This study developed a one-dimensional model for a bipolar membrane unit used in desalination stacks with the finite– element method (FEM) based Comsol Multiphysics software. The numerical model took into account the stationary transport of K+, Cl-, H+ and OH- ions inside a desalination channel unit using Nernst – Planck – Poisson equations and the Onsager theory of the Second Wien Effect for water dissociation under externally applied electrical fields. Electrochemical behaviour for the unit cell model was validated through the experimental current-voltage curve of a bipolar membrane, as it was reported in the literature. Influence of the anion–exchange layer (AEL) and cation–exchange layer (CEL) thickness variation and fixed charge concentration ratio in CEL/AEL regions upon specific desalination performance parameters, like co–ion leakage current, water dissociation turn-on voltage and water dissociation resistance were investigated here. Evolution of K+, Cl-, H+ and OH- ion concentration through specific compartments on the unit cell (electrolyte, AEL, CEL) at different potential drops across the membrane helped to understand the contribution of specific ionic fluxes at the total current through the system.
In this paper it was developed a Finite Element Method (FEM) model for the simulation of interfacial failure between two plies of an AS4/PEEK composite sample using Cohesive Zone Model (CZM), under the frame work of Comsol Multiphysics software. Mixed Mode Bending (MMB) method was considered here for the numerical implementation of progressive delamination propagating in composite specimens with pre-existing cracks. Volumetric strain and von Mises stress at the maximum load before fracture have been evaluated at here different ratios between mode II strain energy rate and total strain energy rate GII/GT = 20%, 50% and 80%.
A rectangular radial microchannel model having the same geometric dimensions as one type of microchannel placed on a PC-controlled centrifugal Disk: length ℓ = 2.1 cm, height h = 65 μm and width Δy = 320 μm was considered here from an experimental work reported in literature. Fluid flow transport through this standard channel was numerically developed with the Finite Element Method (FEM) based Comsol Multiphysics software, simulation performed at rotating speeds ω between 25 and 300 rad/s. Other three rotating microchannel models with different aspect ratios AR have been simulated after by increasing the channel height from 65μm to 160 μm, 200 μm and 240 μm and by maintaining the same width of 320 μm. From the simulations of standard experimental type channel resulted that even at 300 rad/s, transverse Coriolis force was only close to half of centrifugal force, no secondary flow being induced in this case and a diffusion-based mixing is developed for this particular channel geometry. The radially rotating channel model was validated after comparing the FEM results with results from other two commercial finite volume codes (CFX and Fluent) reported in a numerical research study of a microchannel with ℓ = 10 mm and Δy = h = 200 μm.
An important part of microfluidic device technology is based on passive (static) micromixers, with a structure of microchannels organized in special configurations, in order to produce an efficient mixing of different types of solutions. In this study it was developed numerically using the Finite Element Method (FEM) based Comsol Multiphysics software a special type of Split and Recombine (SAR) micromixer model with two mixing units, based on a Grey topology. Three types of glycerol - water solutions have been considered for the performance investigation of this SAR mixing model. Degrees of mixing δm of 0.74 and 0.73 were computed for the water based solutions having 10% wt. glycerol and 20% wt. glycerol at an inlet flow rate of 1×10-8 m3/s, obtained with the compromise of pressure drops of 161 Pa and 203 Pa, respectively. A much lower mixing degree, of only 0.43, was registered at the same flow rate for the solution with 35% wt. glycerol, at a higher pressure drop of 316 Pa.
The optimum design of corrugated wavy channels used in mini-channel/micro-channel heat sink applications for minimum pumping power (i.e., minimum pressure drop) and efficient heat transfer is a great challenge in terms of energy savings point of view. In this paper, a commercial solver based on the Finite Element Method (FEM) was used for developing a two dimensional numerical model for a sine-shaped corrugated channel. The effect of channel geometry(spacing ratio ε and waviness parameter γ) on the friction coefficient f, average Nusselt number Nuav, pumping power P.P. and goodness factor G has been carried out for various numerical models at different Reynolds numbers between 100 and 1339. The Nuav parameter clearly increased at Re < 500 with the increasing of γ from 0.024 to 0.21, but with the expense of a higher friction factor.
In this paper we performed an experimental study of a Proton Exchange Membrane Fuel Cell (PEMFC) unit cell having single serpentine type channels for laminar flow of air at cathode and hydrogen at anode using a BEKKTECH BT-552 PEM fuel cell station (USA). Measurements have been collected at two different cathode backpressures of 20 kPa and 50 kPa, for the same anodic backpressure of 400 kPa at an operating temperature of 80°C. Humidified volumetric flow rates of H2 and air were maintained at 200 sccm and 800 sccm, respectively, with the help of two mass flow controllers. Cell voltage variations of current density loads between 50 mA/cm2 and 1000 mA/cm2 revealed the air stoichiometry point at which voltage oscillations dropped to negative values, due to air starvation. Another measurements of the PEMFC system voltage, at a constant load of 500 mA/cm2 and an air stoichiometry of 3.9 indicated non-uniform oscillations of the cell voltage for a cathodic backpressure of 50 kPa, with maximum peak-to-peak amplitudes ten times bigger than those registered in the case of the test at 20 kPa.
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