Bubble injection Diameters

Figure 14 Images obtained by means of laser interferometry showing the behavior of CO2 bubbles injected into ethanol for (a) pure solvent and (b) solvent saturated with CO2 T = 363.15 K, P = 8 MPa, the bubble diameter is about 1.6 mm. The interferometric fringes show intensive mass transfer in the solvent...

Siemes and Weiss (SI4) investigated axial mixing of the liquid phase in a two-phase bubble-column with no net liquid flow. Column diameter was 42 mm and the height of the liquid layer 1400 mm at zero gas flow. Water and air were the fluid media. The experiments were carried out by the injection of a pulse of electrolyte solution at one position in the bed and measurement of the concentration as a function of time at another position. The mixing phenomenon was treated mathematically as a diffusion process. Diffusion coefficients increased markedly with increasing gas velocity, from about 2 cm2/sec at a superficial gas velocity of 1 cm/sec to from 30 to 70 cm2/sec at a velocity of 7 cm/sec. The diffusion coefficient also varied with bubble size, and thus, because of coalescence, with distance from the gas distributor. 

Detection If a small capillary diameter is desired for efficiency purposes, the detection part of the capillary can be adapted for better detection sensitivity. Examples are the bubble cell capillary and the Z-cell. In the bubble cell capillary, the capillary diameter is enlarged at the detection window so that better concentration sensitivity is obtained. If you implement a bubble cell capillary in your pharmaceutical analysis method, it is important to test different batches. Test also whether you need a bubble cell capillary or whether you can gain similar sensitivity increase with a proper injection procedure. Also, check the effect of the bubble cell on band broadening. An approximately three-times sensitivity enhancement is possible. 

Size distribution plays a major role in the microbubble stability, behavior in vivo, and the microbubble acoustic response. The Rayleigh-Plesset equation which describes the microbubble response to pressure waves suggests that ultrasound scattering is proportional to the sixth power of the microbubble diameter [46]. It is not possible, however, to inject large bubbles (e.g., 0.1 or 1 mm in diameter) in the bloodstream, because they would be immediately lodged in the vasculature as emboli, severely limiting the blood flow. Fortunately, microbubbles with the size of several micrometers are still quite echogenic in the ultrasound... 

Example 12-2 An aqueous solution contains 10 ppm by weight of an organic contaminant af molecular weight 120, which must be removed by air oxidation in a lo-cm-diameter bubble column reactor at 25°C. The liquid flows downward in the tube at an average velocity af 1 cm/sec. The air at 1 atm is admitted at 0.1 liter/sec and is injected as bubbles 1 mm diameter, which rise at 2 cm/sec. Assume no coalescence or breakup and that both gas and liquid are in plug flow. The reaction in the Hquid phase has the stoichiometry A + 2O2 products with a rate C. ... 

Dissolvcd-gax units take a portion ol treated water effluent and saturate it with natural gas in a contactor. The higher the pressure, the more gas that can be dissolved in the water. Most units axe designed for a 2U to 40-psig contact pressure. Normally, 20 to 50% of treated water is rccircu iated for contact with gas. Gas-saturated water is then injected into a flotation tank as shown in Fig. 7. Dissolved gas breaks out of solution in small-diameter bubbles when flow enters the atmospheric flotation chamber. 

Figure 1 is a schematic diagram of the experimental setup. The test section is a horizontal rectangular channel 40 mm in height (H), 160 mm in width (W), and 6,000 mm in length (L). The rectangular channel is completely constructed of transparent acrylic resin, as shown in Figure 2. Tap water and air are used as the gas and liquid phases, respectively. Water is circulated by a 2.2 kW pump fed by a water reservoir 4.2 m away. Air bubbles are injected into the horizontal channel from the upper inner surface of the channel. An array of capillary needles produces bubbles 10-100 mm in length. Before the air and water are mixed, their volumetric flow rates are measured. After leaving the horizontal channel, the gas-liquid mixture is dumped into a tank that acts as a bubble remover when the liquid phase is recirculated it is free of bubbles. At the end of the horizontal channel tracer particles are added to the water to act as ultrasound reflectors. The mean particle diameter is 200 pm and the particle density is 1020 kg/m3. These tracer particles are assumed to...

Devolatilizing Screw Extruder A 150-mm-diameter, square-pitched, single-flighted screw extruder, with screw channel depth of 25 mm and 20-mm flight width is used to devolatilize a 1000-kg/h stream with 0.78-g/cm3 density at 200° C and 125 torr. (a) At what frequency of screw rotation will the channel be 30% or less full (b) With water injection, if density is halved by formation of 1-mm bubbles, how much surface area (per meter length) is created (c) How does... 

These bioreactors are characterized by their large height-to-diameter ratio and by an internal concentric cylinder, as shown in Figure 9.7. In the lower central region, there is a tube that injects gas inside the bioreactor. The pressurized gas stream generates bubbles that result in a low-density region inside the central tube. When these bubbles ascend, the liquid is... 

Bubbling devices can be porous plates, cartridges from glass, ceramics, metal ceramics and plastics, and also various kinds of gauzes. Interesting modification are the elastic plates in which the diameter of their orifices is altered with the pressure of gas injected through them. It... 

In order to reduce the size of bubbles formed by dispersion through filters, additional methods and devices are used, for example, rotating drums [8], horizontally situated filter pores, rotating cylinders causing solution movement [8], shock effects on the bubbles formed [25], round body devices placed over capillary or pore orifice outlet [26]. Very small bubbles can be formed from thin capillaries with diameter up to 10 - 20 im (sometimes up to 4 pm) or very fine filters. However, the rate of foam formation when such capillaries or filters are employed is very low. Simple injection type devices for generating highly dispersed foam... 

Fig. 17. Photographically observed and theoretically calculated bubble growth at a single orifice in a 2D gas fluidized bed. Physical properties of the particles diameter, 500 /im density, 2660 kg/m Bed dimensions width, 0.58 ra height, 1.0 m. Injection velocity through orifice 10.0 m/s.

The influence of wake motion on bulk turbulence induced in the liquid is understood more clearly by inspecting oscillograms which show the fluctuation of local liquid velocity. Figure 43 shows such oscillograms taken by Kikuchi (K30) with a hot-wire probe. The bubble column is 8.0 cm in diameter, water-filled to a 170-cm height, with the probe 115 cm above the bottom gas distributor. In the column bubbles of constant volume (100 cc) are injected successively at constant time intervals, either at 2.1 sec (case a) or 0.50 sec (case b). Case c is an example of continuous bubbling at f/c = 6.45 cm/sec. 

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