Pressure Drop Studies on Flow of Viscoelastic Fluid Through a Packed Bed

In the present study, pressure drop-flow rate behavior for the flow of viscoelastic fluid through porous media has been investigated. Aqueous solutions of polyacrylamide (PAM) and water in the concentration range of 0.02 to 0.1% wt/vol were used to elucidate the effect of fluid elasticity on bed pressure drop. Based on the observed data, the existing pore model was extended to predict the bed pressure drop for viscoelastic fluid flowing through a porous media. A statistical comparison between the existing models and the present model was made. The proposed correlation based on modified pore model predicts the data well to within a reasonable accuracy of ±10% with arithmetic relative error (%ARE) and mean relative quadratic error (MRQE) of 8.3% and 0.122, respectively.     

Dielectric relaxation studies on [PEO–SiO<Subscript>2</Subscript>]:NH<Subscript>4</Subscript>SCN nanocomposite polymer electrolyte films

Present work deals with findings on dielectric relaxation behaviour and a.c. conduction in a SiO₂-doped polymer nanocomposite electrolyte system, namely, [(100 − x)PEO + xSiO₂]:yNH₄SCN. The formation of nanocomposite has been ascertained by XRD measurements. The effect of salt and filler (SiO₂) on conductivity response of PEO-based nanocomposite polymer electrolyte has been investigated by impedance spectroscopy. The variation of dielectric permittivity, dielectric loss and modulus spectra with frequency and temperature was carried out from impedance spectroscopy data. The a.c. conductivity seems to follow the universal power law.     

Attenuation of ultrasonic waves in V, Nb and Ta at low temperatures

Variation of ultrasonic attenuation and velocities with temperature have been evaluated in the temperature range 5-50 K due to electron-phonon interaction mechanism in transition metals vanadium, niobium and tantalum for longitudinal and shear waves. For this evaluation, we have also computed the second order elastic constants using Morse potential. Behaviour of acoustical phonons in these bcc metals is different from other normal metals, intermetallics, semimetallics and alloys. Some characteristic features of these materials connected to ultrasonic parameters are discussed.     

Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product

BACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium. RESULTS: Among the isolates, a bacterial strain (CSB‐4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L^?1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH ～7.0, 100 mg L^?1 Cr(VI), 35 °C temperature and stirring speed 100 rpm, CSB‐4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 × 10^?2 to 6.5 × 10^?3 h^?1 for Cr(VI) concentration of 10–500 mg L^?1. The activation energy derived from temperature dependence rate constants between 25 and 35 °C was found to be 99 kJ mol^?1. The characterization of reduced product associated with bacterial cells by SEM‐EDS, FT‐IR and XRD was also reported. CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB‐4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. Copyright © 2010 Society of Chemical Industry     

Green biomass active electronic diode

For the first time, a biomass electronic junction functioning as a conventional electronic diode inside green leaves of Vinka-rosa and Plumeria rubra mass structure has been experimentally predicted and studied. The experimental diode demonstrated appropriate conventional electronic diode characteristics. The predicted diode junctions were operated for forward and reverse dc voltage biases in the range of ±1 to 10 and 1 to 30?V respectively. The studies revealed a strong functional dependence on the water content of the green leaf. These studies are sequential to the very recently reported research work of Kosta et al. on bioelectronics and soilelectronics. The study speculatively forecasts the beginning of a new revolutionary era of green biomass electronic circuitry.     

Size dependence of martensite transformation temperature in nanostructured Ni-Mn-Sn ferromagnetic shape memory alloy thin films

In the present study, we report the influence of grain size on structural and phase transformation behaviour of nanostructured Ni-Mn-Sn ferromagnetic shape memory alloy thin films synthesized by dc magnetron sputtering. With increase in substrate temperature, the structural phase changes from austenite with L2₁ cubic crystal structure to martensite with monoclinic structure. In addition, field-induced martensite-austenite transformation is observed in magnetization studies using superconducting quantum interference device magnetometer. The martensitic transformation behaviour of these films depends critically on the microstructure and dimensional constraint. Both, the martensite start temperature (M_s) and austenite finish temperature (A_f) of these nanostructured films decreases with decreasing grain size. The excess free volume associated with grain boundaries has been observed to increase with decrease in grain size which in turn leads to an increase in the number of grain boundaries. It has been proposed that the grain boundaries impose constraints on the growth of the martensite and confine the transformed volume fraction in nanocrystalline structure. A martensite phase nucleated within a grain will be stopped at the grain boundaries acting as obstacles for martensite growth. The investigations revealed that below a critical grain size of 10.8 nm, the austenite phase is observed to be more stable than the martensite phase which leads to the complete suppression of martensitic transformation in these films.     

Monthly Rainfall Prediction Using Wavelet Neural Network Analysis

Rainfall is one of the most significant parameters in a hydrological model. Several models have been developed to analyze and predict the rainfall forecast. In recent years, wavelet techniques have been widely applied to various water resources research because of their time-frequency representation. In this paper an attempt has been made to find an alternative method for rainfall prediction by combining the wavelet technique with Artificial Neural Network (ANN). The wavelet and ANN models have been applied to monthly rainfall data of Darjeeling rain gauge station. The calibration and validation performance of the models is evaluated with appropriate statistical methods. The results of monthly rainfall series modeling indicate that the performances of wavelet neural network models are more effective than the ANN models.     

Analysis of startup oscillations in natural circulation boiling systems

The aim of the present work is to get an insight of the phenomena behind the low-pressure low-power transients that occur during startup of a natural circulation boiling system. A RELAP5 model developed for a test facility and its prototype is used to record additional system parameters that were not included in the data obtained from experiments. The flow oscillations observed during experimental and numerical studies are analyzed and classified. It is inferred that the low amplitude oscillations are not condensation induced geysering instabilities, but a density wave instability supported by flashing. The similarity between the nature of startup transients observed in the test facility and the prototype is also examined. The effect of flashing is more pronounced in the prototype due to the strong variation of saturation temperature as the length scale is 4 times that of the model. The time series data obtained from experimental observations and numerical simulations are analyzed to identify the structural nature of flow oscillations. The power spectral density estimated using fast Fourier transform (FFT) algorithm illustrates the chaotic nature of the signals. The nonlinear time series analysis (TISEAN) package has been used for the estimation of Lyapunov exponent and the Poincaré section. The Poincaré section and the Lyapunov exponent confirm the chaotic nature of the flow oscillations.