Holdup measurement

Viswanathan et al. (V6) measured gas holdup in fluidized beds of quartz particles of 0.649- and 0.928-mm mean diameter and glass beads of 4-mm diameter. The fluid media were air and water. Holdup measurements were also carried out for air-water systems free of solids in order to evaluate the influence of the solid particles. It was found that the gas holdup of a bed of 4-mm particles was higher than that of a solids-free system, whereas the gas holdup in a bed of 0.649- or 0.928-mm particles was lower than that of a solids-free system. An attempt was made to correlate the gas holdup data for gas-liquid fluidized beds using a mathematical model for two-phase gas-liquid systems proposed by Bankoff (B4). 

Inglezakis, V.J., Zorpas, A.A., Grigoropoulou, H.P., Arapoglou, D., Liquid holdup measurements using tracing techniques in zeolite packed beds, 5th International Scientific and Technical Conference Water Supply and Water Quality, Poznan, Poland, 430-440 (2002)... 

HI la. Hewitt, G. F., and Lovegrove, P. C., Comparative film thickness and holdup measurements in vertical annular flow. At. Energy Res. Estab. (Gt. Brit.) Harwell, Memo M-1203 (1963). 

A gamma-ray transmission technique was used by Calderbank (1958) to determine the point gas holdup. The application to holdup measurements depends on the relationship... 

Table I. Experimental conditions for average gas holdup measurements. (Gas phase is nitrogen)...

Experimental values of the total liquid holdup were obtained by simultaneous closure of the inlet and exit solenoid valves, followed by drainage over a 15-min period. In some experiments, these values were checked by actual weighing of the section of the column in between the solenoid valves. The liquid holdup data were obtained by correlating the conductivity to the liquid/gas ratio. The details of the liquid holdup measurement technique are given in the Pittsburgh Energy Research Center s quarterly reports.22... 

The y-ray transmission technique has been used to determine the point holdup of gas in mechanically agitated tanks by Calderbank (Cl) in plate columns by Calderbank and Rennie (C4), Vinokur and Dil man (VIO), Macmillan (M3), and Bernard and Sargent (B17) and in packed columns by Eisenklam and Ford (E2), Hwa and Beckmann (H14), and Saada (Si). The application of y-ray absorption to holdup measurements is based on the relationship... 

Al-Dahhan, M.H. Highfill, W. Liquid holdup measurement techniques in laboratory high pressure trickle bed reactors. Can. J. Chem. Eng. 1999, 77, 759. 

The gas holdup measurement based on Eq. (4.11) completely neglects the effects of wall shear stress and has been identified by Tang and Heindel (2006a) as Method... 

Hills, J.H. (1976), The operation of a bubble column at high throughputs. I - Gas holdup measurements, The Chemical Engineering Journal, 12 89-99. 

Thatte, A.R., Ghadge, R.S., Patwardhan, A.W., Joshi, J.B., and Singh, G. (2004), Local gas holdup measurement in sparged and aerated tanks by y-ray attenuation technique, Industrial Engineering Chemistry Research, 43(17) 5389-5399. 

The gamma-ray transmission technique previously employed by Vermeulen et al. (5) has been used to determine the point gas holdup in mechanically agitated tank by Calderbank, in plate columns and in packed columns (I). The principles of the application of gamma-ray absorption to holdup measurements depend on the use of the relationship. 

This correlation reqnires information on u, which can be estimated using Equation 10.7. This latter equation requires data on as a function of superficial gas velocity to evaluate the terminal rise velocity of the bubble, These data can be obtained throngh simple gas holdup measurements. The drift flux model of Zuber and Findlay (1965) can be used to obtain as per Equation 10.10 ... 

Michele V, Hempel DC. Liquid flow and phase holdup— measurement and CFD modeling for two-and three-phase bubble columns. Chem. Eng. Sci. 2002 57 1899-1908. 

Kumar SB, Moslemian D, Dudukovic MP Gas-holdup measurements in bubble columns using computed tomography, AIChE J 43 1414—1425, 1997. http //dx.doi.org/ 10.1002/aic.690430605. 

The "holdup" model assumes that contacting is- proportional to the liquid holdup in the catalyst bed. This model, proposed by Henry and Gilbert [23], uses total holdup measurement as a basis and presupposes that each element of liquid hold-up is associated with an equivalent catalyst element and that all of these equivalences are of equal efficiency without respect to the nature of the reaction. Liquid velocity, particle size and fluid physical property affect contacting only as those parameters affect holdup. 

Equation (10) is valid for a column with an inner diameter of 100 mm and a clear liquid height greater than 1200 mm. In a further step we therefore examined, wether gas holdup is influenced by the column dimensions. In figure 3 gas holdup measurements are plotted versus gas linear velocity. The experiments were carried out in columns with inner dimensions larger than 150 mm and clear liquid heights higher than 1000 mm. Furthermore, the employed gas distributors caused a churn turbulent flow already at low gas throughputs. 

The shape of successively rising bubbles in molten metal baths is closely related to the horizontal distribution of gas holdup, as shown in Fig. 1.3. Thus the shape can be predicted from the results of gas holdup measurements. 

In churn-turbulent flow, in the core of the column the bubble velocity and chord length distributions are alike at different radial positions, but in the wall region they are very different from the core of the column. A few reports on the application of optical fibre probes for phase holdup measurements in three-phase fluidized beds have be found, in which the local bubble frequency, the local phase holdups and the local bed porosity were measured [108, 159, 177]. Time-average local gas holdups and bubble frequency were measured independently by an optical fiber probe. 

Razzak SA, Baighi S, Zhu J-X, Mi Y (2009) Phase holdup measurement in a gas-liquid-solid drculating fluidized bed (GLSCFB) riser using electrical resistance tomography and optical fibre probe. Chem Eng J 147 210-218... 

A2.8.3 Convert the boilup measurement in litres per hour to rates per hour in (mL/h) x cm. Convert also the AP measurements to kPa/m (mm Hg/m) and the holdup measurement to milliliters per theoretical plate. 

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