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  • Effects of Flow Pulsing on Passive Scalar Mixing in a Turbulent Round Jet
  • Abstract This work presents a study on the effect of pulsing on a jet flow. Pulsing is used to modify jet inlet conditions with the objective of improving mixing. In this experimental work, a jet was slightly heated so that temperature could be considered as a passive scalar. The spectral behaviour of velocity and the passive scalar temperature was analyzed along the jet axis with and without pulsing. Low frequency pulsing (f/fS< 0.05 fSthe Strouhal frequency) modifies the spectral composition of the velocity at the jet exit, but it does not affect the asymptotic profile reached in the fully developed region…
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  • Development of a Hyperbranched Fuel Cell Membrane Material for Improved Proton Conductivity
  • Abstract A new material for proton conducting membrane with a higher proton transport but reduced water transport is being developed. The new material optimizes proton channel formation, this reducing water transport at the same time. Different proton transporting groups along with different gas flowing channels are examined as well. To meet the goals we design, synthesize, and simulate various proton transporting groups using MD techniques for faster optimization, which in turn helps to synthesize and test only promising structures in the laboratory. At the same time, computer modeling is used to improve the fuel cell system at various operating conditions, specifically…
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  • Characterization of Undoped Spray-Deposited ZnO Thin Films of Photovoltaic Applications
  • Abstract Undoped polycrystalline ZnO thin films were produced on glass substrates at a substrate temperature Ts= 450 C by the spray pyrolysis (SP) technique. The films were characterized by analyzing their I-V curves, transmittance, X-ray diffractograms (XRD) and their scanning electron microscope (SEM) images. The I-V plots are all linear and the resistivity was found to be about 200W.cm. The transmittance in the visible and near infrared regions is as high as 85% which is suitable for solar cell applications. The absorption coefficient which is deduced from the transmittance measurements is continuously increasing with the photon's energy and it rapidly increases…
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  • Arrangement of Monomer Injection in the Characteristics of Copolymer
  • Abstract Polypyrrole/Poly(vinyl acetate) (PPy/PVAc) copolymer was prepared by the copolymerization of vinyl acetate and pyrrole using FeCl3and benzoylperoxide as an oxidant in the presence of various surfactants such as sodium dodecylbenzenesulfonate and poly(ethylene glycol) in the aqueous/non-aqueous media. The PPy/PVAc copolymer was characterized in terms of conductivity, morphology, chemical structure, particle size and yield. The results indicate that the morphology, particle size, yield and electrical conductivity of the products are dependent on the type of surfactant and the arrangement of monomer injection. The chemical structure of obtained product was determined by FTIR spectroscopy. By comparison FTIR spectra between pure PPy and…
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  • A Comparative Study of Phase Changing Characteristics of Granular Phase Change Materials Using DSC and T-History Methods
  • Abstract In the present article, differential scanning calorimetry (DSC) and a modified T-history method have been used to study the phase changing behavior of granular composites. Further modifications and improvements of the two methods are employed to handle granular materials undergoing phase change over a temperature range. A simple procedure has been advised to obtain accurate results from the DSC measurements based on the estimation of the thermal resistance between the sample and its enclosure. The concept of enthalpy and its relationship with temperature has been employed in the T-history analysis to obtain enthalpy-temperature and apparent heat capacity curves similar to…
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  • Effect of Confined and Heated Ambient Air on Onset of Instability in Liquid Bridges of High Pr Fluids
  • Abstract The present work reports about an experimental study investigating the influence of air convection and of ambient temperature around a half-floating zone on the transition behavior from steady to oscillatory flow, i.e. the influence on the critical Marangoni number (Macr). Increase of heat loss from the free surface of the half-floating zone or liquid bridge by increased convection and ambient cooling decreases Macr. Heat input to the free surface increases Macr. An add-on numerical simulation of the air convection around the zone clarifies the influence of air convection and the ambient temperature on the temperature, surface velocity and local Biot…
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  • Effect of Ambient-Gas Forced Flow on Oscillatory Thermocapillary Convection of Half-Zone Liquid Bridge
  • Abstract The authors focus on thermocapillary-driven flow in a half-zone liquid bridge and its transition from two-dimensional steady flow to three-dimensional oscillatory one under an effect of forced convection in ambient gas region around the liquid bridge. The liquid bridge is settled in a cylindrical 'external shield,' in which upward/downward forced flow of the ambient gas is added. The critical condition of the flow transition in the 2-cSt silicone-oil liquid bridge is examined as functions of the aspect ratio and the volume ratio of the liquid bridge, and averaged velocity of the ambient gas. The authors indicate a significant effect of…
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  • On Flows Driven by Mechanical Stresses in a Two-Phase System
  • Abstract Gas-liquid flows in annulus are analyzed for fluids in large range of viscosity ratios. The geometry corresponds to a liquid bridge co-axially placed into an outer cylinder with solid walls. The internal core consists of solid rods at the bottom and top, while the central part is a relatively short liquid zone filled with viscous liquid and kept in its position by surface tension. The gas enters into the annular duct and entrains initially quiescent liquid. The flow structures in the liquid and gas are obtained numerically for different shapes of solid rods. Solution for fully developed flow in annulus…
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  • Thermocapillary and Natural Convection in Double Layer Systems of Herschel-Bulkley and Newtonian Fluids, Exact Solutions
  • Abstract A variety of exact analytical solutions describing natural and thermocapillary convection in a horizontal double layer system consisting of Newtonian and Herschel-Bulkley fluids subjected to longitudinal temperature and concentration gradients is constructed. The lower boundary of the system is a solid wall with no-slip, while the upper ones if either a solid wall or a free surface. It was demonstrated that, depending on the governing parameters of the system, viscoplastic layer is entirely yielded or unyielded, or it can be yielded partially, exhibiting up to 5 flowing and quasi-solid layers. The dependence of the flow patterns (appearance and position of…
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  • Rayleigh-Marangoni Instability of Binary Fluids with Small Lewis Number and Nano-Fluids in the Presence of the Soret Effect
  • Abstract A general model for two-component transport phenomena applicable for both nanofluids and binary solutions is formulated. We investigate a combined long-wave Marangoni and Rayleigh instability of a quiescent state of a binary (nano-) liquid layer with a non-deformable free surface. The layer is heated from below or from above. The concentration gradient is induced due to the Soret effect. A typical behavior of monotonic and oscillatory instability boundaries is examined in the limit of asymptotically small Lewis numbers and poorly conducting boundaries in the two important long-wave domains k~Bi1/2and k~Bi1/4.
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Displaying 6761-6770 on page 677 of 7662. Per Page