The influence of the flame structure on the combustion oscillations in a cylindrical chamber

An experimental study has been conducted with the objective of investigating the effects of the flame structure in the combustion oscillation conditions into a laboratorial scale cylindrical chamber. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. To analyze the flame structure the image tomographic reconstruction process were used, and the resultant images were associated to the oscillatory conditions (frequency and amplitude) into the combustion chamber. The main conclusions were: 1) when the flame premixed condition increase, for example 60% of the total air flow rate is premixed with LPG, the region of intense energy released is close to burner exit and strong amplitudes of oscillation (close to 50 mbar) were obtained into the chamber; 2) for long flames, predominantly diffusive flames, just weak amplitudes were detected, in the spite of the speaker exiting the premixed flow; 3) when the energy is released distributed through the combustion chamber, the long flame acts like a baffle. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Determination of calcium and magnesium in hydroethanolic extracts of propolis by atomic absorption flame spectrophotometry

Propolis is a natural product collected by honeybees and has a large range of pharmacological activity, including antimicrobial, antitumoral, antioxidant and anti-inflammatory. Its use as a popular medicine is increasing all over the world, creating a need for quality control of the commercial products. In this study the levels of calcium and magnesium in commercial hydroalcoholic propolis extracts from varies states of Brazil were determined by atomic absorption flame spectrophotometry and different values were obtained for northern and southern states. This study can be extended to the analysis of metals that are harmful to health. The results showed that the calibration curves were linear over a wide concentration range (0.5-4.0 μg.mL -1 for calcium and 0.05-0.4 μg.mL -1 for magnesium) with good correlation coefficients (0.999 and 0.988, respectively). Good analytical recovery (94%) was obtained. The proposed method showed adequate precision and relative standard deviation lower than 2 %. The method is accurate and precise as well as having advantages such as simplicity and speed.

Determination of copper at wide range concentrations using instrumental features of high-resolution continuum source flame atomic absorption spectrometry

This work describes a method to determine Cu at wide range concentrations in a single run without need of further dilutions employing high-resolution continuum source flame atomic absorption spectrometry. Different atomic lines for Cu at 324. 754 nm, 327. 396 nm, 222. 570 nm, 249. 215 nm and 224. 426 nm were evaluated and main figures of merit established. Absorbance measurements at 324. 754 nm, 249. 215 nm and 224. 426 nm allows the determination of Cu in the 0. 07-5. 0 mg L -1, 5. 0-100 mg L -1 and 100-800 mg L -1 concentration intervals respectively with linear correlation coefficients better than 0. 998. Limits of detection were 21 μg L -1, 310 μg L -1 and 1400 μg L -1 for 324. 754 nm, 249. 215 nm and 224. 426 nm, respectively and relative standard deviations (n = 12) were ≤ 2. 7%. The proposed method was applied to water samples spiked with Cu and the results were in agreement at a 95% of confidence level (paired t-test) with those obtained by line-source flame atomic absorption spectrometry.

Sequential Determination of Cd, Cu and Pb in Tea Leaves by Slurry Introduction to Thermospray Flame Furnace Atomic Absorption Spectrometry

A simple procedure for the sequential determination of Cd, Cu and Pb in tea leaves by slurry introduction to thermospray flame furnace atomic absorption spectrometry was developed. Detection limits were 0.05 mg kg-1 for Cd, 2.1 mg kg-1 for Cu and 0.68 mg kg-1 for Pb using 0.67 % (m/v) slurries (100 mg/15 mL). © 2013 Springer Science+Business Media New York.

Evaluation of lines of boron, phosphorus and sulfur by high-resolution continuum source flame atomic absorption spectrometry for plant analysis

The wavelength-integrated absorbance (WIA) and summation of absorbance (∑ lines) of different lines were evaluated to enhance sensitivity and determine B, P and S in medicinal plants by HR-CS FAAS. The lowest LOD for B (0.5mgL-1) and P (13.7mgL-1) was obtained by integration of lines 249.773nm (3pixels) and 247.620nm (5pixels), respectively. The ∑ lines for CS at 257.595nm and 257.958nm furnished LOD=30.5mgL-1, ca. 10% lower than the LOD obtained for the WIA using 257.595nm and 5pixels. Data showed the advantage of WIA over ∑ lines to improve sensitivity for all analytes. Under optimized conditions, calibration curves in the 1.0-100mgL-1 B and 50.0-2000mgL-1 P, S ranges were consistently obtained. Results obtained with the HR-CS FAAS method were in agreement at 98% and 95% confidence level with certified values for B and P, respectively. And results for S were in accordance to non-certified values. Concentrations of B, P, and S in 12 medicinal plants analyzed by the proposed method varied within the 19.4-34.5mgkg-1 B, 719-3910mgkg-1 P and 1469-7653mgkg-1 S ranges. © 2012 Elsevier B.V.

