On the design and simulation of an airlift loop bioreactor with microbubble generation by fluidic oscillation

Microbubble generation by a novel fluidic oscillator driven approach is analyzed, with a view to identifying the key design elements and their differences from standard approaches to airlift loop bioreactor design. The microbubble generation mechanism has been shown to achieve high mass transfer rates by the decrease of the bubble diameter, by hydrodynamic stabilization that avoids coalescence increasing the bubble diameter, and by longer residence times offsetting slower convection. The fluidic oscillator approach also decreases the friction losses in pipe networks and in nozzles/diffusers due to boundary layer disruption, so there is actually an energetic consumption savings in using this approach over steady flow. These dual advantages make the microbubble generation approach a promising component of a novel airlift loop bioreactor whose design is presented here. The equipment, control system for flow and temperature, and the optimization of the nozzle bank for the gas distribution system are presented. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V All rights reserved

Photobioreactor Design and Fluid Dynamics

Photobioreactor design is a subject of great relevance for the attainment of a sustained development in modern technology,and has also considerable interest from the basic scientific and technologic point of view.The aim of the present review paper is presenting and comparing some of the recent attempts by the authors of modelling photosynthesis in reactors.A short inspection of the kinetic models proposed for photobioreactor design is done,and some examples of the integration of such kinetic models and bioreactor fluid dynamics in the modelling of photobioreactors are presented

Modeling tobacco mosaic virus proliferation in protoplasts

The tobacco mosaic virus (TMV) is one of the most studied viruses. It is frequently used as a model in the research of virus-host interactions. The interest in understanding the mechanism of its proliferation stems basically from the field of agriculture, due to the detrimental effect this virus has on several crops. In addition to this direct application, virus-mediated protein expression systems, which are well established for the synthesis of foreign proteins in animal cell cultures, are now being applied to plants and plant cells by means of plant viral vectors. The use of transformed roots for the propagation of viral vectors has also been proposed. This work presents a mechanistic model describing the transient process of TMV multiplication in a protoplast (a wall-deprived cell). It aims to be a mathematical tool able to simulate the transient behavior of the main molecular pools taking part in the process, which will be useful for exploring, understanding and predicting the dynamics of a host-virus system. The variables considered are the pools of the main molecules taking part in the viral replication process. The basic balance equations for the cellular pools are presented and a satisfactory fit of the model to the experimental data is shown. The presented model is a necessary step toward the formulation of a basic mechanistic model for the systemic propagation of the virus in a plant tissue. It may be extended in many directions as to the optimization of a system for the production of a foreign protein, to the simulation of manipulation of the virus-cell interaction by external factors, to the mechanism of gene silencing or to the prediction of co-infection dynamics.Fil: Merchuk, Jose C. Ben-Gurion University of the Negev; IsraelFil: Sánchez-Mirón, Asterio. Universidad de Almería; EspañaFil: Asurmendi, Sebastian. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Biotecnología; ArgentinaFil: Shacham, Mordechai. Ben-Gurion University of the Negev; Israe

Experiments on gas transfer to a film of blood through a membrane

The result of an increase in mean saturation of blood predicted by two mathematical models was verified by means of a series of experiments using cattle blood flowing in a 1.1 mm thick film, with flow rates ranging between 0.6 and 2.5 cc/min. The use of the equation of O2 transfer without taking into account the coupled CO2 transfer leads to slightly conservative predictions, and experimental data fit the calculated values of saturation within an error of 5%. For very slow flow rates the deviations reach 10%.Facultad de Ingenierí

Gas absorption with second-order chemical reaction in a packed column : Effects of contact-time distribution

Absorption of carbon dioxide into aqueous solution of sodium hydroxide was studied in a packed column under conditions such that the accompanying reaction was of the second order. In this case the average or volumetric reaction factor for the packed column, i.e. the ratio of the volumetric coefficients for absorption with and without chemical reaction, is complicated by the non-uniform contact-time distribution. However, the assumption of Porter''s "long, slow flow paths" model for the contact-time distribution led to a successful correlation for the average reaction factor.Facultad de Ingenierí

