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Bulk Solids: Properties and Characterization
Published in Enrique Ortega-Rivas, Unit Operations of Particulate Solids, 2016
The angle of repose is defined as the angle of the free surface of a pile of powder to the horizontal plane. Depending on the conditions under which the pile has been poured and how the angle is measured, different values of the angle can be obtained for the same powder. Several types of angle of repose are used to assess powder flowability in an empirical manner; the most commonly employed are the poured and the drained angles of repose. The former is measured on a pile poured freely onto a flat surface while the latter is measured on the conical surface of powder in a flat-bottomed container when the powder has been allowed to flow out through an orifice in the base. A standard method for measuring the poured angle of repose has been reported for alumina (British Standards Institution, 1970). As shown in Figure 2.20, a funnel is cut short and adapted into a bridge. The lower opening of the funnel is located 52 mm from a metal plate on which concentric circles have been engraved. The center of the smallest circle is aligned with the center of the funnel. The powder, which is noncohesive, is discharged through the funnel until the poured pile just touches the lower opening of the funnel. The concentric circles help in measuring easily the diameter of the poured pile and, since the height is fixed, by simple trigonometry the angle of repose is determined. Although, as mentioned, the method was developed for alumina, there is no reason why it may be applied for any other noncohesive, easily flowing, or free-flowing particulate system.
Transport and Storage of Food Products
Published in Dennis R. Heldman, Daryl B. Lund, Cristina M. Sabliov, Handbook of Food Engineering, 2018
The coefficient of friction between granular materials is equal to the tangent of the angle of internal friction of the material. The angle of repose is the angle made by a material with respect to the horizontal when piled. While it is generally assumed that the angle of friction and the angle of repose are approximately equal, for some materials, such as sorghum, the magnitudes of the two angles can be different (Mohsenin, 1986). There are two angles of repose, a static angle of repose taken up by a granular solid that is about to slide upon itself, and a dynamic angle of repose that arises in all cases where the bulk of the material is in motion, such as during discharging of solids from bins and hoppers.
Effects of Particle Shape on Angle of Repose
Published in Y. Kishino, Powders and Grains 2001, 2020
One of the ways to characterize a bulk of particles is to measure the static angle of repose. Six different angles have been identified by Brown and Richards (Brown & Richards 1970). Since the static angle of repose is independent of gravity, it can be considered as material property in the sense that if the particles are identical, it shows a unique value. The static angle of repose can be altered by mixing different size of particles and particles of different surface characteristics and shape. It is the effect of particle shape that this paper tries to give some insight by providing simulation results.
Powder characteristics of Al0.5CoCrFeMnNi high-entropy alloys fabricated by gas atomisation method
Published in Powder Metallurgy, 2021
Yeeun Lee, Cheenepalli Nagarjuna, Jun-Woo Song, Kwang Yong Jeong, Gian Song, Jinkyu Lee, Jong-Hyeon Lee, Soon-Jik Hong
Angle of repose: The angle of repose (AOR) can be measured when the powder falls freely through a funnel onto a horizontal plate by gravity and powder piled as cone shape, the formation of angle between slope of a powder pile and horizontal plane is called the angle of repose [21]. It is the most important powder characterisation technique to realise the powder flowability. In general, the smaller AOR indicates that the better flowability of powders. Table 1 shows the measurement of angle of repose for the as-atomised powders, it showed the lowest angle of repose about 23.57°, due to its spherical shape and fewer satellites on powder surface, indicating the powders have excellent flowability and reliable for AM applications. This methodology was recommended by ASTM for characterising the metal powder for AM applications [22]. In addition, Schulze et al. demonstrated the time taken to discharge powders through funnel can be considered as a measurement factor for evaluating the flowability [23]. Carr et al. [24] and Raymus et al. [25] demonstrated that angle of repose with below 30° shows exceptional flowability.
Freeze-drying of maple syrup: Efficient protocol formulation and evaluation of powder physicochemical properties
Published in Drying Technology, 2020
Sagar Bhatta, Tatjana Stevanovic, Cristina Ratti
Angle of repose (θ) determines the flow properties of a powder, and is defined as the angle formed by the free surface of a pile of powder with the horizontal plane. θ was measured by following the described method with slight modification.[13] Briefly, the glass funnel of 6 cm in diameter with a stem of 3.5 cm long (1 cm of stem diameter at the opening) was attached to a stand. The distance between the end of the funnel stem and flat surface was maintained at 4 cm. About 3 g of sample was poured in the funnel and the diameter of the base of the powder cone (measured at three different positions and averaged) and height of cone were recorded using a digital caliper (STM, S B Simpson Group Inc., ON, CA). Then, θ was calculated by using Eq. (5). where h is the height of conical pile, and r is the radius of horizontal base of powder.
Nutraceutical tablets from maqui berry (Aristotelia chilensis) spray-dried powders with high antioxidant levels
Published in Drying Technology, 2020
Francisco Garrido Makinistian, Loreana Gallo, Paula Sette, Daniela Salvatori, Verónica Bucalá
The angle of repose was determined by pouring around 2 g of spray-dried powder through a funnel located at a fixed height above a paper placed on a flat horizontal surface and measuring the height (h) and radius (r) of the conical pile formed. A height of 3 cm between the funnel bottom and the paper was selected to minimize the impact of falling powder on the tip of the cone. The angle of repose was calculated as the inverse tangent of the h/r ratio. Repose angles between 25° and 30° indicate excellent flowability, among 31°–35° the flow is good and within 36°–40° the flow is fair. Values higher than 41° represent poor flow properties.[21]