Avaliação da disseminação de Salmonella Senftenberg isoladas de diversos ambientes avícolas utilizando a técnica de Pulsed Field Gel Electrophoresis

Pós-graduação em Microbiologia - IBILCE

Cross linked Poly (4-Vinylpyridine-Ethylene Glycol Dimethacrylate) Used for Preconcentration of Cd(II) and its Determination by Flow Injection Flame Atomic Absorption Spectrometry

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Flame retardant properties of the bark powder of Anadenanthera peregrina var. falcata (Benth.) Altschul (angico) studied by coupled thermogravimetry-Fourier transform infrared spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Application of pulsed Nd:YAG laser in thin foil microwelding

Experimental investigations were carried out using a Nd:YAG laser operating in pulsed mode for welding a lap joint between thin foil and thick sheet. The pulse energy was varied from 1.5 to 3.0 J at increments of 0.25 J with a 4 ms pulse duration. The base material used for this study was AISI 316L foils with 100 mu m thickness and sheet with 3.0 mm thickness. The welds were analysed by optical and electronic microscopy, tensile shear tests and micro hardness. The results indicate that pulse energy control is of considerable importance to join thin foil and thick sheet with good quality. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. The process appeared to be very sensitive to the gap between couples. Large voids delimited by the molten zone boundary were observed in joints welded with high pulse energy.

Effects of laser beam energy on the pulsed Nd:YAG laser welding of thin sheet corrosion resistant materials

The aim of this study was to value the possibility to join, for pulsed Nd:YAG laser welding, thin foils lap joints for sealing components in corrosive environment. Experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser weld to examine the influence of the pulse energy in the characteristics of the weld fillet. The pulse energy was varied from 1.0 to 2.5 J at increments of 0.25 J with a 4 ms pulse duration. The base materials used for this study were AISI 316L stainless steel and Ni-based alloys foils with 100 mu m thickness. The welds were analyzed by electronic and optical microscopy, tensile shear tests and micro hardness. The results indicate that pulse energy control is of considerable importance to thin foil weld quality because it can generate good mechanical properties and reduce discontinuities in weld joints. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. In all the specimens, fracture occurred in the top foil heat-affected zone next to the fusion line. The microhardness was almost uniform across the parent metal, HAZ and weld metal. A slight increase in the fusion zone and heat-affected zone compared to those measured in the base metal was observed. This is related to the microstructural refinement in the fusion zone, induced by rapid cooling of the laser welding. The process appeared to be very sensitive to the gap between couples.

Determination of furanic aldehydes in sugarcane bagasse by high-performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles

A glassy carbon electrode chemically modified with nickel nanoparticles coupled with reversed-phase chromatography with pulsed amperometric detection was used for the quantitative analysis of furanic aldehydes in a real sample of sugarcane bagasse hydrolysate. Chromatographic separation was carried out in isocratic conditions (acetonitrile/water, 1:9) with a flow rate of 1.0 mL/min, a detection potential of -50 mV vs. Pd, and the process was completed within 4 min. The analytical curves presented limits of detection of 4.0 × 10(-7) mol/L and 4.3 × 10(-7) mol/L, limits of quantification of 1.3 × 10(-6) and 1.4 × 10(-6) mol/L, amperometric sensitivities of 2.2 × 10(6) nA mol/L and 2.7 × 10(6) nA mol/L for furfural and 5-hydroxymethylfurfural, respectively. The values obtained in this sample by the standard addition method were 1.54 ± 0.02 g/kg for 5-hydroxymethylfurfural and 11.5 ± 0.2 g/kg for furfural. The results demonstrate that this new proposed method can be used for the quick detection of furanic aldehydes without the interference of other electroactive species, besides having other remarkable merits that include excellent peak resolution, analytical repeatability, sensitivity, and accuracy.