The effect of operating temperature on the velocity of minimum fluidization, bed voidage and general behaviour

Botterill, J.S.M.; Teoman, Y.; Yüregir, K.R.

doi:10.1016/0032-5910(82)80009-0

Cited by 93 publications

(48 citation statements)

References 14 publications

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“…In contrast, no systematic thermal effect was observed in the sub-4 mm samples. The tendency of high temperature to loosen packing and increase voidage has been reported from particles including silica sand, glass ballotini, salt and cracking catalyst (Botterill et al 1982;Lucas et al 1986;Raso et al 1992;Yamazaki et al 1995;Formisani et al 1998;Lettieri et al 2000Lettieri et al , 2002. It has been attributed either to growth of cohesive forces (Raso et al 1992;Yamazaki et al 1995;Formisani et al 1998) or to hydrodynamic effects related to the positive influence of temperature on gas viscosity (Lucas et al 1986).…”

Section: Resultsmentioning

confidence: 93%

Gas retention in fine-grained pyroclastic flow materials at high temperatures

et al. 2007

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International audienceThe ability of a dense pyroclastic flow to maintain high gas pore pressure, and hence low friction, during runout is determined by (1) the strengths and longevities of gas sources, and (2) the ability of the material to retain residual gas once those sources become ineffective. The latter is termed the gas retention capacity. Gas retention capacity in a defluidizing granular material is governed by three timescales: one for the evacuation of bubbles (t be ; brief and not considered in this paper), one for hindered settling from the expanded state (t sett), and one for diffusive release of residual pore pressure from the non-expanded state (t diff). The relative magnitides of t sett and t diff depend on bed thickness, t sett dominating in thin systems and t diff in thick ones. Three pyroclastic flow materials, two ignimbrites and a block-and-ash flow sample, were studied experimentally to investigate expansion behaviour under gas flow and to determine gas retention times. Effects of particle size were evaluated by using two size cuts (<4 mm and <250 μm) from each sample. Careful drying of the materials was necessary to avoid effects of humidity-related cohesion. Two sets of experiments were carried out: (1) expansion in the non-bubbling regime at 50–200°C, (2) bed collapse tests from the initially bubbling state at 50–550°C. Provided that gas channelling was avoided by gentle stirring, all the samples exhibited a regime of uniform expansion prior to the onset of bubbling. Fine particle size (in particular high fines content), low particle density and high temperature all favoured smoother fluidization by increasing the maximum expansion possible in the non-bubbling state. An empirical equation describing the uniform expansion of the materials was determined. High temperature also favoured greater gas partitioning into the dense phase of the bubbling bed, as well (in finer-grained samples) as higher voidage in the settled bed. Large values of t sett and t diff were favoured by fine particle size. Temperature had less influence, suggesting that experimental results at low temperatures (50–200°C) can be extrapolated to higher temperatures. Gas retention times provide insight into the ability of pyroclastic flows in expanded (t sett) or non-expanded (t diff) flow states to retain gas once air ingestion or gas production have become ineffective. Finer-grained pyroclastic flows are expected to retain gas longer, and hence to have higher apparent ‘mobilities', than coarser-grained ones of comparable volume, as has been observed on Montserrat

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Section: Resultsmentioning

confidence: 93%

Gas retention in fine-grained pyroclastic flow materials at high temperatures

et al. 2007

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“…Along with the wide applications of fluidized beds to the industry, the prediction errors of Umf at high temperature began to attract more attention. Botterill et al (1982) [29] have observed that the U of Geldart B-type particles decreases with the increasing bed temperature, opposite to the behaviour of Geldart D-type particles. Pattipati and Wen [30] have pointed out that the increasing temperature causes a slight decrease of Umf for particles, whose diameter is smaller than 2 mm, unlike particles larger than 2 mm.…”

Section: Literature Surveymentioning

confidence: 93%

Hydrodynamic Studies on Conventional and Tapered Fluidized Bed

2016

IJSR

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Abstract:In this project the determination of maximum pressure drop, minimum fluidization velocity, minimum bubbling velocity and fluidization index for various powders are to be studied using a conventional cylindrical bed and a tapered bed. Tapered beds have a velocity gradient along the axis unlike conventional beds. They have been used as an alternative to conventional cylindrical beds to deal with problems such as slugging. Initially air at ambient conditions (310 K) is to be used as the fluidizing medium. High temperature studies will also be carried out using a High temperature fluidized bed (Air temperature up to 1173 K).

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“…Minimum fluidization tests were carried out according to the standard method (Davidson and Harrison, 1971) applied by many investigators (Rowe and Yacono, 1976;Botterill et al, 1982).…”

Section: Measurements Of Minimum Fluidization Velocitiesmentioning

confidence: 99%

Investigation of the bubble behaviour at the free surface of a large three-dimensional gas fluidized bed

Hepbaşlı

1998

Int. J. Energy Res.

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The effect of operating temperature on the velocity of minimum fluidization, bed voidage and general behaviour

Cited by 93 publications

References 14 publications

Gas retention in fine-grained pyroclastic flow materials at high temperatures

Gas retention in fine-grained pyroclastic flow materials at high temperatures

Hydrodynamic Studies on Conventional and Tapered Fluidized Bed

Investigation of the bubble behaviour at the free surface of a large three-dimensional gas fluidized bed

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