Numerical evaluation of the low Reynolds turbulent flow behaviour in a bioreactor

Koerich, Daniela M.; Rosa, Leonardo Machado da

doi:10.1504/ijspm.2016.075081

Cited by 11 publications

(6 citation statements)

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“…This flow rate corresponds to a nominal Reynolds number of 1689 . Little influence of the transition regime, below 3 %, was verified in this low Reynolds number flow . A turbulence intensity of 5 % was considered in the inlet duct, which corresponds to an average turbulence .…”

Section: Methodsmentioning

confidence: 98%

“…In Equation , the turbulent tensor

τ

resulting from the process of averaging the instantaneous equations was calculated using the Reynolds stress model (RSM). This is a more complete model, and requires little more computational time when compared with simpler approaches . The exact form of the transport equations for each Reynolds tensor component (

ρ_{l} \overset{u^{'} u^{'}}{true}

) can be written as follows:

\begin{matrix} right & center & left \frac{\partial}{\partial t} (α_{l} ρ_{l} \overline{u^{'} u^{'}}) + \nabla \cdot (α_{l} ρ_{l} U_{l} \overline{u^{'} u^{'}}) \\ right & center & left = - α_{l} ρ_{l} (\overline{u^{'} u^{'}} {(\nabla U_{l})}^{T} + (\nabla U_{l}) \overline{u^{'} u^{'}}) \\ right & center & left + \nabla α_{l} \cdot ([], μ_{l} \nabla \overset{u^{'} u^{'}}{true} + \frac{μ_{t}}{σ_{k}} \nabla \overset{u^{'} u^{'}}{true}) + α_{l} Φ - \frac{2}{3} α_{l} ρ_{l} ε I \end{matrix}

where I is the identity tensor, and

Φ

is the correlation pressure‐stress for an incompressible flow, which arises from the linear pressure‐strain model:

φ = φ_{1} + φ_{2} + φ_{w}

where

φ_{1}

is the slow pressure‐strain term,

φ_{2}

is the rapid pressure‐strain term, and

φ_{w}

is the wall‐reflection term.…”

Section: Methodsmentioning

confidence: 99%

“…This is a more complete model, and requires little more computational time when compared with simpler approaches. [18] The exact form of the transport equations for each Reynolds tensor component ( l u u ) can be written as follows:…”

Section: Flow and Mathematical Model Specificationmentioning

confidence: 99%

“…[12] Little influence of the transition regime, below 3 %, was verified in this low Reynolds number flow. [18] A turbulence intensity of 5 % was considered in the inlet duct, which corresponds to an average turbulence. [20] The other conditions, all with upward flow, consider flow rates even lower, equal to 189.4, 94.7, 47.3, and 23.6 g/s.…”

Section: Boundary and Initial Conditionsmentioning

confidence: 99%

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Optimization of bioreactor operating conditions using computational fluid dynamics techniques

Koerich

Rosa

2016

Can J Chem Eng

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High hydraulic retention times are commonly used in bioreactors, as they provide greater contact time between substrate and biomass. These reactors also operate at low flow rates to minimize damage to the biomass due to shear stress and drag. However, a high flow rate provides greater mixing, and thus the optimal operation condition is difficult to estimate. In this study, the effect of different flow rates on the behaviour of the phases in an anaerobic sequencing batch bioreactor is evaluated numerically. Fluent 15 code was used, considering the two‐phase, transient, and turbulent flow in a three‐dimensional mesh. The turbulence, the drag of the biomass flocs to the recirculation system, and the shear stress in the remaining solids were evaluated. For the reactor evaluated in this study, the flow rate of 189.4 g/s was found to be the most suitable, not only for the operation of the reactor, but also to provide energy savings in the operation of the recirculation pump.

