José Renato Coury

Avaliação de estratégias para redução da deriva de agrotóxicos em pulverizações hidráulicas

Pesticide spray drift is a major problem in agriculture today. Among the factors influencing drift, droplet size is of paramount importance. Thus, this work aimed to evaluate the effects of adding emulsifying vegetable oil to the pesticide emulsion and using low drift nozzles on droplet spectrum formation and, consequently, on the drift potential of fan spray nozzles. Droplet distribution was measured under controlled atmosphere, using a real time laser particle size analyzer. The droplets were generated with standard nozzles, with and without the addition of adjuvants, and with low drift nozzles, with the operating pressure ranging from 200 to 400 kPa. Also, drift was evaluated in the field, using artificial targets placed outside the application area, where droplet counting was accomplished. The results showed that both the addition of vegetable oil to the pesticide emulsion and the use of low drift nozzles altered droplet size spectra, increasing the diameter of the drops and reducing the percentage of drops subject to wind action being, thus, effective factors in drift reduction.

Influence of gas velocity on cake formation and detachment

Abstract This work presents an experimental study of the influence of gas velocity during filtration on cake formation and its removal. The experimental data were obtained using a polyester felt of squared section, with an area of 0.0225 m 2 , through which the dust laden air was driven. The behaviour of the filter during filtration and cleaning was studied using four filtration velocities (0.048; 0.067; 0.074 and 0.089 m s −1 ). For each filtration velocity, four cakes with different thicknesses were tested. For each cake formed, the cleaning of the fabric was performed using the reverse flow technique, and the cake/fabric adhesion force was estimated. The results showed that the cake porosity decreased and the cake specific resistance increased with increase in the superficial velocity of filtration. Also, for the same powder (dust) being fed, the mean particle size of the material forming the cake increased with increasing filtration velocity, probably due to particle settling before reaching the filter. The cake/fabric adhesion force was estimated as well as the effective distance between the particle surfaces. The calculated values of both were well within the range reported in the literature. The former increased and the latter decreased with increase in the superficial velocity of filtration.

Espectro de gotas de bicos de pulverização hidráulicos de jato plano e de jato cônico vazio

A escolha e o uso adequado de bicos de pulverizacao sao essenciais para a correta aplicacao de agrotoxicos. Este trabalho teve como objetivo avaliar o espectro de gotas de bicos de pulverizacao hidraulicos de jato plano padrao e de jato conico vazio, com diferentes vazoes nominais. Em ambiente controlado, avaliou-se o espectro de gotas por meio de um analisador a laser de gotas em tempo real, nas faixas de pressao de 200 a 400 kPa para os bicos de jato plano, e de 400 a 600 kPa para os bicos de jato conico vazio. Realizou-se tambem um estudo teorico sobre a distância horizontal percorrida por gotas de tamanho conhecido. Os bicos de jato conico vazio apresentaram gotas de menor tamanho em relacao aos de jato plano e, por isso, proporcionaram maior densidade de gotas depositadas sobre a superficie-alvo. Todos os bicos apresentaram densidade de gotas superior a 110 gotas cm-2. No entanto, o potencial de deriva foi alto, principalmente o dos bicos de jato conico, requerendo estrategias para sua reducao. E possivel estimar a distância horizontal percorrida por gotas de tamanho conhecido.

Permeability optimization and performance evaluation of hot aerosol filters made using foam incorporated alumina suspension

Porous ceramic samples were prepared from aqueous foam incorporated alumina suspension for application as hot aerosol filtering membrane. The procedure for establishment of membrane features required to maintain a desired flow condition was theoretically described and experimental work was designed to prepare ceramic membranes to meet the predicted criteria. Two best membranes, thus prepared, were selected for permeability tests up to 700 degrees C and their total and fractional collection efficiencies were experimentally evaluated. Reasonably good performance was achieved at room temperature, while at 700 degrees C, increased permeability was obtained with significant reduction in collection efficiency, which was explained by a combination of thermal expansion of the structure and changes in the gas properties.

Drop size measurements in Venturi scrubbers

Venturi scrubbers are high efficiency gas cleaners in which suspended particles are removed from gas streams by drops formed by liquid atomisation, usually in the Venturi throat. The size of the drops formed are of fundamental importance to the performance of the equipment, both in terms of pressure drop and dust removal efficiency. In this study, drop sizes in a cylindrical laboratory-scale Venturi scrubber were measured using a laser diffraction technique. Gas velocity and liquid to gas ratios varied from 50 to 90m/s and 0.5 to 2.0l/m3, respectively. Water was injected using two different arrangements: either as jets in the throat or as a flim just upstream of the convergence. Drop size measurements were performed at three positions in the case of jet injection: two located along the throat, and the last one at the end of the diffuser. The present data shows that the Sauter mean diameter of the spray can be well correlated by the equation of Boll et al. (J. Air Pollut. Control Assoc. 24 (1974) 932). Drop size distributions are satisfactorily represented by a Rosin–Rammler function. This paper also provides a simple method for calculating the parameters of the Rosin–Rammler function. As a result of this work, drop sizes in Venturi scrubbers can be estimated with much higher accuracy.

