Transition Phenomenon Investigation Between Different Flow Regimes in a Rotary Drum

Santos, D.A.; Scatena, R.; Duarte, Cláudio Roberto; Barrozo, M. A. S.

doi:10.1590/0104-6632.20160333s20150128

Cited by 13 publications

(5 citation statements)

References 34 publications

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“…Figure shows that with an increase in the filling degree, the critical rotational speed ( ω c ) decreases for both green and roasted coffee beans. This behaviour was also found by previous studies, which show that with higher drum filling degrees, lower rotational speeds are required to centrifuge the material inside the drum. It can also be seen (Figure ) that the critical rotational speed ( ω c ) was higher for green coffee beans compared with the roasted ones.…”

Section: Resultssupporting

confidence: 86%

“…However, none of the correlations in literature were able to adequately predict the critical rotational speed ( ω c ), since the experimental data showed that for lower values of filling degrees, higher rotation speeds are required in order to centrifuge the material. It is worth noting that the aforementioned correlations have been determined for spheres, which may explain the poor performance of these correlations to predict the critical rotational speed for green and roasted coffee beans, whose particle geometry is not spherical …”

Section: Resultsmentioning

confidence: 99%

“…Although the rotary drum is a relatively simple device, particle dynamics inside these equipment is complex. Concerning the behaviour of granulated material in rotary drums, there are recent studies using different particles such as wheat, soybeans, rice, and corn, under different operating conditions for drum rotational speed and filling degree. Another relevant work carried out by GDR MiDi presents an attempt to quantify the relevant variables responsible for main mechanisms controlling the granular flow in different equipment's geometries.…”

Section: Introductionmentioning

confidence: 99%

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An experimental analysis of coffee beans dynamics in a rotary drum

et al. 2017

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Brazil is the largest producer and exporter of coffee in the world, one of the main global commodities. During the processing of coffee beans, rotary drums are used in the drying and roasting phases. This equipment is widely used in many industrial sectors. According to characteristics of the drum, particulate material, and operating conditions, different flow regimes may arise. Such regimes have a direct influence on the performance of these processes and therefore their characterization is of great importance. The present work developed an experimental study about the dynamics of coffee beans, under green and roasted conditions, in a rotary drum. Transitions between rolling, cascading, cataracting, and centrifuging regimes were evaluated, for both green and roasted coffee beans. For the centrifuging regime, a comparison between experimental critical rotation speeds and the ones obtained by correlations found in literature was performed. Additionally, a new expression to predict the centrifuging rotation speed was proposed by the authors. Further analyses regarding the rolling regime were also carried out. For this regime, velocity profiles of the particles were evaluated, as well as the thickness of the active layer for different filling degrees and drum rotation speeds. Great similarity was found between the behaviour of the active region for coffee beans before and after the roasting process.

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Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An experimental analysis of coffee beans dynamics in a rotary drum

et al. 2017

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“…Hysteresis transitions of the circulation and wall layer modes during the rapid rotation of the drum for non-cohesive [41] and cohesive [42] granular fillers were also found experimentally. However, these works ignore the possibility of self-excitation of self-oscillations of the filler during such motion mode transitions.…”

Section: Literature Review and Problem Statementmentioning

confidence: 55%

Revealing the mechanism of stability loss of a two-fraction granular flow in a rotating drum

Deineka

Naumenko

2022

EEJET

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The qualitative nature and quantitative parameters of motion instability of a two-fraction granular filler of a rotating drum were determined. The factors of motion instability and key parameters of the oscillating system were identified and their influence on the self-excitation of pulsed self-oscillations was estimated. Two continuous and one periodic steady-state modes of filler motion were found. Periodic self-oscillations due to the development of instability during the transition from continuous circulation mode to the wall layer mode were revealed. As factors of motion instability, filler dilatancy and damping effect of fine fraction particles on the pulsed interaction of coarse fraction particles were taken. It turned out that the main key parameter of the oscillating system is the drum speed, which determines a change in dilatancy. The increase in instability is realized as a reduction of the bifurcation values of speed and dilatancy. Other key parameters are the content of the fine fraction in the filler κff and the filling degree of the chamber κlf, the growth of which increases the self-oscillating instability. The features of the oscillatory system are the relaxation type, discontinuous nature of self-oscillations and hard self-excitation mode under bistability. The discontinuous character and oscillatory hysteresis increase with decreasing κff and κlf. The limit values of the dynamic motion parameters corresponding to the conditions of self-excitation of self-oscillations in the absence and presence of fine fraction were determined: 0.96–1.11 and 0.218–0.382 for the bifurcation value of relative speed, 0.745–0.855 and 0.24–0.322 for the bifurcation value of dilatancy. The effects found make it possible to substantiate the parameters of the self-oscillating process of processing polygranular materials in drum-type machines.

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“…The authors of [41] experimentally studied the speed limits of the existence of a near-wall layer of loose granular fill of the rotating drum chamber. The influence of physical properties, sphericity, and density of particle material, and internal and external friction was considered.…”

Section: Literature Review and Problem Statementmentioning

confidence: 99%

Establishing the conditions for the formation of a near-wall layer of solid granular fill of a rotating drum

Naumenko¹,

Deineka²,

Myronenko³

2021

EEJET

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This paper reports the assessment of the influence of dynamic motion parameters on the formation and disappearance at the cylindrical surface of the chamber of the rotating drum of the near-wall layer of non-loose granular fill. Based on the results of experimental visualization of the flow, the effect of solidity on the behavior of granular fill was revealed. The hydrodynamic effect of fill quasi-liquefaction under the action of solidity has been established, which involves the occurrence of a connecting interaction between adjacent layers and the surface of the chamber. Conversion of shear circulation flow to homogeneous dense clustered stream with slipping and rolling without relative movement of particles was detected. The hydrodynamic characteristics of circulation flow transition to the near-wall layer mode during rotation acceleration have been defined. Such a transition is implemented by smoothly increasing the thickness of the layer when the rest of the fill is circulated at the bottom of the chamber. The effect of the rheological hysteresis of the movement of the rotating chamber fill, caused by quasi-liquefaction of non-loose granular environment, has been established. The effect implies exceeding the speed limit ωfl in the formation of a near-wall layer, at rotation acceleration, above the boundary ωdl of the layer disappearance when the rotation slows down. The manifestation of hysteresis mainly increases with an increase in Reynolds number. The intensity of increased hysteresis manifestation increases with a decrease in the degree of filling the chamber. The value of the Froud number for the ωfl and ωdl boundaries increases with the increase in Re. It has been established that at the relative particle size of the dispersed fill ψdc≈(0.065–1.04)·10‑3 and Re=30–500, Fr=1–2.9, for the ωfl boundary, and Fr=0.5–1.4, for the ωdl boundary. The Fr value for the ωfl limit was found to exceed this value for the ωdl boundary by 1.6–2.1 times. The established effects make it possible to substantiate the rational parameters for the grinding process in drum-roll mills

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Transition Phenomenon Investigation Between Different Flow Regimes in a Rotary Drum

Cited by 13 publications

References 34 publications

An experimental analysis of coffee beans dynamics in a rotary drum

An experimental analysis of coffee beans dynamics in a rotary drum

Revealing the mechanism of stability loss of a two-fraction granular flow in a rotating drum

Establishing the conditions for the formation of a near-wall layer of solid granular fill of a rotating drum

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