The objective of this paper is to analyze the effect of hydraulic diameter and channel shape on the thermal and hydrodynamic characteristics of a microchannel cooled by Graphene-Platinum/water hybrid nanofluid for electronic cooling applications. The study was performed numerically using mathematical software called Maple 19.0. Microchannels having square and rectangular cross-sections, and hydraulic diameters ranging from 200 µm to 1000 µm were taken into consideration. Thermal resistance, heat transfer coefficient, pressure drop and friction factor were evaluated for different conditions and their corresponding graphs are presented and discussed. It was evident from the results that low thermal resistance and high heat transfer coefficient was achieved upon decreasing the hydraulic diameter, which is favorable for the cooling of electronic chips and devices. Based on the Reynolds number, the heat transfer coefficient increased by 2 to 4 times for both rectangular and square microchannels, on decreasing the hydraulic diameter from highest value (1000 µm) to lowest value (200 µm). However, friction factor and pressure drop increased for channels with lower hydraulic diameters. In addition, rectangular microchannels exhibited better heat transfer performance, while square microchannels had lower friction factor and pressure drop. Rectangular microchannels presented a maximum enhancement of 30% in heat transfer coefficient and a reduction of 18% in thermal resistance, when compared to square microchannels. The results also suggested that the performance of microchannels with 500 µm hydraulic diameter is balanced, considering both heat transfer performance and pressure drop constraints.

The performance of the compressor blade is considerably influenced by secondary flow effects, like the cross flow on the end wall as well as corner flow separation between the wall and the blade. Computational Fluid Dynamics (CFD) has been extensively used to analyze the flow through rotating machineries, in general and through axial compressors, in particular. The present work is focused on the studying the effects of Vortex Generator (VG) on test compressor at CSIR National Aerospace Laboratories, Bangalore, India using CFD. The compressor consists of NACA transonic rotor with 21 blades and subsonic stator with 18 vanes. The design pressure ratio is 1.35 at 12930 RPM with a mass flow rate of 22 kg/s. Three configurations of counter rotating VGs were selected for the analysis with 0.25δ, 0.5δ and δ height, where δ was equal to the physical thickness of boundary layer (8mm) at inlet to the compressor rotor [11]. The vortex generators were placed inside the casing at 18 percent of the chord ahead to the leading edge of the rotor. A total of 63 pairs of VGs were incorporated, with three pairs in one blade passage. Among the three configurations, the first configuration has greater impact on the end wall cross flow and flow deflection which resulted in enhanced numerical stall margin of 3.5% from baseline at design speed. The reasons for this numerical stall margin improvement are discussed in detail.

Micro parts have become inevitable nowadays for a large number of applications in the areas such as space technology, medical science, nano technology, and electronics. This creates a significant need to develop new techniques, and machine tools for micro manufacturing. In the micromanufacturing process, the interfacial friction between the forming tool and the workpiece is uncertain. It has a significant impact on process workability, which is a key factor in material formability. In the current work microtribological behavior of hexagonal 2D-SnS2 nanosheets as lubricating additives is investigated. Upon the usage of nanoadditive lubricant in the extrusion of micro stepped pin, the extrusion force reduced significantly. Due to the presence of nanoadditives an increased surface quality in the extrudates was observed and it was further justified in the surface roughness results. The raise in temperature leads to more uniform hardness, with a significant reduction of coefficient of variation along with improved material formability. This research work provides a deeper understanding of the characteristics of nanoadditive lubricant and its tribological behavior in the microextrusion process.