Dewan Hasan Ahmed

Numerical Study for the Effect of Inlet Humidity Condition at PEMFC Channel

PEMFC(Proton Exchange Membrane Fuel Cell) is a low temperature fuel cell and has many probabilities of commercial use. However, water management is one of the serious technical problems for commercialization. It is necessary to understand the relationship between operation conditions and water behavior in PEMFC channel because it affects fuel cell performance. In this paper, the distribution of current density according to inlet humidity condition is mainly observed and discussed. If the anode inlet is well humidified, electro-osmotic drag is very active. For this reason, current density is very high at inlet side and the distribution is non-uniform.

Optical Trapping Forces on Non-Spherical Particles in Fluid Flows

The optical stability of particles above a waveguide surface depends on the forces induced by fluid drag and the electromagnetic field. The optical trapping forces on non-spherical particles were examined for various flow conditions. A three-dimensional finite element method was employed to calculate the electromagnetic field and the fluid flow. It was found that the stability of non-spherical particles is significantly affected by the fluid velocity and the orientation of the particles. The downward trapping force meant that non-spherical particles are more stable at higher Reynolds numbers. The length of the particle in the transverse direction also had a significant impact on particle stability. The present model was tested against previously reported results.

Optical Forces on Non-Spherical Nanoparticles Trapped by Optical Waveguides

Numerical simulations of a solid-core polymer waveguide structure were performed to calculate the trapping efficiencies of particles with nanoscale dimensions smaller than the wavelength of the trapping beam. A three-dimensional (3-D) finite element method was employed to calculate the electromagnetic field. The inlet and outlet boundary conditions were obtained using an eigenvalue solver to determine the guided and evanescent mode profiles. The Maxwell stress tensor was considered for the calculation of the transverse and downward trapping efficiencies. A particle at the center of the waveguide showed minimal transverse trapping efficiency and maximal downward trapping efficiency. This trend gradually reversed as the particle moved away from the center of the waveguide. Particles with larger surface areas exhibited higher trapping efficiencies and tended to be trapped near the waveguide. Particles displaced from the wave input tended to be trapped at the waveguide surface. Simulation of an ellipsoidal particle showed that the orientation of the major axis along the waveguides lateral z-coordinate significantly influenced the trapping efficiency. The particle dimensions along the z-coordinate were more critical than the gap distance (vertical displacement from the floor of the waveguide) between the ellipsoid particle and the waveguide. The present model was validated using the available results reported in the literature for different trapping efficiencies.

Non-Newtonian effect on ink transfer for gravureoffset printing

A computational simulation is carried out with the Carreau model to explore the non-Newtonian behavior of ink for gravure-offset printing. The volume of fluid (VOF) model is adopted to demonstrate the stretching and breakup behaviors of ink. The results indicate that the ink transfer ratio is much influenced by contact angle especially by the contact angle of upper plate (α). The ink transfer of non-Newtonian fluid shows a quite different trend from that of Newtonian fluid. An oscillation or unstable behavior of the position of the minimum thickness of ink between two parallel plates during the stretching period of ink is observed for lower values of α. This oscillation gradually diminishes for higher contact angles at the upper plate. Moreover, the velocity of the upper plate has negative impact on the ink transfer ratio. The results are validated with available data from literature.