A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

Reaction rates in turbulent, reacting flows are reviewed. Assumed probability density functions (pdf) modeling of reaction rates is being investigated in relation to a three variable pdf employing a 'most likely pdf' model. Chemical kinetic mechanisms treating hydrogen air combustion is studied. Perfectly stirred reactor modeling of flame stabilizing recirculation regions was used to investigate the stable flame regions for silane, hydrogen, methane, and propane, and for certain mixtures thereof. It is concluded that in general, silane can be counted upon to stabilize flames only when the overall fuel air ratio is close to or greater than unity. For lean flames, silane may tend to destabilize the flame. Other factors favoring stable flames are high initial reactant temperatures and system pressure

Cultivo heterotrófico do camarão marinho Litopenaeus vannamei avaliando duas metodologias de remoção de sólidos

TCC (graduação em Engenharia de Aquicultura) - Universidade Federal de Santa Catarina, Centro de Ciências Agrárias, 2011O sistema heterotrófico é uma tecnologia que vem sendo desenvolvida a fim de se tornar uma alternativa aos cultivos tradicionais do camarão marinho Litopenaeus vannamei. Para manejá-lo se faz necessária a retirada periódica de sólidos da água, os quais não foram consumidos pelos camarões e ficam em excesso no tanque, podendo causar diversos problemas. Este experimento foi realizado com intuito de comparar índices de qualidade de água, volume de efluentes e desempenho zootécnico dos camarões em tanques com retirada de sólidos por decantadores (tratamento IB) e por renovação parcial (tratamento IR). Unidades experimentais consistiram em tanques circulares de 50 m2 de fundo e volume de trabalho igual a 48 m3, em triplicata, onde as unidades do tratamento IB apresentavam um decantador circular de 700 Litros acoplado lateralmente em cada tanque de cultivo. A densidade inicial foi de 164 cam/m2, sendo que estes apresentavam peso médio de 0,67 g. Os índices de qualidade de água não tiveram diferença significativa entre os tratamentos (p>0,05). No tratamento IB os sólidos foram manejados de maneira mais fácil e continua. Este gerou menos efluentes com valores de 8,85 L/kg camarão produzido e 7,25 L/kg de ração utilizada, contra 162,58 L/kg camarão e 97,12 L/kg ração em IR (p<0,05), e apresentou melhor desempenho zootécnico com peso final de 12,76 g, contra 10,16 g em 61 dias de experimento, com ganho de peso semanal de 1,44 g contra 1,15 g (p<0,05). O manejo dos sólidos suspensos totais e dos sólidos sedimentáveis foi possível nos dois tratamentos. Entretanto o cultivo sem troca de água, com retirada de sólidos por sedimentação em um decantador acoplado ao tanque, apresentou um grande potencial de aplicação. Isso porque nestas condições experimentais, foram obtidos animais maiores e produtividades mais elevadas, com menor gasto de água e melhor facilidade de manejo

CARS Spectral Fitting with Multiple Resonant Species using Sparse Libraries

The dual pump CARS technique is often used in the study of turbulent flames. Fast and accurate algorithms are needed for fitting dual-pump CARS spectra for temperature and multiple chemical species. This paper describes the development of such an algorithm. The algorithm employs sparse libraries, whose size grows much more slowly with number of species than a conventional library. The method was demonstrated by fitting synthetic "experimental" spectra containing 4 resonant species (N2, O2, H2 and CO2), both with noise and without it, and by fitting experimental spectra from a H2-air flame produced by a Hencken burner. In both studies, weighted least squares fitting of signal, as opposed to least squares fitting signal or square-root signal, was shown to produce the least random error and minimize bias error in the fitted parameters

Development of a Dual-Pump CARS System for Measurements in a Supersonic Combusting Free Jet

