Electroresistivity probe

The electroresistivity probe, recently proposed by Burgess and Calder-bank (B32, B33) for the measurement of bubble properties in bubble dispersions, is a very promising apparatus. A three-dimensional resistivity probe with five channels was designed in order to sense the bubble approach angle, as well as to measure bubble size and velocity in sieve tray froths. This probe system accepts only bubbles whose location and direction coincide with the vertical probe axis, the discrimination function being achieved with the aid of an on-line computer which receives signals from five channels communicating with the probe array. Gas holdup, gas-flow specific interfacial area, and even gas and liquid-side mass-transfer efficiencies have been calculated directly from the local measured distributions of bubble size and velocity. The derived values of the disper-... 

Rigby GR, Van Blockland GP, Park WH, Capes CE. Properties of bubbles in three-phase fluidized beds as measured by an electroresistivity probe. Chem Eng Sd 25 1729-1741, 1970. 

Gas holdup and bubble frequency can be measured with a single-needle electroresistivity probe, while a two-needle probe is required for mean bubble rising velocity... 

Figure 1.2 shows a schematic of the output signals of a two-needle electroresistivity probe. The aforementioned four quantities can be determined from the following relations ... 

Iguchi M, Kawabata H, Nakajima K, MoritaZ (1995) Measurement of bubble characteristics in a molten iron bath at 1600°C using an electroresistivity probe. Metall Mater Trans B 26 67-74... 

Iguchi M, Nakatani T, Kawabata H (1997) Development of a multmeedle electroresistivity probe for measuring bubble characteristics in molten metal baths. Metall Mater Trans B 28 409-416... 

Gas holdup a, bubble frequency /b, mean bubble rising velocity b, and mean bubble chord length Lb were measured using a two-needle electroresistivity probe (not shown in Fig. 2.1). The vertical distance between the tips of the two electrode needles was set at 2 mm. The output signals of the electroresistivity probe system... 

Electroresistivity probe measurements were carried out on the centerline of the bubbling jet at equal intervals of 1 cm. Also, the radial distributions of the bubble characteristics were measured at four representative axial positions of z = 1.5,4.0, 7.0, and 10.0 cm. The experimental results were compared with empirical relations proposed previously by Iguchi et al. [6,7] for an arbitrary combination of metal and gas and with those proposed by Xie et al. [23] for a molten Wood s metal-Na system. 

The cross-section of bubbles was observed using a multi-needle electroresistivity probe [25]. The bubbles have a cross-section illustrated in Fig. 2.23, and could be classified into the well-known skirted type. This kind of bubble appears when the following modified Weber number, Wem, and the Reynolds number, RCm, are relatively small [41]. 

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 ... 

The bubble characteristics represented by the bubble frequency, gas holdup, mean bubble rising velocity, and mean bubble chord length were measured at z = 0.050, 0.100, 0.150, and 0.190m with a two-needle electroresistivity probe [14-20]. The inner and outer diameters of the nozzle were 2.0 x 10 and 4.0 x 10 m, respectively, and the distance 7 was 2 x 10 m. The gas flow rate gg was 41.4 X 10 , lOOx 10 , or 293x 10 m /s. Although the measurements were carried out in the r, 9, and z directions, the results obtained on the r — z plane (9 = 0) will be primarily presented to discuss the Coanda effect on an air-water bubbling jet rising near the side wall of a cylindrical vessel. 

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 ... 

In order to compare the experimental results for dual nozzle gas injection system, the two nozzles are removed, and subsequently gas is injected through a single-hole nozzle of inner diameter of 2.0 x 10 m. The center of the nozzle exit is placed at the origin of the coordinate system. The air flow rate is set to 80 x 10 m /s, being equal to the sum of ggi and 0g2. The center of the nozzle is placed at the vertical axis of the vessel. Bubble characteristics represented by gas holdup a, bubble frequency /b, mean bubble rising velocity b, and mean bubble chord length Lb are measured by making use of a two-needle electroresistivity probe [23,37]. 

A number of water model experiments have been performed on the distributions of water droplets in a thick silicone oil layer using a two-needle electroresistivity probe [8]. The density ratio of the silicone oil to water was 0.93, which differs markedly from 0.4 to 0.5 in the real refining processes. Therefore, similarity condition may not be fully satisfied in these experiments. 

An electroresistivity probe cannot be used to measure the holdup of aqueous ZnCl2 solution droplets in silicone oil because of the low electrical conductivity of aqueous ZnCh solution. A suction pipe method was therefore employed in which holdup was defined as the volumetric ratio of the solution to the total volume of a mixture of the solution and silicone oil. The inherent error in the suction pipe technique was determined by applying an electroresistivity probe and the suction pipe simultaneously to a water-silicone oil system [12]. It was found to be within 7%. 

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