Oxygen transfer coefficient, influence

With regard to the liqiiid-phase mass-transfer coefficient, Whitney and Vivian found that the effect of temperature upon coiild be explained entirely by variations in the liquid-phase viscosity and diffusion coefficient with temperature. Similarly, the oxygen-desorption data of Sherwood and Holloway [Trans. Am. Jnst. Chem. Eng., 36, 39 (1940)] show that the influence of temperature upon Hl can be explained by the effects of temperature upon the liquid-phase viscosity and diffusion coefficients. 

In fact none of these models of the mass-transfer coefficient are of much use for the calculation of Kia values in small scale reactor conditions and we have to obtain them by experiments. However, these models can be used as a guide to estimate the influence of the physical properties of the medium. They also make it possible to consider relative values of Ka for compounds for which in experiments the value of Ka is not measurable as easily as for gases such as oxygen. 

In Fig. 2 the key parameters are presented for recombinant E. coli batch cultivation in a 60-1 working volume airUft tower loop reactor at constant aeration rate up to 16 h, whereupon the temperature was increased from 30 to 42 °C and gene expression was induced. At the same time concentrated Luxia-Bertani (LB) medium was added to the reactor. To avoid oxygen limitation, the aeration rate was increased (Fig. 2 a). At 12 h the foaming increased and SE9 was added to the medium. The bubble velocities (Fig. 2b) and the specific gas/liquid interfacial area (Fig. 2 c) quickly increased and passed a narrow maximum, but kLa dropped and the OTR was not influenced (Fig. 2d). After the induction of the gene expression by a temperature increase and medium supplement the dissolved oxygen concentration with respect to the saturation increased due to the elevation of the aeration rate (Fig. 2 a) the mean bubble velocity (Fig. 2 b) and specific interfacial area (Fig. 2 c) decreased, OTR increased and kLa remained at low values (Fig. 2d). The mass transfer coefficient with respect to the liquid phase kL dropped from about 1.67 to 0.67 ms after the addition of SE9 to the medium [51]. 

The cell growth rate, yXi, can mainly be influenced by the volumetric mass transfer coefficient, kj a, and yield coefficient, x/Q Since the oxygen transfer rate, kra i, is independent of D, one can reduce eq. (74) for cell-free feed and steady-state operation ... 

Two-phase system properties can strongly influence cultivation conditions, especially if growth is oxygen transfer limited. To treat the oxygen transfer rate quantitatively it is necessary to determine the volumetric mass transfer coefficient, kj a, the dissolved oxygen concentration in t e liquid bulk. Op, and at the gas liquid interface. Op. The specific interfacial area is influenced by the Sauter bubble dieuneter, dg, and the relative gas holdup, e q, according to eq. (ToO) ... 

With an aerobic bioprocess it is evident that, in addition to substrate, O2 can be rate limiting. The curve for biomass concentration increasing with time in a batch run is significantly influenced by the oxygen transfer rate quantified by the volumetric transfer coefficient This situation of an external... 

It is possible to influence the size of the dispersion spots in liquid-gas systems (specific phase contact surface) and therefore, the mass transfer efficiency, by changing the method of reactant introduction. During the motion of the gas-liquid flows in tubular turbulent reactors, an increase of the gas supply branch pipe diameter results in a slight decrease of the sulfite number of the reactor (Table 4.4), which can be seen from the decrease of the phase contact surface as d 2 grows by 15%. Similarly, with the decrease of the coaxial liquid-phase supply branch pipe diameter from 10 to 5 mm, SuR equals 13.5 and 14 g02/h, respectively. Thus, there is almost no dependence of the rate of sodium sulfite oxidation in aqueous solution, by atmospheric oxygen, on the method of reactant introduction. This is related to the fact that changes in the method of the liquid- and gas-phase introduction, in particular, the diameters of the feeding branch pipes, do not influence the mass delivery coefficient in the liquid phase. 

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