size of 20 µm, 30 µm, and 40 µm, with the concentration of the graphite powder ranging from 2 g/L to 4 g/L. Moreover, the peak current and pulse time on were also coupled with an additive of graphite powder to investigate the effect on the surface quality, i.e., the recast layer thickness, micro hardness and crater depth as well as the material removal rate (MRR) and tool wear rate (TWR). A Box-Behnken design was employed to design the experiments and the experimental results revealed that the graphite powder size and concentration coupled with the electrical parameters (peak current and pulse time on) significantly influenced the recast layer thickness, micro hardness, crater size, MRR and TWR. The crater depth and micro hardness were maximized at a higher concentration and particle size, while the recast layer thickness was reduced with a higher gain size.

Numerical Analysis of a Liquid Nitrogen (LN2) Engine for Efficient Energy Conversion.

A liquid fuel that produces no toxic exhaust could help reduce pollution, potentially in urban areas. In this study, a simulation was conducted using the AVL Boost platform, on the use of liquid nitrogen (LN2) in a four-stroke engine. This study is focused on engine performance using directly introduced LN2 and the analysis of related aspects (inlet, outlet, and in-cylinder pressure, temperature, conditions for LN2 evaporation, etc.) that indicate the possible potential for the development of a zero-emission direct injection internal evaporation (DI-IE) LN2 engine. AVL Boost software was uniquely customized to accommodate the simulations, as modeling with LN2 was not available in the standard features. Simulation results, including indicated mean effective pressure (IMEP), effective torque, and power, were compared with similarly sized diesel and gasoline engines running at speeds of up to 1000 rpm. The LN2 injection mass was matched with air intake to evaluate the optimal combination. The simulation results showed that the enthalpy of the aspirated air was sufficient to evaporate and expand the injected amount of LN2 in each cycle, generating the in-cylinder pressure for the power stroke. The IMEP of the LN2 engine was similar to internal combustion engines, and its indicated efficiency was about four times higher (56-62%). The air separation process was 44% efficient in producing the required LN2, making the overall efficiency about 31%.