Automated Compartment Model Development Based on Data from Flow-Following Sensor Devices

Due to the heterogeneous nature of large-scale fermentation processes they cannot be modelled as ideally mixed reactors, and therefore flow models are necessary to accurately represent the processes. Computational fluid dynamics (CFD) is used more and more to derive flow fields for the modelling of bioprocesses, but the computational demands associated with simulation of multiphase systems with biokinetics still limits their wide applicability. Hence, a demand for simpler flow models persists. In this study, an approach to develop data-based flow models in the form of compartment models is presented, which utilizes axial-flow rates obtained from flow-following sensor devices in combination with a proposed procedure for automatic zoning of volume. The approach requires little experimental effort and eliminates the necessity for computational determination of inter-compartmental flow rates and manual zoning. The concept has been demonstrated in a 580 L stirred vessel, of which models have been developed for two types of impellers with varying agitation intensities. The sensor device measurements were corroborated by CFD simulations, and the performance of the developed compartment models was evaluated by comparing predicted mixing times with experimentally determined mixing times. The data-based compartment models predicted the mixing times for all examined conditions with relative errors in the range of 3–27%. The deviations were ascribed to limitations in the flow-following behavior of the sensor devices, whose sizes were relatively large compared to the examined system. The approach provides a versatile and automated flow modelling platform which can be applied to large-scale bioreactors.

CFD research on the influence of geometry characteristic on flow pattern and the transition mechanism in Rushton turbine stirred vessels

In this paper, the transient MRF approach coupled with the standard k-ε and SST k-ω turbulence models was employed to study the effect of bottom shape, impeller diameter (D J) and bottom height (H 2) on critical impeller off-bottom clearance (C). It was found the bottom shape and bottom height (H 2) have obvious influence on the flow pattern transition from double-loop to single-loop of RT impeller. The flow pattern transition mechanism was inferred to relate to the relationship between the space required by the lower circulation zone and the actual space. The boundary conditions of critical C were further concluded to help distinguish the flow pattern and receive the expected one in the stirred vessel design.

RESEARCH OF EXTERNAL MASS TRANSFER PROCESSES FOR ADSORPTION FROM SOLUTIONS IN A APPARATUS WITH STIRRING

A study has been mode of transport-controlled mass transfer-controlled to particles suspended in a stirred vessel. The motion of particle in a fluid was examined and a method of predicting relative velocities in terms of Kolmogoroff’s theory of local isotropic turbulence for mass transfer was outlined. To provide a more concrete visualization of complex wave form of turbulence, the concepts of eddies, of eddy velocity, scale (or wave number) and energy spectrum, have proved convenient. Large scale motions of scale contain almost all of the energy and they are directly responsible for energy diffusion throughout the stirring vessel by kinetic and pressure energies. However, almost no energy is dissipated by the large-scale energy-containing eddies. A scale of motion less than is responsible for convective energy transfer to even smaller eddy sires. At still smaller eddy scales, close to a characteristic microscale, both viscous energy dissipation and convection are the rule. The last range of eddies has been termed the universal equilibrium range. It has been further divided into a low eddy size region, the viscous dissipation subrange, and a larger eddy size region, the inertial convection subrange. Measurements of energy spectrum in mixing vessel are shown that there is a range, where the so called -(5/3) power law is effective. Accordingly, the theory of local isotropy of Kolmogoroff can be applied because existence of the internal subrange. As the integrated value of local energy dissipation rate agrees with the power per unit mass of liquid from the impeller, almost all energy from the impeller is viscous dissipated in eddies of microscale. The correlation for mass transfer to particles suspended in a stirred vessel is recommended. The results of experimental study are approximately 12 % above the predicted values.

CFD simulation of CO2 absorption by water-based TiO2 nanoparticles in a high pressure stirred vessel

This work presents the modeling and simulation of CO2 capture by a water-based Titanium dioxide (TiO2) solid nanoparticle in a stirred high-pressure vessel at a constant temperature. Photocatalytic material such as TiO2 has excellent properties, namely it is nontoxic, inexpensive, and non-polluting. CFD model equations are developed and solved using COMSOL software package. The effect of the concentration of a solid nanoparticle in a water-based TiO2 solution, the size of TiO2 nanoparticles and the rate of mixing on the CO2 absorption rate is investigated. A 2D mathematical model considers both shuttle and micro-convention mechanisms. Results reveal that the best TiO2 concentration range is between 0.5 and 1 kg/m3 and that a particle size of 10 nm is more efficient than higher particle sizes. A moderate mixing rate maximizes the CO2 removal rate. The theoretical predictions are validated using lab experimental data and those in the available literature. Results confirm that the model calculations match with the experimental results. Accordingly, the model successfully predicts the experimental data and can be used for further studies.

HYDRODYNAMIC ANALYSES OF THE FLOW PATTERNS IN STIRRED VESSEL OF TWO-BLADED IMPELLER

In this paper, the governing equations of continuity and momentum subjected to suitable boundary conditions have been solved numerically to investigate the fluid flow in stirred vessel of two-bladed impeller. The numerical simulations have been carried out in three-dimensions for laminar flow. The studied fluid was considered Newtonian and incompressible. Our research studied the effects of geometrical configurations of the two-bladed impeller and its rotational speed on fluid patterns and mechanical power consumption. The innovative point in this paper is that the blades of the impeller contain three equal-sized holes of circular cross-section. The diameter of the hole (d) to the impeller diameter (D) gives the ratio d/D. the impeller speed is controlled by the Reynolds number (Re). The obtained results have been illustrated and discussed for the range of following governing parameters: d/D = 0 to 0.4 and Re = 1 to 300. The results showed that the studied parameters have significant effects on fluid flow and consumption power and the perforated blades of ratio d/D = 0.133 is more efficient than plan blades. Also, a new correlation is proposed to describe the consumption power as function of d/D and Re.