Oscillatory flow and heat transfer characteristics in a pipe and a packed column

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995.Includes bibliographical references (leaves 147-152).Microfiche.xviii, 152 leaves, bound ill. 29 cmThe fluid flow and heat transfer characteristics in a pipe subjected to a periodically oscillatory and reversing flow have been investigated numerically and experimentally. An examination of the governing equations and boundary conditions shows that the governing similarity parameters for the oscillatory flow in a pipe of finite length are the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the pipe. An experimental study on the onset of turbulence found that the changes in the sign of the pressure gradient are directly responsible for the occurrence of instability in an oscillatory and reversing pipe flow. Friction coefficients of a fully developed laminar oscillating and reversing pipe flow were investigated analytically and experimentally. The numerical simulation of a sinusoidally oscillatory and reversing flow in a pipe of finite length shows that, at any instant of time, there exist three flow regimes in the pipe: an entrance regime, a fully developed regime, and an exit regime. Based on the numerical results, a correlation equation of the space-cycle averaged friction coefficient was obtained. For forced heat convection in an oscillatory flow, it was found that the Prandtl number is the additional similarity parameter, besides the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the heated pipe. The numerical results of the associated heat transfer problem reveal that annular effects also exist in the temperature profiles of an oscillatory flow at high kinetic Reynolds numbers near the entrance and exit locations of the pipe. The space-cycle averaged Nusselt numbers of air oscillating in a pipe heated at constant temperature and uniform heat flux were obtained based on either the numerical results or the experimental data. The related problem of pressure drop in an oscillatory flow through a woven-screen packed column has also been investigated experimentally

One-step polyol synthesis of Rh-on-Pd bimetallic nanodendrites and their electrocatalytic properties for ethanol oxidation in alkaline media

We report a new, facile and one-step polyol route for the synthesis of Rh-on-Pd bimetallic nanodendrites that are composed of Pd cores with Rh branches. Ethylene glycol is used as a reducing agent while hexadecyltrimethylammonium bromide (CTAB) is used as a structure-directing agent. The as-synthesized nanodendrites are characterized by transmission electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy. It is demonstrated that the morphology and number of Rh branches can be regulated by varying, respectively, the molar ratio of Pd to Rh precursors and the CTAB content. An intriguing finding is that CTAB not only directs the growth of Rh branches but also enables the formation of uniformly-shaped Pd cores. This effective one-step polyol synthesis can be ascribed to the different reduction kinetics between Pd and Rh ions resulting in the formation of Pd cores prior to the growth of the Rh branches. The electrocatalytic properties of the carbon supported Rh-on-Pd bimetallic nanodendrites as the catalyst for ethanol oxidation in alkaline media are investigated. Cyclic voltammetry results show that the Rh-on-Pd/C catalysts display a much higher CO2 selectivity than a Pd/C catalyst. In particular, the ratio of the forward to backward peak current density (j f/jb) of the Rh-on-Pd (3 : 1)/C catalyst is 2.2, which is three times that of the Pd/C catalyst. This journal is © 2013 The Royal Society of Chemistry

High-performance alkaline ionomer for alkaline exchange membrane fuel cells

An alkaline ionomer synthesized with a cross-linker, featured with long aliphatic chains of alkyl groups and inherent diamine structures, not only exhibits a high ionic conductivity (60.5 mS cm(-1)), but also significantly boosts the peak power density of H-2/O-2 alkaline exchange membrane fuel cells to 342 mW cm(-2). (C) 2013 Elsevier B.V. All rights reserved