Bubble dimension

This section of the programme calculates and displays the variation in the applied acoustic pressure, the resonance pressure (or frequency) and the bubble dimensions with time. The GCOL statements in lines 1200 and 1220 refer to colour (e.g. GCOL0,l is red and GGOL0,3 is white). 

The fermentation tests were carried out in shake flasks, STR and FBR. The effect of the following parameters was investigated the amount of gel and the total cell concentration in the bioreactor the addition of hydrogen acceptor (acetone), instead of air, to activate the electron transport in the respiratory chain and the use of Teflon-made filters as air diffusers to reduce air bubble dimension and increase oxygen solubility. 

Contact angle measurements provide information on the wettability of the sample, the surface energetics of the solid, and the interfacial properties of the solid-liquid interface. The samples were immersed in water and captive air and octane bubbles were determined by measuring the bubble dimensions. By measurement of both air and octane contact angles the surface free energy (.y) of the solid-vapor ( > ) interface may be calculated by use of Young s equation and the narmonic mean hypothesis for separation of the dispersive and polar components of the work of adhesion. This method for determination of surface and interfacial proper-... 

As the dynamic adsorption layer deviates farther fi"om equilibrium, the drop in the surface concentration increases along the surface and leads to the formation of a stagnant cup. The deviation from equilibrium is caused by compressive viscous shear forces and surface convection of adsorbed molecules it grows as the bubble dimensions and velocity increase and it diminishes as the exchange of adsorbed molecules between the solution bulk and surface... 

Due to rapid decrease of the retardation coefficient with increasing bubble dimension, a residual surface mobility remains for big bubbles. The transport stage for sufficiently small bubbles and solid spheres is identical. The characteristic bubble value which describes the boundary between the two ranges of bubble dimensions can be determined from Eq. (10.35) after substitution of Xb as a function of bubble radius, according to Eq. (8.106),... 

When deposition of emulsion drops is investigated, sedimentation can be neglected so that the first term in Eq. (10.27) dominates even at strong retardation. Retardation of the surface becomes less efficient with increasing bubble dimensions and, respectively, Reynolds number. Therefore, the experimental verification of the hypothesis of incomplete retardation of the surface at intermediate Reynolds numbers is of interest. A maximum removal of impurities fi om the water used is important in such experiments. 

Advantageous is a strong decrease of the bubble dimension down to values less than... 

If a exceeds this value, a decrease of bubble size will only decrease the collision efficiency. Large bubbles with the size of the order of a 0.5mm are obtained in usual pneumatic dispersions formed in flotation machines. It is much more diflflcult to obtain bubbles 10 to 50 times smaller, which can be achieved by using completely different methods of bubble generation, electroflotation and air-dissolved flotation. Since a decrease of bubble dimensions is connected with substantial complication and a rise in price of the technology, it is necessary to forecast sufficiently accurately the required size of bubbles as a function of surfactant... 

Fig. 10.9. Dependence of the efficiency of capture of several fractions of quartz particles on their dimensions d and bubble dimensions, d =40.5nm( ), 31.4pm ( ), 27.6pm ( ), 18pm (- ), 12 pm (A), according to Anfruns Kitchener (1976)...

Soluble substances exist which can immobilise the surface even of large bubbles present in water at extremely low concentrations. The problem of the effect of residual mobility of a bubble surface loses its meaning if these impurities are contained in water. However, their influence on surface mobility can be hampered at retarded adsorption kinetics. At a given surface tension decrease due to impurities a critical bubble dimension exists. For bubbles exceeding the critical size a residual surface mobility is present. Eq. (10.40) interrelates the critical bubble size with the surface tension drop. On the basis of Eq. (10.45) it was shown that residual mobility is important even for highly contaminated river water at high Reynolds numbers (cf. Section 10.2.7). 

Polymer chemistry and molecular structure are vital in establishing film properties, but bubble geometry resulting from processing conditions is also significant. Molecular orientation and crystalline structure - controlled by bubble dimensions - affect properties such as tensile strength, impact toughness, and clarity. 

Slug flow The bubble dimensions are close to tube pipe diameter and the bubbles have a characteristic shape similar to a bullet with a hemispherical nose with a blunt tail end. They are commonly referred to as Taylor bubbles after the instability of that name. Taylor bubbles are separated from one another by slugs of liquid, which may include small bubbles. 

In the bubble-film extraction device, the surface-active impurities, dissolved gases, and some ions are removed from the treated water flow. In this case, the physical and chemical properties of impurities, their concentration, the intensity of air bubbling, dimensions of flotation device, sizes of gaseous bubbles, and water flow rate have an influence on the process. 

The rate of removal of surface-active contaminants from treated water using flotation depends upon many factors. In particular, it depends on the surfactant concentration in the water bulk, the magnitude of equilibrium constant of surfactant adsorption at the air-water interface, the adsorption rate of surfactants, air flow, and air bubble dimensions. The analytical equation that relates the volume and the surface concentration of the surfactant in adsorption process is the Langmuir adsorption equation (see Appendix 8.A) ... 

If the bubble dimension is larger and deviates from a spherical shape, a correction factor has to be added to the equation. This correction factor/, available either a as table or as a polynomial equation, is needed only when the capillary radius reap > 0.2 mm. 

Fiber-optical probes of the reflection type (backscattering) has been used to measure local solid volume fraction, local bubble velocity and bubble chord length (vertical bubble dimension) in fluidized bed reactors operating in different flow regimes. 

To establish direct local information and precise bubble dimensions, various probes were used. The electrical resistivity probe was developed to measure the velocity and diameter of a bubble in a conducting liquid medium. In a non-conducting medium, the optical probe is more appropriate. 

F igure 16.10shows the fully developed bubbling characteristics of the two matched units. They are very similar, with bubble dimensions in both cases growing to about half the bed width, giving rise to intense bed surface disruption. 

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