Hydrodynamics and mass transfer in miniaturized bubble column bioreactors

Miniaturized bubble columns (MBCs) have different hydrodynamics in comparison with the larger ones, but there is a lack of scientific data on MBCs. Hence, in this study, the effect of gas hold-up, flow regimes, bubble size distribution on volumetric oxygen mass transfer coefficient at different pore size spargers and gas flow rates in MBCs in the presence and absence of microorganisms were investigated. It was found that flow regime transition occurred around low gas flow rates of 1.18 and 0.85 cm/s for small (16–40 µm) and large (40–100 µm) pore size spargers, respectively. Gas hold-up and K_La in MBC with small size sparger were higher than those with larger one, with an increasing effect in the presence of microorganisms. A comparison revealed that the wall effect on the flow regime and gas hold-up in MBCs was greater than bench-scale bubble columns. The K_La values significantly increased up to tenfold using small pore size sparger. In the MBC and stirred tank bioreactors, the maximum obtained cell concentrations were OD₆₀₀ of 41.5 and 43.0, respectively. Furthermore, it was shown that in MBCs, higher K_La and lower turbulency could be achieved at the end of bubbly flow regime.

     

A nanoparticle in plasma

Charge and energy fluxes onto a nanoparticle under conditions typical of laboratory plasmas are investigated theoretically. Here, by a nanoparticle is meant a grain the size of which is much smaller than both the electron Larmor radius and Debye length and the thermionic emission from which is not limited by the space charge. Under conditions at which thermionic emission plays an important role, the electric potential and temperature T _p of a nanoparticle are determined by solving a self-consistent set of equations describing the balance of energy and charge fluxes onto the nanoparticle. It is shown that, when the degree of plasma ionization exceeds a critical level, the potential of the nanoparticle and the energy flux onto it increase with increasing nanoparticle temperature, so that, starting from a certain temperature, the nanoparticle potential becomes positive. The critical degree of ionization starting from which the potential of a nanoparticle is always positive is determined as a function of the plasma density and electron temperature. The nanoparticle temperature T _p corresponding to the equilibrium state of a positively charged nanoparticle is found as a function of the electron density for different electron temperatures.     

A Novel Transformation to S-Methyl Phosphorodichloridothiolate and the Fungitoxicity of Diaryl S-Methyl Phosphorothiolates

Prior to an analysis of the shrinkage and growth of air bubbles entrained in wheat flour dough, the shrinkage and growth under a temperature rise of a small bubble in water was analysed for comparison. The rates of shrinkage and growth of the bubble were respectively controlled by the diffusion of under- and over-saturated dissolved air from and into the bubble. The diffusion coefficient of the dissolved air in water calculated from the shrinkage of the bubble was 2.10 × 10^_9m²/sec (17°C), which agrees with the literature value. On the other hand, at below 100°C, the effects on the bubble growth of the expansion of air due to the temperature rise and the increase in the saturation vapor pressure of water were negligibly small. The accompanying air entrained in flour particles suspended in water was much more stable than a free bubble in water. However, the growth under a temperature-rise of a bubble evolved from wheat flour particles was the same as the growth of a bubble in water, if many bubbles did not coexist.     

Effect of additives on mass transfer in turbine aeration

Mass transfer coefficients and interfacial areas were determined for the aeration of aqueous solutions in a turbine agitated vessel. The mass transfer coefficients measured for water without additive and for sodium chloride solutions matched very well to measurements in the literature for air bubbles of the same diameter in free rise. Thus the only effect of agitation was to determine the bubble size which then in turn set the coefficient. Two surface active agents were studied: sodium dodecyl sulfate and Dow Corning Antifoam C. The rate of mass transfer increased with the former additive but decreased with the latter; however, the mass transfer coefficient was the exact same function of bubble diameter in both cases and the different rates are attributed to the quite different effects on interfacial area.     

