Scielo RSS <![CDATA[Latin American applied research]]> vol. 34 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Numerical simulation of flow in a hydrocyclone]]> A new method is presented to predict the localization of an air core, which is usually found on the internal flow of hydrocyclones. The control and stability of the air core affect the flow split between the products of a hydrocyclone. The flow split is one of the least understood aspects of the hydrocyclone operation. This split is greatly influenced by the air core radius, so an understanding of the air core behavior would enhance the prediction of the flow split. The liquid-air interface is characterized by means of the Young-Laplace jump condition. A steady flow of Newtonian fluid is being considered. It was developed a model considering the air core as having a cylindrical shape. This model that we are presenting considers a radius as optimum, when the final expression for the jump condition of the interface liquid - air is minimum. With the velocity field obtained for an optimal air core radius, we can trace the trajectories of the solid particles, thus, it is possible to simulate the performance of the hydrocyclone. The velocity field, the flow split and the selectivity curve obtained are compared to experimental results. Good concordance is achieved. <![CDATA[Catalytic wet oxidation of ethanol in an integral trickle-bed reactor operated with liquid flow modulation]]> The effect of liquid flow modulation on the performance of an integral trickle-bed reactor used for carrying out the catalytic wet oxidation of ethanol is analyzed. Particular emphasis is devoted to examine whether the induced periodic variations in conversion are affected by prolonged operation. A Pt/γ-Al2O3 catalyst (1% w/w, mean particle diameter dp = 0.003 m) is employed for the experiments. Liquid flow is open/closed periodically by means of a programmable logic controller with given splits and at different total cycle period. The reactor operates isothermally at 70ÂșC during the whole cycles. The time dependence of the outlet ethanol concentration in the integral TBR is examined. In addition, the average conversion obtained with periodic operation is compared to that of the steady state at different cycle periods. It is found that the history of the operation mode has influence on the attained conversion, pointing to the existence of hysteresis affecting the particle wetting. <![CDATA[Formulation and numeric calculation of non-isothermal effectiveness factor for finite cylindrical catalysts with bi-dimensional diffusion]]> A model for calculating the effectiveness factor and the concentration and temperature profiles for finite cylindrical either hollow or solid catalyst particles is presented. The model accounts for dispersion in both radial and axial directions and non-isothermal behavior. The resulting differential partial equations system is discretized by a centered finite difference method and a program written for the Excel&trade; electronic sheet solves the highly nonlinear algebraic system. The numerical technique can be extended for any kinetic expression; for illustration, some results for n-th order reactions rate expressions are shown. <![CDATA[X-ray fluorescence analytical methodology for the determination of Nb, Ta, Fe and Mn extracted in hydrometallurgic processes]]> Analytical methodologies were developed for the quantification of niobium, tantalum, iron and manganese in samples of minerals and solid residues coming from ore pressure leaching, using different acids. The adopted instrumental technique was X-ray fluorescence on pelleted solid samples. The analysis of the experimental data obtained by the different assayed methods showed that the direct technique using calibration curves built from pure oxide patterns and the method of standard addition were those giving statistically acceptable results. Comparison of the analytical data obtained by application to ore and leaching residue samples of these methods with a reference method showed that the experimental results were satisfactory. <![CDATA[Dryout phenomenon in the periodic operation of a trickle bed reactor]]> Periodic operation was investigated for the hydrogenation of alpha-methylstyrene to cumene over 0.5% Pd on alumina spheres. The effect of several variables such as gas flow rate, gas and liquid composition, and liquid feed temperature on unsteady-state liquid flow modulation in a Trickle Bed Reactor is studied. These parameters affect the depletion time of the volatile reactant as well as the temperature profiles of the dry cycle. A criterion is presented that allows for an estimation of the maximum temperature during the dry cycle based on mass and energy balances. <![CDATA[Mixing characteristics of liquid phase in an unbaffled vessel agitated by unsteadily forward-reverse rotating multiple impellers]]> Mixing characteristics of liquid phase in an unbaffled vessel containing water with a liquid height-to-diameter ratio of 2 agitated by unsteadily forward-reverse rotating multiple impellers, a cross type of impellers with four delta blades (CDs), were experimentally studied in comparison with that in a baffled vessel agitated by steadily unidirectionally rotating disk turbine impellers with six flat blades (DTs). For the forward-reverse as well as unidirectional modes of operation, the mixing time in multiple impeller system was larger than that in single impeller system with a liquid height-to-diameter ratio of 1. The ratio of mixing time in multiple impeller system to that in single impeller system was small for the forward-reverse agitation mode compared with that for the unidirectional agitation mode. The result was discussed in relation to the difference in bulk flow pattern between the unbaffled vessel with forward-reverse rotating CDs and the baffled vessel with unidirectionally rotating DTs. <![CDATA[A generalized correlation for the second virial coefficient based upon the Stockmayer potential]]> We have approximated the second virial coefficients obtained from the Stockmayer potential using a two parameter, analytical correlation. The correlation eliminates the need for integration of the potential over nearly the entire range of reduced temperatures. The equation is valid from 0 to 1.5 reduced dipole moment and uses the Boyle temperature as a normalizing variable. Because the equation is a correlation, the parameters do not necessarily have any physical meaning. We have applied the new equation to nonpolar compounds, aromatics, freons, alcohols, ethers, aldehydes, and acids. <![CDATA[Sar despeckling filters in ultrasound imaging]]> Ultrasonics is a widely used technique in medical imaging, due to its noninvasive nature and its capability of forming real-time portraits of hidden targets. In this technique, pulse-echo ultrasonic waves are sent to the investigated medium and the backscattered waves provide the information for image formation. However, the coherent nature of the waves results in the appearance of speckle noise. This phenomenon is common to laser, sonar and synthetic aperture radar (SAR) imagery, and is the result of interference between the scattered waves. Many filters have been proposed for alleviating this noise, especially in remote sensing applications. Some of these filters (Mean, Median, Lee, Frost and Gaussian MAP) are reviewed and applied to ultrasound B-scan images, along with a non-linear technique based on computing the median on the binary slices of the data. The performance of these techniques is assessed both quantitatively (regarding noise suppression and radiometric preservation) and qualitatively (through perceptual contrast and edge preservation). <![CDATA[Air concentrations of SO<SUB>2</SUB> and wind turbulence near La Plata petrochemical pole (Argentina)]]> The aim of the present work is to show the correlation of the SO2 atmospheric concentration, taken in the surroundings of La Plata city, and the characteristics of the wind turbulence in such area. The first results indicate that there are a reasonable agreement between them. <![CDATA[A thermal tracing technique]]> A new thermal trace method is developed and tested in a water loop. Different measurements have been carried out to map the tracer concentration at a selected cross section downstream from the trace input location. Also bulk temperature increase was measured showing good agreement with the values calculated by energy balance. The method proposed gave meaningful information about the flow, opening the possibility of its application to the measurement of mixing rates between connected subchannels. <![CDATA[Exact travelling wave solutions to the generalized Kuramoto-Sivashinsky equation]]> By using a special transformation, the new exact travelling wave solutions to the generalized Kuramoto- Sivashinsky equation are obtained.