Modeling of hydro-thermo-mechanical behavior of Nafion NRE212 for Polymer Electrolyte Membrane Fuel Cells using the Finite Viscoplasticity Theory Based on Overstress for Polymers (FVBOP)

The primary aim of this work is to present the modifications made to the Finite Viscoplasticity Theory Based on Overstress for Polymers (FVBOP). This is a unified state variable theory and the proposed changes are designed to account for humidity and temperature effects relevant to the modeling of the hydrothermal deformation behavior of ionomer membranes used in Polymer Electrolyte Membrane Fuel Cells (PEMFC). Towards that end, the flow function, which is responsible for conferring rate dependency in FVBOP, is modified. A secondary objective of this work was to investigate the feasibility of using the storage modulus obtained by Dynamic Mechanical Analysis (DMA) in place of the elasticity modulus obtained from conventional tensile/compressive tests, and find the correlation between the storage modulus and the elasticity modulus. The numerical simulations were juxtaposed against data from tensile monotonic loading and unloading experiments on perfluorosulfonic acid (PFSA) membrane Nafion NRE212 samples which are used extensively as a membrane material in PEMFC. The deformation behavior was modeled at four different temperatures (298, 323, 338, and 353 K—all values below the glass transition temperature of Nafion) and at three water content levels (3, 7 and 8 % swelling). The effects of strain rate, temperature, and hydration were captured well with the modified FVBOP model.     

Effect of weight percentage and particle size of B4C reinforcement on physical and mechanical properties of powder metallurgy Al2024-B4C composites

In this study, Al2024-B₄C composites containing 0, 5, 10 and 20 wt% of B₄C particles with two different particle sizes (d₅₀=49 μm and d₅₀=5 μm) as reinforcement material were produced by a mechanical alloying method. Two new particle distribution models based on the size of reinforcement materials was developed. The microstructure of the Al2024-B₄C composites was investigated using a scanning electron microscope. The effects of reinforcement particle size and weight percentage (wt%) on the physical and mechanical properties of the Al2024-B₄C composites were determined by measuring the density, hardness and tensile strength values. The results showed that more homogenous dispersion of B₄C powders was obtained in the Al2024 matrix using the mechanical alloying technique according to the conventional powder metallurgy method. Measurement of the density and hardness properties of the composites showed that density values decreased and hardness values increased with an increase in the weight fraction of reinforcement. Moreover, it was found that the effect of reinforcement size and reinforcement content (wt%) on the homogeneous distribution of B₄C particles is as important as the effect of milling time.     

Natural convection in porous triangular enclosures with a solid adiabatic fin attached to the horizontal wall

A numerical analysis has been performed to investigate the effects of fin location onto the bottom wall of a triangular enclosure filled with porous media whose height base ratio is 1. The temperature of the bottom wall is higher than that of the inclined wall while the vertical wall is insulated. Thus, the fin divides the heated bottom wall to two separate regions. Finite difference method was applied to solve governing equations which are written using Darcy method. Solutions of algebraic equations were made by Successive Under Relaxation (SUR) technique. The effective parameters on flow and temperature fields are: Rayleigh number, location center of fin, dimensionless fin height, and dimensionless fin width. The obtained results indicated that the fin can be used as a control element for heat transfer and fluid flow.     

Rapid and slow pyrolysis of pistachio shell: effect of pyrolysis conditions on the product yields and characterization of the liquid product

This study reports the experimental results for the pyrolysis of pistachio shell under different conditions in a tubular reactor under a nitrogen flow. For the different conditions of pyrolysis temperature, nitrogen flow rate and heating rate, pyrolysis temperature of 773 K gave the highest bio-oil yield with a value of 27.7% when the heating rate and carrier gas flow rate were chosen as 300 K min⁻¹ and 100 cm³ min⁻¹, respectively. Column chromatography was applied to this bio-oil and its subfractions were characterized by elemental analysis, FT-IR and ¹H-NMR. Aliphatic subfraction was conducted to gas chromatography–mass spectroscopy for further characterization. The results for the characterization show that using pistachio shell as a renewable source to produce valuable liquid products is applicable via pyrolysis. Copyright © 2006 John Wiley & Sons, Ltd.     

