Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.

Sea Salt Aerosol Production: Mechanisms, Methods, Measurements, and Models - A Critical Review

This article mainly addresses the issues associated with the engineering of large-scale free suspension culture in agitated bioreactors >10,000 L because they have become the system of choice industrially. It is particularly concerned with problems that become increasingly important as the scale increases. However, very few papers have been written that are actually based on such large-scale studies and the few that do rarely address any of the issues quantitatively. Hence, it is necessary very often to extrapolate from small-scale work and this review tries to pull the two types of study together. It is shown that 'shear sensitivity' due to agitation and bursting bubbles is no longer considered a major problem. Homogeneity becomes increasingly important with respect to pH and nutrients at the largest scale and sub-surface feeding is recommended despite 'cleaning in place' concerns. There are still major questions with cell retention/recycle systems at these scales, either because of fouling, of capacity or of potential and different 'shear sensitivity' questions. Fed-batch operation gives rise to cell densities that have led to the use of oxygen and enriched air to meet oxygen demands. This strategy, in turn, gives rise to a CO(2) evolution rate that impacts on pH control, pCO(2) and osmolality. These interactions are difficult to resolve but if higher sparge and agitation intensities could be used to achieve the necessary oxygen transfer, the problem would largely disappear. Thus, the perception of 'shear sensitivity' is still impacting on the development of animal cell culture at the commercial scale. Microcarrier culture is also briefly addressed. Finally, some recommendations for bioreactor configuration and operating strategy are given.

Reactor engineering in large scale animal cell culture.

Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...

Multiphase catalytic reactors: a perspective on current knowledge and future trends

When a small air bubble bursts from an equilibrium position at an air/water interface, a complex motion ensues resulting in the production of a high-speed liquid jet. This free-surface motion following the burst is modelled numerically using a boundary integral method. Jet formation and liquid entrainment rates from jet breakup into drops are calculated and compared with existing experimental evidence. In order to investigate viscous effects, a boundary layer is included in the calculations by employing a time-stepping technique which allows the boundary mesh to remain orthogonal to the surface. This allows an approximation of the vorticity development in the region of boundary-layer separation during jet formation. Calculated values of pressure and energy dissipation rates in the fluid indicate a violent motion, particularly for smaller bubbles. This has important implications for the biological industry where animal cells in bioreactors have been found to be killed by the presence of small bubbles.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112093002216

Gas bubbles bursting at a free surface

Animal-cell damage in sparged bioreactors

In this paper, the second in the series, the use of a microscopic, high-speed video system to study the interactions of two suspended insect cells strains, Trichoplusia ni (TN-368) and Spodoptera frugiperda (SF-9), with rupturing bubbles is reported. Events such as the adsorption of cells onto the bubble film and the mechanism of bubble rupture were observed. On the basis of these observations and the experimental and theoretical work of other researchers on bubble rupture and cell death as a result of sparging, it is proposed that cells are killed by the rapid acceleration of the bubble film after rupture and the high levels of shear stress in the boundary layer flow associated with bubble jet formation.

Microscopic Visualization of Insect Cell-Bubble Interactions. II: The Bubble Film and Bubble Rupture

Through the use of microscopic, high-speed video technology, the interactions of two suspended insect cell lines, Trichoplusia ni (TN-368) and Spodoptera frugiperda (SF-9), with air and oxygen bubbles were studied. Events such as cell-bubble attachment, cell-bubble collision, cell transport into the foam layer, and trapping of cells in the foam layer are presented and discussed. Based on these observations and those in a companion paper (Chalmers, J. J.; Bavarian, F. Biotechnol. Prog. 1991, following paper in this issue) and the experimental and theoretical work of other researchers, several mechanisms of cell damage as a result of sparging are presented.

Microscopic visualization of insect cell-bubble interactions. I: Rising bubbles, air-medium interface, and the foam layer

Experiments were performed to study the hydrodynamic characteristics of a cocurrent, gas-liquid-solid fluidized bed containing cylindrical hydrotreating catalysts under conditions of high gas holdup. These conditions were established using an aqueous t-pentanol (0.5 wt. %) solution as the liquid phase in an attempt to simulate reaction conditions for hydrotreating of residual oils and coal liquefaction. Separate three-phase experiments were performed with air and water to investigate the effect of surface tension on hydrodynamic behavior.

A mathematical model was developed to describe the minimum fluidization velocity behavior. Bed voidage, gas holdup and terminal velocity of the particles were analyzed and correlated empirically to investigate the effect of particle shape and liquid surface tension. A bubble-wakes interaction coefficient defined by Jean and Fan (1987) was determined for cylindrical particles.

Hydrodynamics of three‐phase fluidized bed containing cylindrical hydrotreating catalysts

Hydrodynamics of gas—liquid—solid fluidization under high gas hold-up conditions

Experiments are performed under batch-liquid operating conditions to investigate the effect of static liquid height on the gas-liquid mass transfer coefficient (KLa) in a draft-tube bubble column (DTBC) and a draft-tube three-phase fluidized bed (DTFB). In addition, the effects of column diameter, gas-distributor, and draft-tube diameter are studied. The results indicate that for a given system with a porous plate gas-distributor at low superficial gas velocities (<70 m/hr), increasing static liquid height decreases KLa. At high gas velocities, KLa is independent of the static liquid height. For systems with a perforated gas-distributor, there is no effect of static liquid height on KLa. The formation of small dispersed bubbles at low gas velocities in the porous plate distributor system accounts for the considerably high KLa values and the observed effect of liquid height. On the other hand, the formation of large spherical-cap bubbles and the bubble coalescence at high gas velocities reduce the performa...

Farshad Bavarian

Papers

Microscopic Visualization of Insect Cell-Bubble Interactions. II: The Bubble Film and Bubble Rupture

Microscopic visualization of insect cell-bubble interactions. I: Rising bubbles, air-medium interface, and the foam layer

Hydrodynamics of three‐phase fluidized bed containing cylindrical hydrotreating catalysts

Hydrodynamics of gas—liquid—solid fluidization under high gas hold-up conditions

Effect of static liquid height on gas-liquid mass transfer in a draft-tube bubble column and three-phase fluidized bed