Effect of surface contaminants on oxygen transfer in bubble column reactors

Gas hold-up (ɛ_g), sauter mean bubble diameter (d₃₂) and oxygen transfer coefficient (k_La) were evaluated at four different alkane concentrations (0.05, 0.1, 0.3 and 0.5 vol.%) in water over the range of superficial gas velocity (u_g) of (1.18–23.52) × 10⁻³ m/s at 25 °C in a laboratory-scale bubble column bioreactor. Immiscible hydrocarbons (n-decane, n-tridecane and n-hexadecane) were utilized in the experiments as impurity. A type of anionic surfactant was also employed in order to investigate the effect of addition of surfactant to organic-aqueous systems on sauter mean bubble diameter, gas hold-up and oxygen transfer coefficient. Influence of addition of alkanes on oxygen transfer coefficient and gas hold-up, was shown to be dependent on the superficial gas velocity. At superficial gas velocity below 0.5 × 10⁻³ m/s, addition of alkane in air–water medium has low influence on oxygen transfer coefficient and also gas hold-up, whereas; at higher gas velocities slight addition of alkane increases oxygen transfer coefficient and also gas hold-up. Increase in concentration of alkane resulted in increase in oxygen transfer coefficient and gas hold-up and roughly decrease in sauter mean bubble diameter, which was attributed to an increase in the coalescence-inhibiting tendency in the presence of surface contaminant molecules. Bubbles tend to become smaller with decreasing surface tension of hydrocarbon, thus, oxygen transfer coefficient increases due to increasing of specific gas–liquid interfacial area (a). Empirical correlations were proposed for evaluating gas hold-up as a function of sauter mean bubble diameter, superficial gas velocity and interfacial surface tension as well as evaluating Sherwood number as a function of Schmidt, Reynolds and Bond numbers.     

Influence of pluronic F68 on oxygen mass transfer

Pluronic F68 is one of the most used shear protecting additives in cell culture cultivations. It is well known from literature that such surface‐active surfactants lower the surface tension at the gas‐liquid interface, which influences the mass transfer. In this study, the effect of Pluronic F68 on oxygen mass transfer in aqueous solutions was examined. Therefore, the gassing in/gassing out method and bubble size measurements were used. At low concentrations of 0.02 g/L, a 50% reduction on mass transfer was observed for all tested spargers and working conditions. An explanation of the observed effects by means of Higbie's penetration or Dankwerts surface renewal theory was applied. It could be demonstrated that the suppressed movement of the bubble surface layer is the main cause for the significant drop down of the k_La‐values. For Pluronic F68 concentrations above 0.1 g/L, it was observed that it comes to changes in bubble appearance and bubble size strongly dependent on the sparger type. By using the bubble size measurement data, it could be shown that only small changes in mass transfer coefficient (k_L) take place above the critical micelle concentration. Further changes on overall mass transfer at higher Pluronic F68 concentrations are mainly based on increasing of gas holdup and, more importantly, by increasing of the surface area available for mass transfer. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1278–1288, 2013     

Dry Matter and Water Import Rates in the Tomato Fruit: a Model Incorporating the Changes in Sap Viscosity and Osmotic Potential with Temperature

The change in water import rate in tomato fruit was modelledby incorporating into a previously-published model the changesin sap viscosity and osmotic potential into fruit with temperature.An experimental relationship between water and dry matter importrates was used to compare the model to dry matter import ratesin fruit measured by Walker and Thornley (Annals of Botany 41:977-985, 1997) at different temperatures. The effect of temperatureon the water import rate, calculated from the model, was alsocompared with the effect of temperature on the fruit growthrate measured by Pearce, Grange and Hardwick (Journal of HorticulturalScience 68: 1-11 and 13-23, 1993). The model accounted for alarge part of these temperature effects. It was concluded that resistances in sap transfer pathways inthe tomato fruit could be due to viscosity. These results supported,on the one hand, the hypothesis that the progressive decreaseof water import rate during fruit growth could result partlyfrom the progressive increase in transfer pathway length, and,on the other hand, the hypothesis that the ratio between waterand dry matter import rates could depend on flow conditionsin transfer pathways. The equations of the model could be usedto simulate tomato fruit growth, mass and dry matter contentin relation to fruit size, to nutrient solution salinity andto fruit temperature.Copyright 1995, 1999 Academic Press Dry matter, fruit, growth, model, resistance, sap, temperature, tomato, transfer, viscosity, water     

The influence of polymeric membrane gas spargers on hydrodynamics and mass transfer in bubble column bioreactors

Gas sparging performances of a flat sheet and tubular polymeric membranes were investigated in 3.1 m bubble column bioreactor operated in a semi batch mode. Air–water and air–CMC (Carboxymethyl cellulose) solutions of 0.5, 0.75 and 1.0 % w/w were used as interacting gas–liquid mediums. CMC solutions were employed in the study to simulate rheological properties of bioreactor broth. Gas holdup, bubble size distribution, interfacial area and gas–liquid mass transfer were studied in the homogeneous bubbly flow hydrodynamic regime with superficial gas velocity (U _G) range of 0.0004–0.0025 m/s. The study indicated that the tubular membrane sparger produced the highest gas holdup and densely populated fine bubbles with narrow size distribution. An increase in liquid viscosity promoted a shift in bubble size distribution to large stable bubbles and smaller specific interfacial area. The tubular membrane sparger achieved greater interfacial area and an enhanced overall mass transfer coefficient (K _La) by a factor of 1.2–1.9 compared to the flat sheet membrane.     

