Drag reduction in dilute fibre suspensions: Some mechanistic aspects

Long hair-like fibres were injected at the boundary and centreline of a turbulent pipe flow of water and polymeric solution. Pressure drop and mean velocity profiles were measured at various Reynolds numbers and injection rates in order to study some mechanistic aspects of drag reduction in these additive systems. Drag reduction in a fibre-water system is attributed to a decrease in the momentum transfer in the turbulent-core region, whereas synergism has been found to be a wall phenomenon.     

LAMINAR FILM BOILING ON A VERTICAL SURFACE WITH THERMAL LEAKAGE AT ITS ENDS

The analysis presented is for laminar film boiling on a vertical surface treating the test section as a fin with the heat leakage from its ends. The formulation of the problem is accomplished as a conjugate between the thermal conduction in the test section and the phenomenon of film boiling on its lateral face. This approach revealed that the film boiling heat transfer coefficients, both local and average values, are profoundly influenced by the fin parameter. An explicit form of the equation is provided from the computer results to evaluate the film boiling heat transfer coefficient.     

Catalytic oxidation of toluene and m-xylene by activated carbon fiber impregnated with transition metals

The catalytic oxidation of volatile organic compounds (VOCs) into mainly CO₂ and H₂O appears promising in the context of the abatement of atmospheric gaseous pollutants and is the subject of this paper. The catalytic oxidation of toluene and m-xylene was carried out in a tubular reactor on a phenolic resin based activated carbon fiber (ACF) impregnated with nitrates of Co, Cr, Ni, and Cu at the reaction temperatures below 300 °C. The extent of the removal (i.e. conversion) of toluene and m-xylene was examined through the breakthrough curves and was found to strongly depend on the types and loading of the metal precursors. The experimental results showed that the reaction rate was significantly affected by O₂ concentration below 3% (v/v). The performance of the ACFs impregnated with 5% (w/w) of Ni oxide was found to be superior to that of other metal oxides at reaction temperature between 170 and 290 °C. A surface kinetic mechanism for the catalytic oxidation of volatile organic compound was proposed and incorporated in a transport model developed to explain the experimental breakthrough data.     

Conductivity of molten hydrated salts: Mg(NO3)2. 6H2O + NH4NO3 system

Conductivity of molten Mg(NO₃)₂. 6H₂O + NH₄NO₃ system containing up to 80 mole percent of the latter was measured in the temperature range 320–400 K. Temperature dependence of conductivity exhibited Arrhenian behaviour. Conductivity—composition isotherms were non-linear indicating weak ordering tendencies. Equivalent conductivity data did not obey Markov equation; deviations have been interpreted in terms of the Tobolsky parameter (θ). Constancy of θ indicate that the water of hydration in the system remains with Mg²⁺ ions and is unaffected by the addition of NH⁺₄ ions.     

Low-Temperature Synthesis of Calcium Hexa-Aluminate

Calcium hexa-aluminate (CaO·6Al₂O₃) has been prepared from calcium nitrate and aluminum sulfate solutions in the temperature range of 1000°–1400°C. A 0.3 mol/L solution of aluminum sulfate was prepared, and calcium nitrate was dissolved in it in a ratio that produced 6 mol of Al₂(SO₄)₃·16H₂O for each mole of Ca(NO₃)₂·4H₂O. It was dried over a hot magnetic stirrer at ∼70°C and fired at 1000°–1400°C for 30–360 min. The phases formed were determined by XRD. It was observed that CaO·Al₂O₃ and CaO·2Al₂O₃ were also formed as reaction intermediates in the reaction mix of CaO·6Al₂O₃. The kinetics of the formation of CaO·6Al₂O₃ have been studied using the phase-boundary-controlled equation 1 − (1 − x )^1/3= K log t and the Arrhenius plot. The activation energy for the low-temperature synthesis of CaO·6Al₂O₃ was 40 kJ/mol.     

