Bubbling Buoyancy effect

The buoyancy effect—Being lighter than liquid, the bubble slips through the adjacent liquid that flows downstream. 

In a vertical upward gas-liquid flow, a continuous swarm of bubbles flows upward with the liquid stream due to a buoyancy effect, and the gas slips past the liquid with a relative velocity U0 (rise velocity) ... 

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

Liquid drops suspended in a gas well will settle out" or move toward the earth. If gas bubbles are suspended in a liquid they will rise or move away from the center of the earth due to the buoyancy effect of the liquid. The velocity of the drop or bubble movement is determined by the same physical factors. 

Equations (14-206) and (14-207) result from a balance of bubble buoyancy against interfacial tension. They include no inertia or viscosity effects. At low bubbling rates (carbon tetrachloride for vertically oriented orifices with 0.004 < D < 0.95 cm. If the orifice diameter becomes too large, the bubble diameter will be smaller than the orifice diameter, as predicted by Eq. (14-206), and instability results consequently, stable, stationary bubbles cannot be producecl. 

Retardation of the surface of the film between particle and bubble under the effect of DAL exerts an opposite effect on h. Such paired effects of the DAL is possible only if a surfactant fulfils the condition (8.71). Such surfactants can also effect on h twice. If the surfactant concentration is low also the surface concentration on the leading bubble surface is low. For the same reason the DAL does not determine the retardation of the surface film but affects h only through the bubble buoyancy velocity. The effect of each surfactant on the mobility of the leading bubble surface as a function of concentration and surface activity can be evaluated from the data given in Fig. 8.2. 

The PBWFR concept [XXVII-1] is an evolution of the concept of a direct contact Pb-Bi fast breeder reactor (PBWR) proposed in [XXVII-2]. It is a pressure vessel type reactor, in which sub-cooled water is fed into the hot Pb-Bi coolant above the core, resulting in a direct contact boiling, as shown in Fig. XXVII-1. Boiling bubbles rise due to buoyancy effect, which also works as a lift pump for Pb-Bi circulation. The generated steam passes through the separator and the dryer to remove Pb-Bi droplets, and then flows to the turbine-generator plant. The outlet steam is superheated by 10°C to avoid the accumulation of condensate on a free Pb-Bi surface in the reactor vessel. 

The rate of energy input to the bath E = lie), which is actually contributes to the mixing process, is the sum of the rate of energy input due to buoyancy effect of rising bubble ( b = 11 b) and a fraction of the rate of total kinetic energy associated with the gas at the nozzle exit ( k = llek). Thus,... 

Once issued from the fiber tip, the bubble rises because of buoyancy and grows because CO2 gas diffuses into the bubble. Expansion as a bubble rises to lower pressure also contributes to the bubble size increase, but the effect is negligible in the case of champagne and beer bubbles. To understand the ascent dynamics, it is necessary to know the viscosity of beer and champagne. Beer viscosity depends on its sugar content. A typical viscosity of beer is about 1.44 times that of pure water (Zhang and Xu, 2008). If the temperature is 9°C, the viscosity is 0.0019 Pa s. The ascent velocity of a bubble depends on its size (the specific size limit is based on the physical property of beer) as follows ... 

Most of the features of the theoretical treatment of bubble motion are present in the treatment that considers the water incompressible and neglects gravity effects. We quote from Cole (Ref 1, Chapt 8) The simplest approximation to the true motion of the bas bubble is the one in which it is assumed that the motion of the surrounding water is entirely radial and there is no vertical migration. In this approximation, which has been discussed by a number of writers, the hydrostatic buoyance resulting from differences in hydrostatic pressure at different depths is neglected. It is thus assumed that at an infinite distance from the bubble in any direction the pressure has the same value as the initial hydrostatic pressure P0 at the depth of the charge... 

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