Sleem ur Rahman

Natural convection along vertical wavy surfaces: an experimental study

Abstract Natural convective mass transfer coefficients from vertical copper blocks with sinusoidal wavy surfaces of varying amplitude to wavelength ratios (a/λ) have been experimentally obtained. A limiting diffusion current technique based on cathodic reduction of cupric ions was used. The mass transfer performance was observed to decrease with an increasing a/λ ratio. The average Sherwood number can be predicted for a wavy surface with given a/λ by Sh=0.915 Ra 0.238 (1+a/λ) −0.8577 within the studied range of Rayleigh numbers.

Electrochemical reduction of carbon dioxide over CNT-Supported nanoscale copper electrocatalysts

This paper presents the experimental investigation of copper loaded carbon nanotubes (CNTs) electrocatalysts for the electrochemical reduction of carbon dioxide. The electrocatalysts were synthesized by homogeneous deposition precipitation method (HDP) using urea as precipitating agent. The prepared catalysts were characterized by TEM, SEM, XRD, XPS, BET, and FTIR for their morphology and structure. Characterization results confirm the deposition of Cu nanoparticles (3-60 nm) on CNTs. Linear sweep voltammetry (LSV) and chronoamperometry (CA) were used to investigate the activity of the as-prepared catalysts for the electrochemical reduction of carbon dioxide. The electrocatalysts reduced CO2 with high current density in the potential range 0∼-3V versus SCE (standard calomel electrode). Among all catalysts tested, 20 wt. % copper loaded CNTs showed maximum activity. Gas chromatograph with TCD was used to analyze liquid phase composition. The faradaic efficiency for methanol formation was estimated to be 38.5%.

Perfluorinated Ionomer-Boron Phosphate Composite Membranes for Polymer Electrolyte Membrane Fuel Cell Applications

Composite membranes have been prepared from perfluorinated ionomer (10 wt % PFSA-H + solution) and boron phosphate (BPO 4 ). The contents of solid BPO 4 in the composite membrane varied from 10 to 50 wt %. The conductivityof the composite membranes measured both at room temperature and at higher temperatures was found to increase with the incorporation of boron phosphate particles into PFSA ionomer. The highest conductivity of 6.2 × 10 - 2 S/cm was found for the composite membrane containing 50% BPO 4 at 120°C. The membranes were characterized by X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy, which confirmed the presence of solid BPO 4 into the membranes. The morphology of the membranes showed the even distribution of BPO 4 particles into the composite membranes. These membranes have a strong potential to be considered for use in direct methanol fuel cells.

Hydrogen highway: An overview

This article presents the status of the technology to conceptualize hydrogen as a fuel and fuel cell car and hydrogen fueling station i.e. hydrogen infrastructure. Hydrogen is the lightest and most abundant element in the universe and it is an energy carrier. It can be produced from several sources using various methods and delivered to the fueling station or even it can be produced at the fueling station. Electrolysis of water or reforming of hydrocarbons such as natural gas can produce hydrogen in a big plant or even at the fueling station. But when it is produced using renewable energy such as wind, solar, geothermal, or hydroelectric, it has zero emissions in well to wheel. Hydrogen powdered vehicles either burns hydrogen in an internal combustion engine, or reacts with oxygen in a fuel cell. Developing a chain of hydrogen-equipped fueling stations and other infrastructure along the city road or highway, which will allow hydrogen powered cars to travel, is basically the concept of hydrogen highway. More substantial delivery infrastructure for hydrogen will require the use of high-pressure compressors for gaseous hydrogen and liquefaction system for cryogenic hydrogen. Hydrogen can be transport by road via cylinders, tube trailers, cryogenic tankers, and in pipelines or can be produced onsite. Each of these delivery and production modes requires a significantly different fueling station design. While hydrogen dispensers are basically the same regardless of the delivery or production mode, but the compressed and liquid hydrogen fueled vehicles are completely different. These combinations of hydrogen delivery or production at the station, compressed or liquid hydrogen dispensing, and various components and integration alternatives make up the array of hydrogen fueling station design and visualize total hydrogen infrastructure. Today, all the major automobile manufacturers have one or more prototype hydrogen fuel cell cars in their lineup. Again the advent of onsite hydrogen production system and/or home hydrogen fueling stations can help with the present infrastructure shortcoming. Companies such as Honda, ITM Power and Hydrogenics have at least prototype home hydrogen production and pumps, that may be available soon.

Application of titanium dioxide (TiO 2) based photocatalytic nanomaterials in solar and hydrogen energy: A short review

Tremendous amount of research work is going on Titanium dioxide (TiO2) based materials. These materials have many useful applications in our scientific and daily life and it ranges from photovoltaics to photocatalysis to photo-electrochromics, sensors etc.. All these applications can be divided into two broad categories such as environmental (photocatalysis and sensing) and energy (photovoltaics, water splitting, photo-/electrochromics, and hydrogen storage). Synthesis of TiO2 nanoparticles with specific size and structural phase is crucial, for solar sell application. Monodispersed spherical colloids with minimum size variation (5% or less) is essential for the fabrication of photonic crystals. When sensitized with organic dyes or inorganic narrow band gap semiconductors, TiO2 can absorb light into the visible light region and convert solar energy into electrical energy for solar cell applications. TiO2 nanomaterials also have been widely studied for water splitting and hydrogen production due to their suitable electronic band structure given the redox potential of water. Again nanostructured TiO2 has extensively been studied for hydrogen storage with good storage capacity and easy releasing procedure. All these issues and related finding will be discussed in this review.

A simple model for turbulent boundary layer mass transfer on flat plate in parallel flow

Abstract A simple model for turbulent mass transfer from a flat plate valid for wider range of Schmidt numbers is proposed. Based on 1/ n power law velocity/concentration profiles and integral momentum/mass equations, the model reveals that λ c , a parameter in universal concentration profile, is a function of Sc . Through an empirical approach, it is given as λ c =8.55 Sc 0.37 . With this function, the model matches with experimental data up to Sc =108.

Methanol Permeation Through Proton Exchange Membranes of DMFCs

This chapter presents efforts and progress being made by researchers worldwide to develop membranes with low methanol permeability, without compromising on other qualities, such as high ionic conductivity, good chemical and thermal stability, and cost. Three approaches have been pursued —Nafion membranes modification, development of alternative membranes, and development of high activity anode catalysts or methanol-tolerant cathode catalysts. Success has been made in developing membranes with permeability values of 10–70 times lower than the pure Nafion membranes. Various techniques, both electrochemical and non-electrochemical, for measuring methanol permeation through the membranes are also discussed. It has been found that electrochemical techniques are more accurate. Potentiometric technique in particular has ease of reproducibility of results, and getting more data points.