The effects of Prandtl number on natural convection in triangular enclosures with localized heating from below

The effect of Prandtl number on natural convection heat transfer and fluid flow in triangular enclosures with localized heating has been analyzed by solving governing equations of natural convection in streamfunction–vorticity form with finite-difference technique. Solution of linear algebraic equations was made by Successive Under Relaxation (SUR) method. Bottom wall of triangle is heated partially while inclined wall is maintained at a lower uniform temperature than heated wall while remaining walls are insulated. Computations were carried out for dimensionless heater locations (0.15 ≤ s ≤ 0.95), dimensionless heater length (0.1 ≤ w ≤ 0.9), Prandtl number (0.01 ≤ Pr ≤ 15) and Rayleigh number (10³ ≤ Ra ≤ 10⁶). Aspect ratio of triangle was chosen as unity. It is observed that both flow and temperature fields are affected with the changing of Prandtl number, location of heater and length of heater as well as Rayleigh number.     

Experimental investigation of cooling of heated circular disc using inclined circular jet

An experimental study is performed to examine the heat transfer characteristics of impinging circular jet onto a heated circular disc. The disc is heated under constant heat flux and it has an inclination angle with impinging jet in the range of 90° ≤ φ ≤ 150°. The air is supplied using a radial fan. The fluid flows through a designed tunnel. Experiments were performed under different Reynolds number, 2800, 9000, and 36,000, and different values of inclination angle of the disk and jet-to-plate distance to jet diameter ratio H/D_h as 5, 10, and 15. The results of experiments showed that the most effective parameter is the inclination angle between jet and heater. Both locations of stagnation point and heat transfer are affected from this parameter.     

Simulating colliding flows in smoothed particle hydrodynamics with fractional derivatives

We propose a new method based on the use of fractional differentiation for improving the efficiency and realism of simulations based on smoothed particle hydrodynamics (SPH). SPH represents a popular particle‐based approach for fluid simulation and a high number of particles is typically needed for achieving high quality results. However, as the number of simulated particles increase, the speed of computation degrades accordingly. The proposed method employs fractional differentiation to improve the results obtained with SPH in a given resolution. The approach is based on the observation that effects requiring a high number of particles are most often produced from colliding flows, and therefore, when the modeling of this behavior is improved, higher quality results can be achieved without changing the number of particles being simulated. Our method can be employed to reduce the resolution without significant loss of quality, or to improve the quality of the simulation in the current chosen resolution. The advantages of our method are demonstrated with several quantitative evaluations. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of different drying methods on the essential oil yield,composition and antioxidant activity of <Emphasis Type="Italic">Origanum vulgare</Emphasis> L. and <Emphasis Type="Italic">Origanum onites</Emphasis> L.

Origanum onites and Origanum vulgare are important medicinal plants because of their flavoring, therapeutic, and preservative properties. Drying methods are important for obtaining high quality essential oil from spices. In this study, the effects of different drying processes on the essential oil yield, composition, and antiradical activity were evaluated. Plants were dried under sun light, in a ventilated shady place and in laboratory-type oven, and the oils were extracted with Clevenger type apparatus. Carvacrol and thymol were the major compounds in the essential oils of O. vulgare and O. onites, respectively. The highest oil yield and the highest antioxidant activity values were obtained from shade dried Origanum species followed by oven dried plants. The lowest essential oil yield and the lowest antioxidant activity for O. vulgare were found in fresh plants. The lowest essential oil yield, and the lowest antioxidant activity for O. onites belonged to sun dried plants. It could be concluded that essential oil yield, oil composition and antioxidant activity of both plants were greatly affected by the drying method.