Effect of dielectric constant of medium on protonation equilibria of ethylenediamine

Abstract

The effect of dielectric constant of medium on protonation equilibria has been studied by determining protonation constants of ethylenediamine pH metrically in various concentrations (0–60%v/v) of acetoni-trile– and ethylene glycol–water mixtures, at an ionic strength of 0.16mol L^?1 and at 303.0 K. MINIQUAD75 computer program has been used for the calculation of protonation constants. Linear and non-linear variations of step-wise protonation constants with reciprocal of dielectric constant of the solvent mixtures have been attributed to the dominance of the electrostatic and non-electrostatic forces, respectively. The trend is explained on the basis of solute–solute and solute–solvent interactions, solvation, proton transfer processes and dielectric constants of the media.     

Effects of Extraction Parameters on Particle Size of Titanium Dioxide Nanopowders Prepared by Physical Vapor Deposition Technique

In this work, the effects of different extraction parameters on the particle size of the nanopowders extracted from titanium dioxide thin film samples were studied. These nanopowders were obtained by the conjunctional freezing-assisted ultrasonic extraction method. Titanium dioxide thin films were different in their structures (anatase-only, rutile-only, and mixed phase), and their structural characteristics were determined. Results showed that extraction parameters such as freezing temperature, ultrasonic frequency, and application time are very effective in determining the nanoparticle size, which is very important for many applications and uses of highly pure nanomaterials and nanostructures.

     

Investigation of the structure of two-phase flow model-media in bubble-column bioreactors

Summary By applying photographic, electrical conductivity, and electrooptical methods, the transverse variation of bubble size and velocity, the local gas holdup, and the local specific gas/liquid interfacial area were estimated in a bench scale bubble-column bioreactor containing distilled water. The liquid velocity profile, the transverse turbulence intensity variations, and the turbulence energy dissipation scale were also measured by a hot film turbulence probe and constant temperature anemometer technique.     

Response of <Emphasis Type="Italic">Tisochrysis lutea</Emphasis> [Prymnesiophycidae] to aeration conditions in a bench-scale photobioreactor

The effects of superficial gas velocity (U_gr), gas entrance velocity (ν), and bubble size on the growth of Tisochrysis lutea was investigated in 600-mL photobioreactors operated with airlift pumps. Superficial gas velocities, calculated from measured air flow rates, ranging from 7 to 93 mm s^?1 were created using a 1.6-mm diameter syringe. We tested the effects of sparger velocity over a range of 2.48 to 73.4 m s^?1 and the effects of bubble size by using two styles of air stones and an open glass pipette, which created a bubble sizes in the range of 0.5 to 5 mm. We calculated oxygen mass transfer coefficient, k_La, values for all experimental conditions. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicated that smaller bubble size leads to some initial cell damage, but after time, the increased gas transfer as reflected by the k_La value produced higher growth than larger bubbles. Two mechanisms were observed to correlate with cell damage in T. lutea: increasing velocity at the sparger tip and bubble bursting at the surface. These results demonstrate a method to test sensitivity of T. lutea to aeration, which is important for the design of airlift systems.     

The Mass Culture of Porphyridium cruentum

A study was made of the effect of temperature, detention period, light intensity, and salinity on the growth rate and over-all light energy conversion efficiency of Porphyridium cruentum cultured on a medium consisting of concentrated sea water and sewage enriched with urea, chelated iron, and other additives. It was found that the optimal temperature was within the range of 21 to 26 C. Growth was retarded at temperatures less than 13 C, and completely inhibited above 31 C. Over-all light energy conversion efficiency increased from 2.24% at the 4-day detention period to 2.76% at the 10-day period. Conversion efficiency ranged from 5.8% at a light energy absorption rate of 8.2 cal:liter:min to 2.3% at 35 to 39 cal:liter:min.

At salt concentrations less than 3.5%, Porphyridium could not successfully compete with other algae in open cultures. Salt concentrations as high as 4.6% had no inhibitory effect on its growth.

In studies on nutrition, it was found that growth on a medium of salts used in formulating synthetic sea water dissolved in sewage was equal to that on a control medium consisting of concentrated sea water and sewage (see above). They showed that sewage contains a substance or substances essential for optimal growth. Vitamin B₁₂ alone could not substitute for it.

