Bubble-free liquid cell

Gas-liquid-biosolid Bubble-free membrane gassing gas diffuses into the media without bubbles. Used for shear-sensitive animal cell cultures (ex insect cells) and for systems containing serum that are prone to foaming. Use 10 to 25 m /rrf for volume < 150 L. Enzyme membrane reactor Power 10 kW/m maximum volume 0.5 m . Membrane allows diffusion of gas into the liquid without having to use bubbles. 

Fermentation broths are suspensions of microbial cells in a culture media. Although we need not consider the enhancement factor E for respiration reactions (as noted above), the physical presence per se of microbial cells in the broth will affect the k a values in bubbling-type fermentors. The rates of oxygen absorption into aqueous suspensions of sterilized yeast cells were measured in (i) an unaerated stirred tank with a known free gas-liquid interfacial area (ii) a bubble column and (iii) an aerated stirred tank [6]. Data acquired with scheme (i) showed that the A l values were only minimally affected by the presence of cells, whereas for schemes (ii) and (iii), the gas holdup and k a values were decreased somewhat with increasing cell concentrations, because of smaller a due to increased bubble sizes. 

Nozzles, rotors and baff les are patented designs. Field experiments indicate that these designs can be expected to have removal efficiencies of about 50% per cell, Each cell is designed for about 1-rnin retention time to allow gas bubbles to break free of the liquid and form the froth at the surface. Cell dimension and flowrate criteria vary somewhat between manufacturers... 

To run a spectrum of a neat liquid (free of water) remove a demountable cell (Fig. 3) from the desiccator and place a drop of the liquid between the salt plates, press the plates together to remove any air bubbles, and add the top rubber gasket and metal top plate. Next, put on all four of the nuts and gently tighten them to apply an even pressure to the top plate. Place the cell in the sample compartment (nearest the front of the spectrometer) and run the spectrum. 

In the first alternative, if the terminal rise velocity of gas bubbles is known (or can be estimated with confidence), the top surface of the dispersion may be defined as an inlet . Normal liquid velocity may be set to zero while normal gas velocity may be set to terminal rise velocity. The implicit assumption here is that gas bubbles escape the dispersion with terminal rise velocity. It should be noted that even after defining the top surface as an inlet, gas volume fraction at the top surface is a free variable. There is no implicit forcing of gas volume fraction distribution. Alternatively, the top surface of the dispersion can be modeled as a no shear wall. This will automatically set normal liquid velocity to zero. It will also set normal gas velocity to zero. In order to represent escaping gas bubbles, an appropriate sink may be defined for all the computational cells attached to the top surface (Figure 11.7) ... 

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