Enhancement of Mixing Performance of Non-Newtonian Fluids using Curving and Grooving of Microchannels

In this study, a numerical investigation was performed on the mixing of non-Newtonian power-law fluids in curved micromixers with power-law indices between 0.49 and 1 and Reynolds numbers between 0.1-300. The properties of water and CMC solution were used for simulation of Newtonian and non-Newtonian fluid flows, respectively. The effects of grooves embedded on the bottom wall of micromixers and geometrical parameters such as depth and angle of grooves on mixing performance were examined. The mixing of non-Newtonian fluids using this kind of micromixers has not been studied before. Eventually, using of inclined grooves with 30° inclination angle was studied. Open source CFD code of OpenFOAM was utilized to simulate the mixing process. The results showed that the grooves caused chaotic advection and improved the mixing performance but had no significant effect on dimensionless pressure drop. Also, the grooves with 30◦ angle showed better mixing index for all values of power-law indices

Application of Electric Field to Developing Falling Films using Wire-Plate Electrode Configuration- An Experimental Study

Experimental investigation of Electrohydrodynamic developing falling film flow of transformer oil has been conducted within an inclined rectangular channel and hydrodynamic characteristics of the flow have been revealed. The electric field has been generated by five overhead thin wire electrodes connected to the positive high DC voltage on the air and the grounded plate electrodes which are placed upon the floor of the channel. It is the first time that the wavy behavior on a liquid falling film's interface has been created by this electrode configuration. A non-intrusive method has been used to measure the local flow structure by a high-speed camera, then statistical characteristics of the wavy falling film have been computed by image processing of the captured video frames. By applying 13-16 kV to the wire electrodes, the influence of EHD force on the wavy behavior of falling film has been conducted for Reynolds number 10-120 in the laminar-wavy regime at three different inclination angles 15◦, 30◦ and 45°. The vertical distance of the high-voltage wire electrodes to ground electrodes has been set to 14 mm. The liquid velocity, film thickness, and wave frequency have been measured for non-electrified and electrified falling film, and their results have been evaluated with other experimental studies and an acceptable agreement has been obtained. The results indicate that the proposed HV wire-grounded plate electrode configuration in this study does not disturb the original structure of the falling film and by intensifying the wavy behavior of laminar falling film can either suppress or enhance heat/mass transfer rate. The effects of the applied voltage on the frequency, velocity and film thickness of the falling liquid film have been also discussed in detail

Heat Transfer Enhancement in a Stagnant Dielectric Liquid by the Up and Down Motion of Conductive Particles Induced by Coulomb Forces

When charged particles are exposed to an electric field the well-known Coulomb force acts on them. In this investigation, this force is utilized to induce vertical motion of spherical steel particles submerged in a dielectric liquid. The interelectrode space of a two parallel electrode system is filled with the liquid and dispersed steel particles, which become charged after contact with the electrodes. Experiments were carried out to measure the effect of this particle motion on the heat transfer between an electrode surface and an adjacent stagnant dielectric liquid. In order to interpret the experimental data, the dynamics of particles was analytically studied for low particle volume concentrations. Experimental results demonstrate significant heat transfer enhancement on low viscosity dielectric liquids. A detailed discussion is presented on the possible mechanisms responsible for such an enhancement