Synthesis and characterization of graft copolymers of hydroxypropyl cellulose with acrylamide and some comonomers

To obtain new polymeric materials for environmental management, we used pine needles from the huge forest of the Western Himalayas as a source of cellulose. Cellulose was derivatized to hydroxypropyl cellulose (HPC), a useful water‐soluble cellulose ether. HPC was graft‐copolymerized with acrylamide (AAm) with benzoyl peroxide as the initiator. At optimum grafting conditions, five different concentrations of the comonomers glycidyl methacrylate, acrylic acid, 2‐hydroxyethyl methacrylate, and acrylonitrile were grafted with AAm. Networks of HPC and AAm were also synthesized by crosslinking reactions with glutaraldehyde as a crosslinker over a range of four different concentrations of crosslinker under acidic conditions. Crosslinked networks of HPC with AAm and a comonomer at one comonomer concentration were also synthesized. Graft copolymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and swelling behavior. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 545–555, 2004     

Enzyme-assisted aqueous extraction of peanut oil

Enzyme-assisted aqueous extraction of oil from oilseeds is a relatively recent technique. In the present study, peanut oil was extracted under optimized aqueous extraction conditions using Protizyme^™, which is predominantly a mixture of acid, neutral, and alkaline proteases. The optimal conditions were: enzyme concentration of 2.5% (w/w) in 10 g of peanut seeds, pH 4.0, 40°C, and 18 h incubation with constant shaking at 80 rpm. Centrifuging the mixture at 18,000 × g for 20 min separated the oil with a recovery of 86–92%. The merits of this process over existing solvent extraction and/or mechanical pressing methods are discussed.     

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

In a multistrand,the outlet near the inlet produces short circuiting flow.This leads to the formation of dead zones inside the tundish,and consequently,the mean residence time decreases.In the present study,numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model.To decrease the dead zone volume inside the tundish,the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied.The outlets near the inlet were closed for varying amount of time,and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish,namely,mean residence time and the ratio of mixed to dead volume of the tundish.An optimum closure time of the near outlet has been found,which yields best mixing inside the tundish.The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution (RTD)curves.The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish.The educational version of computational fluid dynamics(CFD)soft ware PHOENICS was used to solve the governing equations and interpret the results in different forms.     

A systematic investigation of the integrated effects of gate underlapping,dual work functionality and hetero gate dielectric for improved performance of CP TFETs

This paper presents a comparative analysis of the combined effects of gate underlapping and dual work functionality with hetero gate dielectric engineering for a charge plasma tunnel field-effect transistor (CP TFET). Ultrathin nanoscale devices, despite their size and cost advantage, present serious issues, including doping control, random dopant fluctuation and fabrication complexity. Given these concerns, the concept of charge plasma is introduced to avoid the need for conventional doping for the formation of the source and drain regions, which makes the device resistive to process variation. Conduction for negative gate bias (ambipolarity), excess Miller capacitance (gate-to-drain capacitance) and poor RF performance in TFETs are addressed by the use of gate underlapping from the drain side. In addition, enhanced ON-state current is obtained by work function shifting (dual work functionality). This shift in work function can be accomplished by nitrogen doping of the gate electrode for experimental levels [1]. The combined effects of the underlap and dual work function are seen in the device having a single gate dielectric. However, the ON-state current remains lower in the case of \(\mathrm{SiO}_{2}\) as the gate dielectric. Therefore, a hetero gate dielectric \(\mathrm{SiO}_{2}\) on the drain side and \(\mathrm{HfO}_{2}\) on the source side are considered in order to improve the RF parameters and enhance the ON-current concept, respectively. Finally, the combined effects of gate underlap with work function shift and hetero dielectric are analyzed in CP TFETs. The results show that proper underlap length and gate work function provide a significant improvement in device performance. Therefore, optimization of the underlap length and work function is performed to determine the specific work function that provides overall enhancement of DC and analog/RF performance of the device. In addition, optimization of the dual work function gate length is demonstrated.