Rupture of dry agglomerates

Abstract The application of two distinct physical concepts to the phenomena of rupture of dry agglomerates has been discussed. The classical theory proposed by Rumpf states that particle separation occurs when the adhesion forces are supplanted by the applied removal force, causing a simultaneous breakage of interparticle links along the rupture plane. Kendall and co-workers argue that this concept overestimates the energy necessary for breakage and propose that separation occurs from the nucleation of cracks in ‘defects’ previously present in the agglomerate structure, with the energy consumption being proportional to the formation of the new surfaces. Two different kinds of dry agglomerates of the same material, filtration cakes and tumbling drum granules, had their rupture stresses experimentally estimated in laboratory conditions. These values were then used for discussing the theories of Rumpf and Kendall. The results indicate that neither theoretical approach could represent the two practical situations: Rumpfs theory seems to be more adequate for the cake removal process whilst Kendalls theory explains better the granule crushing mechanism. The conditions at the time of agglomerate formation could explain these observations, as they are reasonably well connected to the fundamental assumptions of the respective theoretical approaches.

Evaluation of the models available for the prediction of pressure drop in venturi scrubbers.

The major running cost derived from the operation of venturi scrubbers is pressure drop. In the present study, the predictions of different models are compared to experimental data from venturi scrubbers of different sizes (throat diameter from 1.9 to 16cm), geometries, operating variables and liquid injection arrangements. As a result, it is concluded that most of the models must be used with caution. Much attention must be paid to the validity of the assumptions employed in the mathematical models. The equations proposed by Calvert [Scrubbing, Air Pollution, 3rd Edition, Vol. IV, Academic Press, New York, 1982], Yung et al. [JAPCA 27 (1977) 348] or Hesketh [Atomization and cloud behaviour in wet scrubbers, in: Proceedings of the US-USSR Symposium Control Fine Particulate Emissions 1974, San Francisco, 15-18 January 1974] produce good results only in very specific situations. The model proposed by Boll [Ind. Eng. Chem. Fundam. 12 (1973) 40] is simple, easy to compute and agrees reasonably well with the experimental data. Unfortunately, it cannot predict the effect of different liquid injection arrangements. The model by Azzopardi and coworkers [Filtr. Sep. 21 (1984) 196; Trans. IchemE. 69B (1991) 237; Chem Eng. J. 67 (1997) 9] was the only one to give good predictions for all the range of variables studied. On the other hand, this model is not simple and requires from the engineer an additional effort in terms of computation. In order to apply this model to the rectangular geometry, the concept of hydraulic equivalent diameter was used.

Capture and rebound of dust in granular bed gas filters

Abstract Experimental data for the efficiency of filtration of gases by fixed beds of granular solids are used to evaluate the reliability of the ‘cell’ and ‘constricted tube’ models for gas flow and aerosol transport. The dominant capture mechanisms are Brownian diffusion and inertial deposition. For Brownian diffusion, both models give sensible estimates for capture efficiency, but this process is shown to be insensitive to the model assumptions. Inertial deposition provides a much more sensitive test, and it is shown that neither model gives satisfactory predictions for the efficiency of inertial capture. Whether a dust particle adheres or rebounds on contacting a filter granule depends on the relative importance of kinetic and adhesion energies. An approach is proposed which enables the theoretical analyses to be applied to predict the limits of adhesion.

Droplet size in a rectangular Venturi scrubber

The Venturi scrubber is a device which uses liquid in the form of droplets to efficiently remove fine particulate matter from gaseous streams. Droplet size is of fundamental importance for the scrubber performance. In the present experimental study, a laser diffraction technique was used in order to measure droplet size in situ in a Venturi scrubber with a rectangular cross section. Droplet size distribution was measured as a function of gas velocity (58.3 to 74.9 m/s), liquid-to-gas ratio (0.07 to 0.27 l/m3), and distance from liquid injection point (64 to 173 mm). It was found that all these variables significantly affect droplet size. The results were compared with the predictions from correlations found in the literature.

Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber.

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.