Gas-liquid mass transfer : a comparison of down-and up-pumping axial flow impellers with radial impellers

The performance of a down- and up-pumping pitched blade turbine and A315 for gas-liquid dispersion and mass transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory scale vessel. The results show that when the axial flow impellers are operated in the up-pumping mode, the overall performance is largely improved compared with the down-pumping configuration. Compared with the radial turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine and is economically much more efficient in terms of mass transfer than both turbines. On the other hand, the uppumping pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of the pitched blade turbine

Void Fraction Measurement of Gas-Liquid Two-Phase Flow from Differential Pressure

Void fraction is an important process variable for the volume and mass computation required for transportation of gas–liquid mixture in pipelines, storage in tanks, metering and custody transfer. Inaccurate measurement would introduce errors in product measurement with potentials for loss of revenue. Accurate measurement is often constrained by invasive and expensive online measurement techniques. This work focuses on the use of cost effective and non-invasive pressure sensors to calculate the gas void fraction of gas–liquid flow. The differential pressure readings from the vertical upward bubbly and slug air–water flow are substituted into classical mathematical models based on energy conservation to derive the void fraction. Electrical Resistance Tomography (ERT) and Wire-mesh Sensor (WMS) are used as benchmark to validate the void fraction obtained from the differential pressure. Consequently the model is able to produce reasonable agreement with ERT and WMS on the void fraction measurement. The effect of the friction loss on the mathematical models is also investigated and discussed. It is concluded the friction loss cannot be neglected, particularly when gas void fraction is less than 0.2

Experimental pulse technique for the study of microbial kinetics in continuous culture

A novel technique was developed for studying the growth kinetics of microorganisms in continuous culture. The method is based on following small perturbations of a chemostat culture by on-line measurement of the dynamic response in oxygen consumption rates. A mathematical model, incorporating microbial kinetics and mass transfer between gas and liquid phases, was applied to interpret the data. Facilitating the use of very small disturbances, the technique is non-disruptive as well as fast and accurate. The technique was used to study the growth kinetics of two cultures, Methylosinus trichosporium OB3b growing on methane, both in the presence and in the absence of copper, and Burkholderia (Pseudomonas) cepacia G4 growing on phenol. Using headspace flushes, gas blocks and liquid substrate pulse experiments, estimates for limiting substrate concentrations, maximum conversion rates Vmax and half saturation constants Ks could rapidly be obtained. For M. trichosporium OB3b it was found that it had a far higher affinity for methane when particulate methane monooxygenase (pMMO) was expressed than when the soluble form (sMMO) was expressed under copper limitation. While for B. cepacia G4 the oxygen consumption pattern during a phenol pulse in the chemostat indicated that phenol was transiently converted to an intermediate (4-hydroxy-2-oxovalerate), so that initially less oxygen was used per mole of phenol.

Infection Units: A novel approach for modeling COVID-19 spread

A novel mechanistic model of COVID-19 spread is presented. The pool of infected individuals is not homogeneously mixed but is viewed as a passage into which individuals enter upon the contagion, through which they pass (in the manner of “plug flow”) and exit at their recovery points within a fixed time. Our novel concept of infection unit is defined. The model separately considers various population pools: two of symptomatic and asymptomatic infected patients; three different pools of recovered individuals; of assisted hospitalized patients; of the quarantined; and of those who die from COVID-19. Transmission of this disease is described by an infection rate function, modulated by an encounter frequency function. This definition makes redundant the addition of a separate pool for the exposed, as done in several other models. Simulations are presented. The effects of social restrictions and of quarantine policies on pandemic spread are demonstrated. The model differs conceptually from others of the kind in the description of the transmission dynamics of the disease. A set of experimental data is used to calibrate our model, which predicts the dynamic behavior of each of the defined pools during pandemic spread

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable.European Community - ‘Improving Human Research Potential’ - Marie Curie Fellowship - contract number HPMF-CT-2002-01643