An approximate theory for pressures and arching in hoppers

Vacuum assisted flow initiation in arching powders

“…Typically arching occurs when the exit diameter is smaller than a "critical orifice diameter", which can be measured using standard equipment [5]. Podczeck and Jones [6] use critical orifice diameter as a measure of the ability of a powder to form an arch while others [7] use it to describe flowability whereby a better flowing powder has a smaller critical orifice diameter.…”

“…Jenike's investigation [20,21] lead to development of a model to calculate the geometry of a mass flow hopper in order to avoid arch formation. Walker's theoretical studies [7] determined the approximate stresses within the powder flowing through a hopper. Drescher and co-workers [22,23] compared the experimental critical orifice sizes with the values obtained from theoretical analysis and demonstrated that the theories overestimate the critical orifice size as a result of neglecting selfweight of powder above the exit.…”

Normal pressures and frictional tractions on shallow conical hopper walls after concentric filling: Predictions and experiments

“…Except in very slender silos, the hopper supports the majority of the weight of stored solid (Rotter, 2001), so the loading on it is important for structural integrity assessments. However, the pressures on the hopper wall change from the condition after filling to that during discharge (Walker, 1966;Jenike et al, 1973;Walters, 1973;Enstad, 1975;Rotter, 1999Rotter, , 2001EN 1991EN -4, 2006) and this has a significant impact on the structural design of the hopper (Teng and Rotter, 1991).…”

“…To produce a useful solution, two assumptions are then made: a) the ratio of the average horizontal pressure against the wall to the average vertical stress over a horizontal section is constant throughout the silo height; the value of this constant depends on whether the material is freshly deposited or discharging (Rotter, 2008), sometimes imagined to be in a Rankine active state or passive state (Nedderman, 1992); and b) the wall friction is fully mobilised and remains constant throughout the whole silo height, a condition which may be met if the wall is uniform and the hopper is steep (Rotter, 2001;Ding et al, 2011). Different authors later derived the corresponding differential equation for a slice in a linearly tapering channel, which could be either conical or wedged-shaped (Dabrowski, 1957;Walker, 1966;Walters, 1973;McLean and Arnold, 1976;Enstad, 1981Enstad, , 1975. Most of these theories used the slice treatment of Janssen, but they then made different assumptions concerning the evaluation of the ratio of wall pressures to vertical pressures.…”

Pressões e fluxo em silos esbeltos (h/d≥1,5)

“…A primeira corresponde a uma inclinação muito utilizada em silos e corresponde a análise para silos com fluxo de funil. Já a segunda foi determinada pela equação (4) sugerida por McLEAN (1986), visando a obtenção de fluxo de massa para a pior situação (soja) como se pode inferir a seguir: WALKER (1966) e JENIKE (1968,1973,1977 e as normas ISO 11697 (1995), EUROCODE 1/Part 4 (1995), AS 3774 (1996) e DIN 1005-6 (2000. Para o cálculo das pressões no corpo do silo, tendo em vista que as paredes do silo analisadas são de chapa metálica corrugada, o ângulo de atrito com a parede foi considerado igual ao ângulo de atrito interno.…”