     

The Effect of Thermophoresis on Unsteady Oldroyd-B Nanofluid Flow over Stretching Surface

There are currently only a few theoretical studies on convective heat transfer in polymer nanocomposites. In this paper, the unsteady incompressible flow of a polymer nanocomposite represented by an Oldroyd-B nanofluid along a stretching sheet is investigated. Recent studies have assumed that the nanoparticle fraction can be actively controlled on the boundary, similar to the temperature. However, in practice, such control presents significant challenges and in this study the nanoparticle flux at the boundary surface is assumed to be zero. We have used a relatively novel numerical scheme; the spectral relaxation method to solve the momentum, heat and mass transport equations. The accuracy of the solutions has been determined by benchmarking the results against the quasilinearisation method. We have conducted a parametric study to determine the influence of the fluid parameters on the heat and mass transfer coefficients.     

Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

     

Bubble coalescence in air-sparged bioreactors

Coalescence frequency has been measured in an air-sparged bubble column by observing the rate with which insoluble tracer gases were mixed within the dispersed gas phase. The effects of gas-sparge rate and salt concentration were examined. Coalescence frequencies increased with increasing gas-sparge rates approximately in proportion to the increase in gas-phase hold up. The coalescence frequency decreased with NaCI concentration to a minimum frequency about half the frequency observed in pure water. Bubble size distributions were also measured in the air-sparged column. The size distribution changed significantly over the same range of NaCI concentration as variations in the coalescence frequency were observed. The gas-sparge rate showed no effect on the bubble size.     

Double-diffusion convective biomimetic flow of nanofluid in a complex divergent porous wavy medium under magnetic effects

We explore the physical influence of magnetic field on double-diffusive convection in complex biomimetic (peristaltic) propulsion of nanofluid through a two-dimensional divergent channel. Additionally, porosity effects along with rheological properties of the fluid are also retained in the analysis. The mathematical model is developed by equations of continuity, momentum, energy, and mass concentration. First, scaling analysis is introduced to simplify the rheological equations in the wave frame of reference and then get the final form of equations after applying the low Reynolds number and lubrication approach. The obtained equations are solved analytically by using integration method. Physical interpretation of velocity, pressure gradient, pumping phenomena, trapping phenomena, heat, and mass transfer mechanisms are discussed in detail under magnetic and porous environment. The magnitude of velocity profile is reduced by increasing Grashof parameter. The bolus circulations disappeared from trapping phenomena for larger strength of magnetic and porosity medium. The magnitude of temperature profile and mass concentration are increasing by enhancing the Brownian motion parameter. This study can be productive in manufacturing non-uniform and divergent shapes of micro-lab-chip devices for thermal engineering, industrial, and medical technologies.

     

Glass microspargers as effective frit spargers in single use bioreactors

For multiple-use bench scale and larger bioreactors, sintered stainless steel frit spargers are commonly used as microspargers. For bench-scale single-use bioreactors (SUBs), existing microspargers are sintered plastics, such as polyethylene. However, though plastics are readily sterilized by irradiation making them convenient for single use, these designs overlook surface energy properties of the materials of construction. For these sintered plastic spargers, forces at the water-air-surface interface cause bubble coalescence, leading to lower effective mass transfer, higher gas flow rates, and differing pCO₂ profiles in cell culture. Alternative materials of construction were evaluated based on contact angle information and bubble formation observations. Sintered glass was chosen over thermoplastic polymers for higher surface wettability as described in the glass/water contact angle, its history as a commonly sintered material, and availability at costs suitable for single use applications. Glass sintered spargers and traditional stainless steel frit spargers were compared by porosity, bubble size, and k_La studies. Mass transfer (k_La) and cell culture performance equal or greater than a standard 20 μm stainless steel microsparger mass transfer efficiency was achieved by a glass frit sparger, of international porosity standard “P40” according to ISO 4793-80, which corresponds to a range of 16–40 μm.     

Effect of Water Diffusion Limitations on the Thermostability of Enzymes in Non-Aqueous Environments

The thermostability of anhydrous α-chymotrypsin has been analysed both in air and in organic solvents, with regard to the effect of the protein water-content on the course of deactivation. A higher initial water content increases the rate of inactivation.

Deactivation tests carried out under a constant thermodynamic activity of water indicate that reductions in dehydration rate lead to lower stability.

The effect of water diffusion phenomena has also been studied. Protein aggregates of larger size are less thermostable, thus indicating that diffusional limitations to water transfer can play a significant role in thermoinactivation.

The effect of water content on enzyme thermostability was also measured in the presence of two organic solvents of different hydrophobicity. In both cases, the resulting increased thermolability can be explained in terms of a limitation in water transfer towards the non-aqueous environment.     

Photosynthesis, Transpiration, Leaf Temperature, and Stomatal Activity of Cotton Plants under Varying Water Potentials

Cotton plants, Gossypium hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperature, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.

Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.

Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4° above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.

Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.

Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplitude and frequency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.

Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only on leaves that were previously under high light intensity.