Study bubble

Both the bubble departure frequency / and the number of nucleation centers n are difficult to evaluate. These quantities are known to be dependent on the magnitude of the heat flux, material of construction of the tube, roughness of the inside wall, liquid velocity, and degree of superheat in the liquid elements closest to the tube wall. Koumoutsos et al. (K2) have studied bubble departure in forced-convection boiling, and have formulated an equation for calculating bubble departure size as a function of liquid velocity. 

The simulation results on bubble velocities, bubble shapes, and their fluctuation shown in Fig. 3 are consistent with the existing correlations (Fan and Tsuchiya, 1990) and experimental results obtained in this study. Bubble rise experiments were conducted in a 4 cm x 4 cm Plexiglas bubble column under the same operating conditions as those of the simulations. Air and tap water were used as the gas and liquid phases, respectively. Gas is introduced through a 6 mm nozzle. Note that water contamination would alter the bubble-rise properties in the surface tension dominated regime. In ambient conditions, this regime covers the equivalent bubble diameters from 0.8 to 4mm (Fan and Tsuchiya, 1990). All the air-water experiments and simulations of this study are carried out under the condition where most equivalent bubble diameters exceed... 

A similar technique, different in detail, has been employed by Harrison and Leung (H3) for studying bubble formation in fluidized beds. 

A considerable amount of contradiction exists regarding the influence of this variable. Schurmann (S6), while studying bubble formation in various liquids from porous earthenware, concluded that viscosity is the principal factor which determines the bubble volume. Similar conclusions have been drawn by Davidson and Schuler (D8), who find that an increase in viscosity causes a marked increase in the bubble size. 

The study of bubble formation in non-Newtonian fluids has not been reported in literature in spite of the great industrial uses of these fluids. Recently, Subramaniyan and Kumar (S16) have studied bubble formation under constant flow conditions in fluids following the Ostwald-de-Waele rheological model. The model of Kumar and Kuloor (K16, K18, K19) has been extended to take into consideration the drag variation caused by the complexity of the rheological equation. 

Gas bubbles in liquid metals and in fluidized beds have been the subject of special studies because of their practical importance and because of the experimental difficulties associated with studying bubble properties in opaque media. Much of the work has been carried out in so-called two-dimensional columns, where a sheet of liquid or fluidized particles, typically 1 cm thick, is confined between two parallel transparent walls. Bubbles span the gap between the front and rear faces and can be observed with backlighting. 

The following physical properties can be determined from the results of a black oil reservoir fluid study bubble-point pressure, formation volume factor of oil, solution gas-oil ratio, total formation volume factor, coefficient of isothermal compressibility of oil, and oil viscosity,... 

Our previous studies have clearly shown that two-fluid models are able to capture much of the complex system behavior featured by gas fluidized beds. For example, Kuipers et al. (1991) and Nieuwland et al. (1996a) studied bubble forma-... 

Nieuwland etal. (1995) studied bubble formation at a single orifice in a 2D gas fluidized bed operated at elevated pressure and found very good agreement between theory (two-fluid simulations) and experiment. Similar results were ob-... 

In the Westinghouse electrochemical step, hydrogen is released at the cathode interface. In the numerical study, bubble generation is assumed to be localized in the first row of fluid cells neighbouring the electrode. In this special zone analogue to a boundary layer, the rate of gas production is assumed equal to the rate of the reduction process. It is modelled by the source term S2 of the dispersed phase mass-balance equation, assuming a 100% Faradic yield. 

Wang and Tabereaux [42] too used cell voltage fluctuations (for a 15-cm diameter anode) to study bubble release. Figure 18 shows the voltage trace for an anode after... 

Kariyasaki [70] studied bubbles, drops, and solid particles in linear shear flow experimentally, and showed that the lift force on a deformable particle is opposite to that on a rigid sphere. For particle Reynolds numbers between 10 and 8 the drag coefficient could be estimated by Stokes law. The terminal velocity was determined to be equal to that of a particle moving in a quiescent... 

As we shall see, microradiology with coherent x-rays is very effective for studying bubbles. This is important since the role of hydrogen and hydrogen bubbles in electrodeposition is relevant but still controversial. 

