A backmixing model describing micromixing in single-phase continuous-flow systems

Zwietering, Th.N.

doi:10.1016/0009-2509(84)80112-8

Cited by 30 publications

(13 citation statements)

References 11 publications

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“…The model illustrated in Figure 13 is similar in its physical representation of the flow to the plume engulfment model proposed by Zwietering 40. The plume engulfment model has been applied to general reactive mixing problems, and considers incoming fluid volumes to have varying “ages.” Fluid volumes that have just entered the reactor are “young,” and become closer to the bulk conditions as their age increases.…”

Section: Detailed Modeling Of Mixing and Reaction In The Ldpe Autoclavementioning

confidence: 99%

Mixing effects on performance and stability of low‐density polyethylene reactors

Wells

Ray

2005

AIChE Journal

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Section: Detailed Modeling Of Mixing and Reaction In The Ldpe Autoclavementioning

confidence: 99%

Mixing effects on performance and stability of low‐density polyethylene reactors

Wells

Ray

2005

AIChE Journal

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“…Autoclaves account for about half of the total LDPE production. Zwietering (1984) presented a "plume model" where the plume of the feed jet would exponentially grow by mixing with the bulk until concentrations inside the plume become the same as those in the bulk. Relatively high feed flow rates and short residence times that are typical for these reactors often result in a feed jet with composition and temperature significantly different from the rest of the reactor vessel.…”

Section: Introductionmentioning

confidence: 99%

A Study of Macrosegregation in Low-Density Polyethylene Autoclave Reactors by Computational Fluid Dynamic Modeling

Tosun

Bakker²

1997

Ind. Eng. Chem. Res.

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Flow and reaction in a typical commercial scale autoclave LDPE reactor were modeled by a three-dimensional computational fluid dynamic (CFD) k-model in order to shed light on the macrosegregation effects that can occur in these reactors. It is shown that the CFD model predicts significant differences from CSTR behavior. Results are discussed in terms of the effects of macro-and microscale inhomogeneities of concentration and temperature on free radical polymerization kinetics. The observed nonidealities in terms of minima in the initiator consumption curves and multiple steady states are explained on the basis of competing turbulent transport and chemical kinetics. Microsegregation effects are shown to be negligible in comparison to macrosegregation effects. Given the fact that the CFD model is based on reactive scalar and energy balances without adjusted parameters in the three-dimensional flow field of the entire reactor, it is tentatively concluded that commercial-scale LDPE vessel reactors can have significant macrosegregation effects beyond a certain steady-state adiabatic operating temperature that is specific to the initiator being used.

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“…A model describing the micromixing is crucial to understand and to control the continuous fluidized bed drying process. Zwietering et al distinguished two extreme cases through two models–the segregation model (SM) and the maximum mixedness model (MMM).…”

Section: Resultsmentioning

confidence: 99%

“…In the SM, the powders are broken up into discrete fragments characterized by particles with identical moisture contents. Figure depicts a schematic of the SM . The particle stream flows through a PFR with outlets following the arrows.…”

Section: Resultsmentioning

confidence: 99%

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Continuous fluidized bed drying: Residence time distribution characterization and effluent moisture content prediction

et al. 2020

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The mixing and drying behavior in a continuous fluidized bed dryer were investigated experimentally by characterizing the residence time distribution (RTD) and incorporating a micromixing model together with the drying kinetics obtained from batch drying. The RTD of the dryer was modeled using a tank‐in‐series model. It was found that a high initial material loading and a low material flow rate resulted in a reduced peak height and broaded peak width of the RTD curve. To predict the continuous dryer effluent moisture content, we combined: (a) the drying kinetics as determined in a batch fluidized bed dryer, (b) the RTD model, and (c) micromixing models—segregation and maximum mixedness models. It was found that the segregation model overpredicted the effluent moisture content by up to 5% for the cases we have studied while the maximum mixedness model gave a good prediction of the effluent moisture content.

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A backmixing model describing micromixing in single-phase continuous-flow systems

Cited by 30 publications

References 11 publications

Mixing effects on performance and stability of low‐density polyethylene reactors

Mixing effects on performance and stability of low‐density polyethylene reactors

A Study of Macrosegregation in Low-Density Polyethylene Autoclave Reactors by Computational Fluid Dynamic Modeling

Continuous fluidized bed drying: Residence time distribution characterization and effluent moisture content prediction

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