Area per unit volume , interfacial

2) The oxygen is dissolved in a saturator in a perfluoro-hydrocarbon, which is circulated through the fermenter, in which oxygen is released into the aqueous material system in accordance with the difference in oxygen solubility (see Section 4.8). 

The volume-related interfacial area a in the G/L system depends in two ways upon the bubble size on the one hand, it increases for a given gas throughput as the bubble size becomes smaller, and on the other hand, because small gas bubbles in the liquid rise more slowly and thus result in a larger gas hold-up. 

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Direct photography of drops in done with the use of fiber optic probes using either direct or reflected light. StiU or video pictures can be obtained for detailed analysis. The light transmittance method uses three components a light source to provide a uniform collimated beam, a sensitive light detector, and an electronic circuit to measure the amplified output of the detector. The ratio of incident light intensity to transmitted intensity is related to interfacial area per unit volume. 

R is rate of reaction per unit area, a is interfacial area per unit volume, S is solubiHty of solute in continuous phase, D is diffusivity of solute, k is rate constant, kj is mass-transfer coefficient, is concentration of reactive species, and Z is stoichiometric coefficient. When Dk is considerably greater (10 times) than Ra = aS Dk. 

According to this method, it is not necessaiy to investigate the kinetics of the chemical reactions in detail, nor is it necessary to determine the solubihties or the diffusivities of the various reactants in their unreacted forms. To use the method for scaling up, it is necessaiy independently to obtain data on the values of the interfacial area per unit volume a and the physical mass-transfer coefficient /c for the commercial packed tower. Once these data have been measured and tabulated, they can be used directly for scahng up the experimental laboratory data for any new chemic ly reac ting system. 

Principles of Rigorous Absorber Design Danckwerts and Alper [Trans. Tn.st. Chem. Eng., 53, 34 (1975)] have shown that when adequate data are available for the Idnetic-reaciion-rate coefficients, the mass-transfer coefficients fcc and /c , the effective interfacial area per unit volume a, the physical solubility or Henry s-law constants, and the effective diffusivities of the various reactants, then the design of a packed tower can be calculated from first principles with considerable precision. 

The interfacial area per unit volume and a = AN is incorporated into (3.11.7) ... 

Kl is the mass transfer coefficient for the L phase (m/s), a is the interfacial area per unit volume (m /m ), referred to the total liquid volume of the extractor, V is the total holdup of the tank, and is equal to (Vl+Vq). X is the equilibrium concentration, corresponding to concentration Y, given by... 

Stacks of horizontal, parallel, plates are used in some proprietary decanter designs to increase the interfacial area per unit volume and to reduce turbulence. They, in effect, convert the decanter volume into several smaller separators connected in parallel. 

Aj = interfacial area per unit volume (m2-m 3) Chi = concentration of Component i at the interface (kmol m-3)... 

Liquid-phase mass transfer coefficient Gas-liquid interfacial area per unit volume of dispersion Gas volume fraction in dispersion Diffusivity of cyanogen in solution Henry law coefficient... 

Of course, when designing reactors it is interesting to refer to the specific contact area a (m2 mG+L-3) - that is, the interfacial area per unit volume of gas-... 

In some cases, it can be useful to use other definitions for the specific contact area. For example, some authors use oL, which is the interfacial area per unit volume of liquid (m2 mf3) or aG, the interfacial area per unit volume of gas (m2 mG3). Note that the nomenclature a, aL or oG is not always specified. The specific contact areas are related by ... 

Two immiscible fluids, in contact with each other, share a common surface, called the interface. Operations involving transfer of matter or of heat across an interface are very common in chemical industry. In such operations a large interfacial area per unit volume is necessary if the desired transfer is to be obtained rapidly in equipment of finite size. Three common methods of providing a high ratio of interfacial area to volume are now discussed. 

Figure 12.18 illustrates the conditions that occur during the steady operation of a countercurrent gas-liquid absorption tower. It is convenient to express the concentration of the streams in terms of moles of solute gas per mole of inert gas in the gas phase, and as moles of solute gas per mole of solute free liquid in the liquid phase. The actual area of interface between the two phases is not known, and the term a is introduced as the interfacial area per unit volume of the column. On this basis the general equation, 12.13,... 

Interfacial area. The interfacial area per unit volume of tower, or specific area, is... 

The main benefits of nondispersive solvent extraction over the conventional process are (1) it avoids the need of a settling stage for phase disengagement and the consequent risk of dispersed phase carryover (2) the value of the interfacial area per unit volume can be much higher than in a liquid-liquid dispersion as there is no risk of phase inversion and (3) the interfacial area is easily calculated and scale-up of the process is straightforward. 

In many types of equipment used for gas—liquid reactions, the interfacial area available for mass transfer cannot be determined. The experimentally determined rates of mass transfer are therefore usually reported in terms of transfer coefficients based on unit volume of apparatus rather than on unit interfacial area. These volumetric coefficients are denoted by Kia, Kia, k fi and k[a where a is the interfacial area per unit volume of the equipment. 

In mass-transfer correlations, the volumetric mass-transfer coefficient is expressed using the gas-liquid interfacial area per unit volume of slurry (or expanded column or reactor, VR) (Koide, 1996 Kantarci el al., 2005 NTIS, 1983) ... 

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