Klausner [34] studied bubble nucleation in stratified flow of refrigerant R113 in a horizontal rectangular channel. The nucleation site density decreased with increasing vapor velocity as illustrated in Fig. 15.15 at a velocity of around 5 m/s, nucleation was totally supressed. Klausner et al. interpreted their data in terms of the relationship between critical radius of nucleation site rc and number density the data from this interpretation are shown in Fig. 15.16 and it will be seen, that for these particular conditions, a rather narrow range of site radius applied. The question of suppression of nucleate boiling is discussed further later in this chapter. 

The terms fining and refining refer to the removal of gaseous inclusions, or bubbles, from the melt. Although the presence of bubbles in a glass sample is not necessarily detrimental for many scientific studies, bubbles are definitely undesirable in most commercial glasses. Bubbles in commercial products are almost always considered flaws and result in rejection of the product. These gas-filled inclusions may occur as very small spheres (< 0.4 mm diameter), which are frequently called seed... 

Novel bubble-induced flow designs apply a plethora of mechanisms that help differentiate each specific design from other novel and standard devices. Some changes are structural and include use of different materials and internals. Others include the use of novel methods to excite the bubble interface and induce gas-liquid mass transfer. Novel methods exclude devices that are created to study specific events relating to standard devices. For example, the study by Sotiriadis et al. (2005) using a specially designed bubble column where the phases move downward to specifically study bubble behavior, bubble size, and gas-liquid mass transfer in the downcomer of airhft reactors would fall in the excluded devices. 

Koide and coworkers (27) studied bubble sizes in coalescing media (water) and noncoalescing solutions of alcohols and electrolytes and proposed empirical correlations which involve modified Froude and Weber numbers. However, Schiigerl et al, (16) have shown that the agreement is only sufficient for water and methanol solutions, Solutions of ethanol show large deviations which cannot be explained by surface tension veriation. 

Among these, the first two case studies describe invariable coupling whereas the third one is devoted to variable coupling. The piston example demonstrates the usefulness of a thermodynamical approach in this mechanical domain and outlines the difference between a global pressure and a local pressure. In the ion distribution, the exponential function ruling the capacitive relationship in physical chemistry and corpuscular domain is exported to the electrodynamical domain. The last case study Bubble introduces the surface energy variety and demonstrates the Laplace law in capillarity. 

It is noted that the pressure effects on the heat transfer coefficient are different between large-particle and small-partiele systems (Luo et al., 1997a Yang et al., 2000b). Similar observations were also found for hydrodynamics and bubble characteristics between large-particle and small-particle systems. Luewisutthichat et al. (1997) photographically studied bubble characteristics in multiphase flow systems. They found that large-particle systems (i.e., three-phase fluidized beds) exhibit appreciably different... 

Most of the instruments allow only the measurement of surface and interfacial tensions, without a sufficient control of the drop/bubble size. Advanced models provide very accurate controlling procedures. The instrument described here in detail represents the state of the art of drop and bubble shape tensiometers. The possibility to study bubbles in addition to drops opens a number of features not available by other instruments less loss of molecules caused by adsorption from extremely diluted solutions (small reservoir in the small single drop), long time experiments with very small amounts of a sample, easy application of a pressure sensor for additional measurement of the capillary pressure inside the bubble. Moreover, high quality sinusoidal relaxation studies can be performed by inserting a piezo system which can be driven such that very smooth changes of the bubble surface area are obtained. 

Davidson and Harrison [48] have studied bubbling phenomena in fluidized beds extensively and have shown that the rising velocity of gas bubbles in fluidized beds may be estimated with the aid of the Davies and Taylor equation, which was originally developed for the rise of large (spherical cap) gas bubbles in liquids ... 

Bai et al (2012) have carried out DBM simulations to computationally measure the key quantities of the bubbly flow in a square bubble column in terms of the turbulent liquid dispersion coefficient. This was done by releasing two sets of neutrally buoyant tracer particles in the fiquid phase and recording their dispersion with time one at the top of the column (tracer 0) and one set at the bottom. It was found that with increasing superficial gas velocity, the dynamics of the liquid in the column is enhanced, and hence the turbulent dispersion coefficient increases. The obtained dispersion coefficients are shown in Fig. 8 and are well within the spread of literature correlations. Note that this spread can be attributed to differences in geometry of the studied bubble columns. The power of the DBM is that it accounts for the details of the geometry and thereby provides a predictive capability that is hard to match when using empirical correlations. 

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