Rafael C. Silva

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.

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.

Erratum to: The effects of two preservatives on peroxidase activity and total protein content in Strelitzia reginae during cold storage

This study aimed to assess changes in peroxidase activity and total protein content of cut flowers of Strelitzia reginae that were treated with the chemical preservatives 8-hydroxyquinoline citrate (8-HQC) or chlorine during cold storage. The bases of the cut flowers were immersed in 1.5 L of tap water with 48 h pulsing treatments (a control with no chemical preservatives (0 mg·L-1, 100 mg·L-1 chlorine, 250 mg·L-1 8-HQC or 500 mg·L-1 8-HQC) during cold storage at 10.5°C and 90% relative humidity. The solutions were then replaced with tap water and the cut flowers remained in cold storage for 12 days. For biochemical characterization of peroxidase activity and total protein content, tissue samples (sepals, petals, stems, and bracts) were collected and analyzed at 0, 4, 8, and 12 days after treatment. There was an increase in peroxidase activity in petals, stems, and bracts and a decrease in total protein content, regardless of the treatment used. In this experiment, therefore, differences in peroxidase activity and total protein content due to treatments with 8-HQC or chlorine were not identified.

Effect of Time Storage of Poultry Ration for Design of Silos

Among the factors that affect the flow of solid products, the storage time stands out being responsible for promoting the appearance of cohesive arches. Thus, the present research had as objective to determine the properties of two poultry feed types, to classify them through the flowability depending on the consolidation time and to analyze their effects in metallic hoppers. For achieving this purpose, a direct shear apparatus known as “Jenike shear cell”, a consolidation bench and two wall surfaces were used. For the index flow and minimum diameter of the discharge hole, it was used the Jenike’s methodology. For conical hopper angle the Enstad’s methodology was adopted. It can be affirmed that the two feed types presented easy flow, not depending on the storage period. The roughness walls affected only the hopper slope, while results of discharge hole weren’t affected by variation of the properties of feed types on walls surfaces and the studied elapsed times.