This work describes the development of a dual-pump CARS system for simultaneous measurements of temperature and absolute mole fraction of N2, O2 and H2 in a laboratory scale supersonic combusting free jet. Changes to the experimental set-up and the data analysis to improve the quality of the measurements in this turbulent, high-temperature reacting flow are described. The accuracy and precision of the instrument have been determined using data collected in a Hencken burner flame. For temperature above 800 K, errors in absolute mole fraction are within 1.5, 0.5, and 1% of the total composition for N2, O2 and H2, respectively. Estimated standard deviations based on 500 single shots are between 10 and 65 K for the temperature, between 0.5 and 1.7% of the total composition for O2, and between 1.5 and 3.4% for N2. The standard deviation of H2 is ~10% of the average measured mole fraction. Results obtained in the jet with and without combustion are illustrated, and the capabilities and limitations of the dual-pump CARS instrument discussed

An Experimental and Numerical Study of a Supersonic Burner for CFD Model Development

A laboratory scale supersonic burner has been developed for validation of computational fluid dynamics models. Detailed numerical simulations were performed for the flow inside the combustor, and coupled with finite element thermal analysis to obtain more accurate outflow conditions. A database of nozzle exit profiles for a wide range of conditions of interest was generated to be used as boundary conditions for simulation of the external jet, or for validation of non-intrusive measurement techniques. A set of experiments was performed to validate the numerical results. In particular, temperature measurements obtained by using an infrared camera show that the computed heat transfer was larger than the measured value. Relaminarization in the convergent part of the nozzle was found to be responsible for this discrepancy, and further numerical simulations sustained this conclusion

Beam Shaping for CARS Measurements in Turbulent Environments

This paper describes a new technique to mitigate the effect of beam steering on CARS measurements in turbulent, variable density environments. The new approach combines Planar BOXCARS phase-matching with elliptical shaping of one of the beams to generate a signal insensitive to beam steering, while keeping the same spatial resolution. Numerical and experimental results are provided to demonstrate the effectiveness of this approach. One set of experiments investigated the effect of beam shaping in the presence of a controlled and well quantified displacement of the beams at the focal plane. Another set of experiments, more qualitative, proved the effectiveness of the technique in the presence of severe beam steering due to turbulence

The Isolation, Differentiation, and Survival In Vivo of Multipotent Cells from the Postnatal Rat filum terminale

Neural stem cells (NSCs) are undifferentiated cells in the central nervous system (CNS) that are capable of self-renewal and can be induced to differentiate into neurons and glia. Current sources of mammalian NSCs are confined to regions of the CNS that are critical to normal function and surgically difficult to access, which limits their therapeutic potential in human disease. We have found that the filum terminale (FT), a previously unexplored, expendable, and easily accessible tissue at the caudal end of the spinal cord, is a source of multipotent cells in postnatal rats and humans. In this study, we used a rat model to isolate and characterize the potential of these cells. Neurospheres derived from the rat FT are amenable to in vitro expansion in the presence of a combination of growth factors. These proliferating, FT-derived cells formed neurospheres that could be induced to differentiate into neural progenitor cells, neurons, astrocytes, and oligodendrocytes by exposure to serum and/or adhesive substrates. Through directed differentiation using sonic hedgehog and retinoic acid in combination with various neurotrophic factors, FT-derived neurospheres generated motor neurons that were capable of forming neuromuscular junctions in vitro. In addition, FT-derived progenitors that were injected into chick embryos survived and could differentiate into both neurons and glia in vivo

Simultaneous Temperature and Velocity Measurements in a Large-Scale, Supersonic, Heated Jet

Two laser-based measurement techniques have been used to characterize an axisymmetric, combustion-heated supersonic jet issuing into static room air. The dual-pump coherent anti-Stokes Raman spectroscopy (CARS) measurement technique measured temperature and concentration while the interferometric Rayleigh scattering (IRS) method simultaneously measured two components of velocity. This paper reports a preliminary analysis of CARS-IRS temperature and velocity measurements from selected measurement locations. The temperature measurements show that the temperature along the jet axis remains constant while dropping off radially. The velocity measurements show that the nozzle exit velocity fluctuations are about 3% of the maximum velocity in the flow