José P. Lopes Neto

Propriedades de fluxo de produtos pulverulentos alimentícios

Trying to provide more information about the flow of industrial solid materials, this research determined the flow properties of four powdered products manufactured by food industries and examined their levels of flowability, depending on the time of consolidation. The tests were conducted in the Jenike shear cell machine and consolidation bench. For determination of the flow index (FFC) and minimum diameter of the discharge orifice (D) Jenikes methodology was used and for minimum angle of the hopper, the Enstads method was adopted. It may be concluded that the consolidation time studied did not affect the flow properties of powdered materials and the minimum inclination of hopper angle was 60o. It was possible to determine the discharge orifice by Jenikes method only in case of wheat flour with a minimum value of 1.1 m for 24-hour period of consolidation.

Características de fluxo e projeto de tremonhas cônicas em silos verticais

For design involving storage of bulk solids to be safe and reliable, it is important to know a large number of variables such as flow properties, geometry of silos and flow pattern. With the objective to validate prediction using flow theories and silo design procedures, the flow properties of three bulk solids were determined and Jenikes flow theory and Enstads hopper design equations were applied and compared with those obtained experimentally in a reduced model of silo of semicircular section. The experimental results confirm the method of Jenike and Enstad for flow pattern and hopper design, respectively. The values of discharge orifice obtained by Jenikes equation are demonstrated to be oversized, being 45% higher than needed to provide flow.

Horizontal pressures in cylindrical metal silos and comparison with different international standards

Objetivou-se com este trabalho avaliar as pressoes horizontais em um silo metalico cilindrico de paredes corrugadas e fundo plano com 1,82 m de diâmetro e 5,4 m de altura, e comparar os valores com os obtidos teoricamente pelas normas ISO 11697, EP 433 e AS 3774. O silo foi carregado de forma simetrica e velocidade constante com trigo cv. soft red para duas diferentes relacoes de altura/diâmetro (H/D) e descarregado atraves de tres orificios com diâmetro de 71,6 mm, sendo um concentrico e dois excentricos. As pressoes horizontais foram medidas nas paredes do silo, em tres posicoes, utilizando-se de celulas de pressao tipo hidraulica. Os resultados mostraram que logo apos o inicio da descarga ocorreu fluxo de massa acima da cota de H/D = 1,2, enquanto abaixo desta cota se observou fluxo de funil. Pode-se afirmar que a norma EP 433 se mostrou mais adequada para predizer as pressoes horizontais em silos com relacao H/D = 1,0 com descargas excentricas. Para a relacao H/D = 1,5, a norma AS 3774 foi a que produziu valores mais proximos aos experimentais.

Powder flow criteria for design of vertical silo walls

For design of vertical silos walls involving the storage of bulk solids to be safe and reliable, it is important knowing the largest possible number of variables such as: flow properties, silo geometry and pattern of flow desired. In order to validate the theories of flow prediction and design of conical hoppers, the flow properties of two bulk solids were determined, the theories of Jenikes flowability and Enstad and Walker for hopper design were analyzed and the results were compared with those experimentally obtained in a reduced model of a semicircular-section silo. Results show that Enstad theory for the hopper design is adequate to occur mass flow inside the silo, and for the sizing of the discharge outlet, the Walkers theory was closer to the appropriate than Jenikes theory, which was higher around 100% than the experimental hopper outlet.

Análise estrutural de silos metálicos prismáticos

Nos ultimos anos, o crescimento da agricultura brasileira tem forcado varios setores a se adequarem aos padroes produtivos com o intuito de se manterem competitivos, frente ao processo de globalizacao economica. Nesse contexto, as fabricas de racao avicola tendem a buscar novas alternativas que favorecam a producao e reduzam custos sem afetar a qualidade do produto final. Entre essas alternativas, destaca-se o uso de silos verticais por facilitar o processo de confeccao das racoes e eliminar os grandes depositos horizontais. Diante dessa possibilidade, objetivou-se, com a presente pesquisa, estudar as tensoes nas paredes em conformacao ziguezague de um silo metalico prismatico 2m x 1m e comparar os resultados obtidos com teorias e normas. Para o calculo das tensoes, utilizaram-se os metodos simplificados de Ravenet e Troitsky. Para a obtencao dos esforcos reais nas paredes, utilizaram-se extensometros eletricos. Dessa forma, conclui-se que, tanto a teoria de Ravenet quanto de Troistky, podem ser recomendadas para o dimensionamento de silos prismaticos por apresentarem boa aproximacao com valores experimentais.