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Section: Methodsmentioning

confidence: 98%

“…In Equation , the turbulent tensor

τ

ρ_{l} \overset{u^{'} u^{'}}{true}

) can be written as follows:

\begin{matrix} right & center & left \frac{\partial}{\partial t} (α_{l} ρ_{l} \overline{u^{'} u^{'}}) + \nabla \cdot (α_{l} ρ_{l} U_{l} \overline{u^{'} u^{'}}) \\ right & center & left = - α_{l} ρ_{l} (\overline{u^{'} u^{'}} {(\nabla U_{l})}^{T} + (\nabla U_{l}) \overline{u^{'} u^{'}}) \\ right & center & left + \nabla α_{l} \cdot ([], μ_{l} \nabla \overset{u^{'} u^{'}}{true} + \frac{μ_{t}}{σ_{k}} \nabla \overset{u^{'} u^{'}}{true}) + α_{l} Φ - \frac{2}{3} α_{l} ρ_{l} ε I \end{matrix}

where I is the identity tensor, and

Φ

is the correlation pressure‐stress for an incompressible flow, which arises from the linear pressure‐strain model:

φ = φ_{1} + φ_{2} + φ_{w}

where

φ_{1}

is the slow pressure‐strain term,

φ_{2}

is the rapid pressure‐strain term, and

φ_{w}

is the wall‐reflection term.…”

Section: Methodsmentioning

confidence: 99%

Section: Flow and Mathematical Model Specificationmentioning

confidence: 99%

Section: Boundary and Initial Conditionsmentioning

confidence: 99%

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Optimization of bioreactor operating conditions using computational fluid dynamics techniques

Koerich

Rosa

2016

Can J Chem Eng

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“…Finite volume method was used with Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm [13]. The solution is based on Reynolds Averaged Navier-Stokes equation with k-epsilon turbulence closure [14]. Calibration of the turbulence model parameter is based on empirically data reported in the literature [15].…”

Section: Methodsmentioning

confidence: 99%

Analysis of a mechanical mixer performance in anoxic reactor

Papp

Karches

2019

Pollack Periodica

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Denitrification is a key process in wastewater treatment since it is responsible for the effective nutrient removal. It requires anoxic conditions, where only chemically bound nitrogen is used as an oxygen source, and no aeration is applied. In suspended biomass systems the growth and homogenization of biomass is essential, high degree of mixing is required, which is achieved only by using mechanical mixers. Mechanical mixing performance relies on the mixing power determined by the equipment dimensions and rotational speed. In this paper the effect of three different rotational speed (rpm: 100, 400, 900 min-1) on flow field and mixing conditions are evaluated. As a result of the simulations, the acceptable flow field was achieved at 400 rpm. The outcome of this research is that the high degree of energy transfer from mixers to fluid flow deteriorated mixing efficiency.

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A Review on the Rheological Behavior of Organic Waste for CFD Modeling of Flows in Anaerobic Reactors

Caillet¹,

Adelard²

2022

Waste Biomass Valor

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Anaerobic digestion is a widely used process for organic waste treatment and renewable energy production. This is a complex natural biodegradation of organic matter involving four main biochemical reactions through the action of four microbial groups. The performances of anaerobic digestion (biodegradation and biogas production) depend on the contact between the biodegradable materials and the micro-organisms. Consequently, hydrodynamics phenomena have a significant impact on the anaerobic digestion. Computational Fluid Dynamics (CFD) simulations allow to simulate the flow field within anaerobic digesters. In these models, the waste are characterized by their physical properties, specifically their rheological properties. Rheology consists in the study of the flow of liquids or viscous materials. In this respect, it involves the properties related to the flow behavior of liquids and the temporary and/or permanent deformation of materials. The knowledge on the rheological properties of the biowaste is crucial in order to describe the flows using CFD models. The aim of this review is to present the physical properties of different type of waste, as well as the rheological models. In conclusion, the rheological behaviors of wastewater, manure, and sludge are described in literature. However the rheological behaviors of a mix of biowaste and solid food waste are poorly known. Research should focus on the experimental measurements of these biowaste. These data are necessary for CFD modeling of flows in anaerobic reactors treating this type of waste.

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Numerical evaluation of the low Reynolds turbulent flow behaviour in a bioreactor

Cited by 11 publications

References 0 publications

Optimization of bioreactor operating conditions using computational fluid dynamics techniques

Optimization of bioreactor operating conditions using computational fluid dynamics techniques

Analysis of a mechanical mixer performance in anoxic reactor

A Review on the Rheological Behavior of Organic Waste for CFD Modeling of Flows in Anaerobic Reactors

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