Fluidized bed combustor modeling

A general mathematical model for the prediction of performance of a fluidized bed coal combustor (FBC) is developed. The basic elements of the model consist of: (1) hydrodynamics of gas and solids in the combustor; (2) description of gas and solids contacting pattern; (3) kinetics of combustion; and (4) absorption of SO2 by limestone in the bed. The model is capable of calculating the combustion efficiency, axial bed temperature profile, carbon hold-up in the bed, oxygen and SO2 concentrations in the bubble and emulsion phases, sulfur retention efficiency and particulate carry over by elutriation. The effects of bed geometry, excess air, location of heat transfer coils in the bed, calcium to sulfur ratio in the feeds, etc. are examined. The calculated results are compared with experimental data. Agreement between the calculated results and the observed data are satisfactory in most cases. Recommendations to enhance the accuracy of prediction of the model are suggested

Distribution of rare earth elements in the Yamuna and the chambal rivers, India

We report here the first measurements of dissolved rare earth elements (REE) in the headwaters of the Yamuna river draining through the southern slopes of Himalaya. Due to intense weathering of the surface rocks of different lithologies and influence of tributaries, Yamuna river waters have variable dissolved REE contents (87 < ΣREE < 1374 ng L-1, mean = 288.6 ng L-1) and exhibit negative Eu anomaly (0.49 < Eu/Eu < 0.73, mean = 0.63). While most of the samples do not show discernable Ce anomalies; a negative Ce anomaly, however, found in a few of them, which can be explained by the colloidal pool preferentially enriched in Ce. A comparison among the river waters and bed sediments suggests that dissolved composition of REE is strongly fractionated and is enriched in MREE (Nd-Gd) with respect to sediments; presumably due to preferential dissolution of phosphate minerals such as apatite during weathering processes. Along with the Yamuna river, bed sediments from the Chambal river (a Peninsular river) have also been analyzed for REE composition. Bed sediments in the Yamuna and the Chambal river basins are characterized by ΣREE concentrations in the range of 78 to 291 µg g-1 (mean = 165 µg g-1) and 96 to 157 µg g-1 (mean = 134 µg g-1), respectively. A characteristic feature observed in the REE-normalized patterns of bed sediments is a strong HREE enrichment and a relatively positive Eu anomaly with respect to the granites in the Yamuna river catchment. In contrast, the bed sediment samples of the Chambal river show significant LREE enrichment and Eu enrichment with respect to the Deccan basalts in its catchment. The feldspars and their secondary products, which are enriched in Eu, might be the cause of the Eu anomaly. In river sediments of both these basins, the enrichment factors (EF), with respect to PAAS are ≤2 suggesting that REE composition is mainly derived from weathering processes

Guided Modes of Elliptical Metamaterial Waveguides

The propagation of guided electromagnetic waves in open elliptical metamaterial waveguide structures is investigated. The waveguide contains a negative-index media core, where the permittivity, $\epsilon$ and permeability $\mu$ are negative over a given bandwidth. The allowed mode spectrum for these structures is numerically calculated by solving a dispersion relation that is expressed in terms of Mathieu functions. By probing certain regions of parameter space, we find the possibility exists to have extremely localized waves that transmit along the surface of the waveguide

A search for a consistent model for the electromagnetic spectrum of the crab nebula

An attempt is made to search for a consistent model to explain the electromagnetic spectrum of the Crab nebula (Tau A). It is assumed that there is a continuous injection of electrons at the centre of the nebula with an energy spectrum E-1.54 as evidenced by radio data. This spectrum must steepen to a slope larger than 2 at some energy Ei in order to ensure that the energy input into electrons remains finite. The spectrum must also steepen beyond an energy Ec depending on the magnetic field because of synchrotron energy losses. Two types of models are considered: Class I, in which the whole nebula is characterised by a uniform magnetic field, and Class II, in which besides the general field H0, small filamentary regions of strong field Hs are postulated. In models of Class I, the best fit to the observed data is obtained when E t >E c and H0⋍5×10-4 gauss. However, this predicts a decrease in X-ray source size beyond ~40 KeV. There are two possibilities of Class II model depending on the residence time of electrons in strong field regions being small or large. The former case explains the flattening in the optical spectrum

Toxic effect of copper sulphate on protein alterations in esturine fish, Mugil cephalus

Heavy metals are common pollutants of estuarine ecosystems where they induce adverse effects on the aquatic biota. Copper is one of the most toxic heavy metal to fish and consumption of fish after copper treatment in water may pose a serious risk to human health. Fishes are generally used as pollution indicators in water quality management. Chronic effects include reduced growth, shorter lifespan, reproductive problems, reduced fertility and behavioral changes. Esturine fish, Mugil cephalus is an important fin fish species of Uppanar estury in Cuddalore region having good nutritional values. Fishes living in close association with the sediment may accumulate copper sulphate. In the present observation, the toxic effects of the copper sulphate LC50 35 μg/L (CuSO4) on (10% and 30%) two sublethal concentrations of total protein in gill, liver and muscles tissues of the esturine fish, Mugil cephalus were estimated during the periods of 5, 10 and 15 days exposure. There is decreased in all tissues on comparison with control. The results indicated the toxic nature of the heavy metal copper sulphate