Propriedade de fluxo e característica de escoabilidade de rações avícolas para dimensionamento de silos

The knowledge about the physical and flow properties of industrial powders is very important to their handling and processing. With the right application of this information, its possible to design conveyors and storage systems to predict the ideal kind of flow for each operation. This work had the objective to determinate the physical and flow properties of different kinds of poultry rations and to evaluate their influences on geometric characteristics of hoppers. For that, it was used the direct shear apparatus based on Jenike shear cell and two friction surfaces: smooth and rough steel walls. To determinate the index flow (ffc) and minimum hopper opening diameter (D), was used the Jenikes methodology. For the minimum conical hopper angle, was used the mathematical method advised by British Standard BMHB. With the basis on obtained results, its possible to affirm that A and B poultry rations were classified as cohesive flow while the B poultry ration had the minors conical hopper angle and the higher hopper opening diameter.

Propriedades mecânicas e de fluxo de produtos agroindustriais

In the calculation of structures of silos comes up, over time, the use of new tools and methods aiming to determine the characteristics of storable products. The objective of this study was to determine the mechanical and flow properties of granular products such as grains of rice and ground corn at moisture contents of 10, 12 and 14% and cassava flour properties, which is considered as a powder with levels of humidity of 10 to 12%. For the determination of mechanical properties, compression tests were performed on cell specially made for this purpose. Four compression loads (5, 10, 15 and 20 kN) were used. The flow properties tests were conducted using translational shear equipment combined with Jenike Shear Cell. All assays were performed during the period from July to September, 2012. It may be stated that the results meet the criteria of the methodology flow pattern and those adopted by international standards; the average values of the mechanical properties were consistent to the ones found in the literature.

Forças verticais e de atrito em silos cilíndricos com fundo plano

The exact prediction of the forces that act on the vertical walls of silo is major problem when it comes to the question of design of these structures. In order to measure the forces acting on the bottom and vertical walls of the silo, the vertical wall and the bottom of a pilot vertical flat-bottom cylindrical silo was instrumented through load cells and pressure cells. The cell readings were performed by automatic data acquisition during loading and unloading of dry sand. The silo was concentrically loaded and concentric and eccentrically unloaded from two eccentricities. The experiment took place during the period from January to April 2008 at the Environment and Rural Construction Laboratory of Federal University of Campina Grande, Paraiba. The experimental values were compared with the standards Eurocode 1, ISO 11697, AS 3774 and DIN 1055. It can be concluded that theoretical values of vertical force were overestimated when compared with experimental results for majority of unloading methods. For friction forces on silo walls, the values from standards were compatible with the experimental results.

Forças de atrito em silos verticais de paredes lisas em diferentes relações altura/diâmetro

For the development of silo designs, it is necessary that factors such as flow and loads be carefully evaluated. Therefore, the main objective of this work is to measure, analyze and evaluate international standards of friction forces on the walls of a cylindrical silo with flat bottom. For the measurement of friction forces, two sets of three load cells and a data acquisition system were used. The silo was concentrically loaded with dry sand, and concentrically and eccentrically discharged from two eccentricities through holes of 80 mm diameter. The results show that the pilot silo model is suitable for measuring the friction forces on the walls, and that the theoretical values proposed by AS 3774 and DIN 1055 standards are more appropriate for the representation of friction forces in both concentric and eccentric discharging for all studied height/diameter ratios.

Concrete blocks for the modular construction of circular silos

At present it is estimated that 25% of the production of grains produced in Brazil is lost during harvest and post harvest phases but this can be reduced, in case, the country stimulates the storage of production. With the intention of promoting the storage of production in an economically viavel form, this work had the objective of studying the use of concrete blocks in the construction of circular silos. A block was developed with special geometry, moulded with mortar of 1:3, 1:4 and 1:6 (cement: sand), which was analyzed by water absorption, compression and shear strength tests and submitted to two types of cure: natural and submerged. Among the studied mixtures which achieved the compression resistance required by ABNT 7173 were 1:3 and 1:4. Since there is no specific norm for tension strength, a methodology was developed to simulate the tension force to which the walls of the circular silos are submitted; the blocks molded with 1:3 and 1:4 mortars achieved strength necessary for a silo with height of 4.0 m and height/diameter ratio equal to 1.