Liquid flow characteristics

In this section, data will be given on the mean velocity and turbulence components of water flow in and near an air-water bubbling jet subjected to the Coanda effect, measured with a two-channel laser Doppler velocimeter. These quantities are closely associated with mixing in metallurgical reactors and the erosion of the side wall of the reactors [22], Particular attention is paid to whether or not the horizontal distributions of the liquid flow characteristics near the side wall are similar in the vertical region above the attachment position. 

The experimental apparatus has been described in Sect. 3.2.2. The electroresistivity probe was removed and a two-channel laser Doppler velocimeter was set up to measure the three velocity components of water flow in the bath. The origin of the cylindrical coordinates (z, r, 9) was placed at the center of the bath, as shown in Fig. 3.3. The velocity components were designated by u, v, and w, respectively. The components, u and v, were measured in the z — r plane including the centerline of the bath and the center of the nozzle exit [21,23]. Digitized velocity data were decomposed into the mean velocity and turbulence components as follows  

The over-bar and prime denote the mean velocity and turbulence components, respectively, N is the number of data points, and the subscript i designates the i th digitized datum. 

Velocity measurements were carried out at four fixed vertical positions (z = 0.05, 0.10, 0.15, and 0.19m) for three gas flow rates = 41.4 x 10 , 100 x 10 , and 293 x 10 m /s just like the measurements of bubble characteristics [22]. The root mean square (rms) values of the axial and radial turbulence components, u rms and i/rms. and the Reynolds shear stress V were calculated from the following equations  

The experimental results for Qg = 41.4 x 10 m /s are presented to illustrate the appearance of the Coanda effect. In Fig. 3.22, a peak occurs in every horizontal 

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The gas-liquid flow characteristics of stirred vessels depend both on the level of agitation and the rate of gas flow and can vary from the case of bubble column type operation to that of a full circulating tank, as shown in Fig. 5.123. The mixing characteristics and gas distribution obtained, obviously exert a considerable influence on the rate of mass transfer obtained (Harnby et al., 1985). 

To improve the multi-phase, particularly liquid, flow characteristics, an MPL can be added and placed between the GDL and CL. This layer is composed of carbon black powder with a fine pore structure. Studies have shown that adding... 

Iguchi M, Ueda H, Uemura T (1995) Bubble and liquid flow characteristics in a vertical bubbling jet. Int J Multiphase Flow 21 861-873... 

Compared with the bubble characteristics, the information on the liquid flow characteristics specified by the axial and radial mean velocities, u and v, the root-mean-square values of the axial and radial turbulence components, m and the Reynolds shear stress u V, and higher correlations of turbulence components, such as the skewness and flatness factors, are limited except for a water-air system [8-12]. 

In general, precise measurements of the liquid flow characteristics in a molten metal bath at high temperatures are very difficult. At present, the mean velocity can be measured under limited conditions by using reaction probes [13-16] andKarman... 

Numerical simulation techniques therefore have acted as a bridge between water models and actual processes [ 19,20], The aforementioned liquid flow characteristics in a molten metal bath agitated by gas injection were predicted numerically by using turbulence models, such as the A — e model, developed originally for single-phase flows [19,20], Numerical results thus obtained, however, have not received reliable experimental confirmation even for mercury and Wood s metal flows. 

In this section, a description is provided of the bubble and liquid flow characteristics measured in a molten Wood s metal bath stirred by bottomhelium gas injection. The aim is to provide experimental data for judging the adequacy of numerical results and to examine whether the results of liquid flow characteristics obtained for a water-air system are useful to predict molten metal flows. 

The bubble and liquid flow characteristics in a molten Wood s metal bath agitated by bottom Helium gas injection measured using a two-needle electroresistivity probe and a magnet probe, respectively, can be summarized as follows ... 

Iguchi M, Tokunaga H, Tatemichi H (1997) Bubble and liquid flow characteristics in a wood s metal bath stirred by bottom helium gas injection. Metall Mater Trans B 28B 1053-1061... 

The liquid flow characteristics specified, for example, by the mean velocity components, the rms values of the turbulence components, and the Reynolds shear stresses are nearly independent of the mean diameter of bubbles provided that the gas flow rate is the same [43]. The same will be shown to be true for the merged bubbling jet. That is, the liquid flow characteristics in the merged jet are not dependent on the bubble diameters. Therefore, if the merging distance. He, is much smaller than the bath depth, Hi, dual nozzle gas injections would not be useful for the enhancement of mixing in the baths. 

Iguchi M, Sasaki K (1999) Coanda effect on liquid flow characteristics in a bubbling jet rising near the side wall of a cylindrical vessel. ISIJ Int 39 213-218... 

Sasaki K, Iguchi M (1999) Bubble and liquid flow characteristics in interacting two water-air vertical bubbling jets in a cylindrical vessel. Tetsu-to-Hagane 85 432-438... 

Very little is iaiown about the effects of wettability of a plate on bubble and molten metal flow characteristics except for the frequency of bubble formation, /b [20-22], These studies have shown that the frequency of bubble formation from a single-hole nozzle or a porous nozzle that is not wetted by the liquid is significantly different from that from a single-hole nozzle of good wettability. This result suggests that the bubble and liquid flow characteristics near a vertical flat plate would... 

Iguchi M, Sasaki K, Nakamura K, Takahashi K (1997) Model study on bubble and liquid flow characteristics in a bottom blown bath with a thick slag layer. CAMP-ISIJ 10 915... 

Accompanied with rapid development of MEMS technologies, micromachining techniques have been increasingly employed in the integration of microfluidic devices. The liquid flow characteristics in microchannels are important in the design and the process control of MEMS and microfluidic devices. 

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