Sample mixing is difficult in microfluidic devices because of laminar flow. Micromixers are designed to ensure the optimal use of miniaturized devices. The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency. A serpentine-shaped microchannel with sinusoidal side walls was designed, and three cases, with amplitude to wavelength (A/λ) ratios of 0.1, 0.15, and 0.2 were investigated. Numerical simulations were conducted using the Navier–Stokes equations, to determine the flow field. The flow was then coupled with the convection–diffusion equation to obtain the species concentration distribution. The mixing performance of sinusoidal walled channels was compared with that of a simple serpentine channel for Reynolds numbers ranging from 0.1 to 50. Secondary flows were observed at high Reynolds numbers that mixed the fluid streams. These flows were dominant in the proposed sinusoidal walled channels, thereby showing better mixing performance than the simple serpentine channel at similar or less mixing cost. Higher mixing efficiency was obtained by increasing the A/λ ratio.

The spray characteristics play a crucial role in determining the performance and emissions of compression ignition (CI) engines at the pre-combustion stage. With the advent of many types of alternative fuels and their blends with diesel, it is necessary to investigate the effect of fuel properties and various injection conditions to determine the penetration length, spray cone angle and spray area for a viable fuel with similar or better dispersion characteristics to diesel. Hence, this study reviews and summarizes the spray visualization techniques, along with in depth analysis of macroscopic spray properties of various fuel blends with diesel. It was found that higher injection pressures typically led to higher penetration lengths, better atomization with reduced Sauter mean diameter. Liquid properties such as viscosity, surface tension, and evaporation as well as structural properties play a crucial role in spray formation in fuel blends with various types of alcohols, ethers, biodiesel, aliphatic, aromatic, as well as nanoparticle additives. This review compares these fuel additives and their types to present a comparative study with diesel to determine the ideal conditions with minimal changes to the engine for replacing diesel with a sustainable fuel consisting of better combustion efficiency due to its enhanced spray characteristics.

Heat transfer enhancement using the passive method of surface enhancers in microchannel heat sinks (MCHS) is always accompanied by increase in pressure drop and pumping power requirement. To reduce the pressure drop, a novel method of surface refinement is being proposed by transforming the ribs like surface enhancers to streamlined structures of the same cross-section. The performance of MCHS with and without surface refinement has been compared by evaluating pressure drop, Nusselt number and thermal enhancement factor for Reynolds number in the range of 100–1,000. The coning action of ribs results in a tremendous reduction in pressure drop with a negligible reduction in heat transfer thus, leading to a higher thermal enhancement factor for cones than ribs. Moreover, the performance improvement of various refined surfaces has been evaluated by computing percentage changes in pressure drop, Nusselt number, and thermal enhancement factor. Among all the cases, the surface refinement of the ribs has resulted in a maximum pressure drop reduction of 85% whereas the maximum reduction in Nusselt number is 25%; thereby achieving a thermal enhancement factor of 80%. The proposed surface refinement is expected to enhance the thermo-hydraulic characteristics as well as the energy consumptions of future generations of microelectronics.