Dust in a few southern H II regions

The property of dust in four southern H II region/molecular cloud complexes (RCW 108, RCW 57, RCW 122, and G351.6-1.3) was discussed. These regions were observed at an effective wavelength of 150 micron using TIFR balloon borne 1 m telescope and deconvolved maps with a resolution of 1 min were obtained. The data were combined with other available data to derive the properties of the infrared emitting dust in these regions

Distribution of dust in W31 complex

W31 is a H II region/molecular cloud complex in the galactic plane at a distance of 6 Kpc. This complex consists of two prominent radio continuum sources (G10.2-0.3 and G10.3-0.1) representing H II regions. An extended region covering both these H II regions was mapped in the Far IR (FIR) using the TIFR 1 m balloon-borne telescope with an angular resolution of approx. 1 min and a dynamic range of 100. The resulting flux density distribution at an effective wavelength of 160 microns is presented. The coadded IRAS survey scan data at 60 and 100 microns were deconvolved using a maximum entropy method to generate the flux density maps of the same region. These 60 and 100 micron maps are given and are briefly discussed

Far-infrared observations of Circinus and NGC 4945 galaxies

Circinus and NGC 4945 are two galaxies luminous in the infrared and are characterized by compact non thermal radio nuclei, deep silicate absorption features and unusually strong water vapor maser luminosities. Moorwood and Glass (1984) have observed these galaxies extensively in the 1 to 20 micron range. In the far-infrared, observations up to 100 microns are available from the Infrared Astronomy Satellite (IRAS). In order to study the cool dust component of these galaxies, researchers observed them at 150 microns using the Tata Institute of Fundamental Research (TIFR) 100 cm balloon-borne telescope. Here, they report observations along with deconvolved maps at 50 and 100 microns obtained from the Chopped Photometric Channel (CPC) on board IRAS

Mixing in the surface waters of the western Bay of Bengal using 228Ra and 226Ra

228Ra and 226Ra have been measured in the surface waters of the western Bay of Bengal during five cruises conducted between 1988 and 1999. The ranges and mean (given in brackets) concentrations for 228Ra and 226Ra are 6.8-42.1 (17.8 ± 7.9) dpm/100 kg and 6.0-16.7 (9.2 ± 2.2) dpm/ 100 kg, respectively. (228Ra/226Ra) Activity Ratio (henceforth denoted as [228/226]) ranges from 0.8 to 3.4 with a mean of 1.9 ± 0.5. Both 228Ra and 226Ra show inverse correlation with salinity, the former much stronger. A surface 2-D diffusion-advection model is used with a new approach. A simple bivariate function, C(x,y) = C0e-Ax·e-By where C0, A and B are constants, is fitted to the whole 228Ra and 226Ra data C(x,y). Substituting C(x,y) in the two-dimensional steady-state diffusion equation of Ra, the estimated values of the constants A and B can be related to eddy diffusivities and advection velocities in the zonal (x) and meridional (y) directions. From this relationship, the horizontal eddy diffusivities in the zonal and meridional directions are inferred to be 1.3 × 107 and 2.1 × 108 cm2s-1, respectively in the absence of advection terms. Similarly, neglecting the influence of diffusion, one can estimate the advection velocities, wx and wy in the zonal and meridional directions, as 0.2 and 1.1 cm s-1, respectively. The model-fit values C(x,y) of 228Ra concentrations are in good agreement with the measured values except in regions showing exceptionally high and low values. Incorporating both the advection rates and eddy diffusivities into the equation, it is found that increasing advection velocities depending on the direction can decrease or increase the eddy diffusivities and that such changes are more effective in the meridional direction compared to zonal direction in the region of study. On the whole, 228Ra appears a good tracer to derive rates of mixing between low salinity waters in the north and their high salinity southern counterparts of the western Bay of Bengal. The eddy diffusivities, Kx and Ky (without advection) derived for the Bay of Bengal are higher by about an order of magnitude than the ones similarly obtained for the Arabian Sea. This is not unexpected due to the turbulent conditions prevailing in the Bay of Bengal for most of the year

Mapping of Large Scale 158 micron [CII] Line Emission: Orion A

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 micron) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ~200 km/s and an angular resolution of 1.5'. During the first flight, an area of 30'x15' in Orion A was mapped. The observed [CII] intensity distribution has been compared with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and CO(3-2) from the literature. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV flux and volume density at a few selected positions.Comment: To appear in Astronomy & Astrophysic