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Slip velocity, measurement

R. P. Fishwick, J.M. Winterbottom, E.H. Stitt, "Explaining Mass Transfer Observations in Multiphase Stirred Reactors Particle-Liquid Slip Velocity Measurements using PEPT", Catalysis Today, 2003, in press. [Pg.160]

It is not possible to calculate the in-line concentrations and slip velocity from purely external measurements on the pipe, i.e. a knowledge of the rates at which the two components are delivered from the end of the pipe provides no evidence for what is happening within the pipe, It is thus necessary to measure one or more of the following variables ... [Pg.199]

The above results show close agreement between the experimental and theoretical friction factor (solid line) in the limiting case of the continuum flow regime. The Knudsen number was varied to determine the influence of rarefaction on the friction factor with ks/H and Ma kept low. The data shows that for Kn < 0.01, the measured friction factor is accurately predicted by the incompressible value. As Kn increased above 0.01, the friction factor was seen to decrease (up to a 50% X as Kn approached 0.15). The experimental friction factor showed agreement within 5% with the first-order slip velocity model. [Pg.43]

The discussion above that led to Eqs. (4.2.6 and 4.2.7) assumes that the no-slip condition at the wall of the pipe holds. There is no such assumption in the theory for the spatially resolved measurements. We have recently used a different technique for spatially resolved measurements, ultrasonic pulsed Doppler velocimetry, to determine both the viscosity and wall slip velocity in a food suspension [2]. From a rheological standpoint, the theoretical underpinnings of the ultrasonic technique are the same as for the MRI technique. Flence, there is no reason in principle why MRI can not be used for similar measurements. [Pg.389]

Hsu, Y. Y, F. F. Simon, and R. W. Graham, 1963, Application of Hot-Wire Anemometry for Two-Phase Flow Measurements Such as Void-Fraction and Slip Velocity, pp. 26-34, ASME Symp. on Multiphase Flow, Philadelphia, PA. (3)... [Pg.538]

Jiang, T.Q., Young, A.C., and Metzner, A.B. "The Rheological Characterization of HPG Gels Measurement of Slip Velocities in Capillary Tubes," Rheol Acta 25 397-404 (1986). [Pg.105]

Fig. 3a indicates that the bubble-rise velocity measured based on the displacement of the top surface of the bubble ( C/bt) quickly increases and approaches the terminal bubble rise velocity in 0.02 s. The small fluctuation of Ubt is caused by numerical instability. The bubble-rise velocity measured based on the displacement of the bottom surface of the bubble (Ubb) fluctuates significantly with time initially and converges to Ubt after 0.25 s. The overshooting of Ubb can reach 45-50 cm/s in Fig. 3a. The fluctuation of Ubb reflects the unsteady oscillation of the bubble due to the wake flow and shedding at the base of the bubble. Although the relative deviation between the simulation results of the 40 X 40 x 80 mesh and 100 x 100 x 200 mesh is notable, the deviation is insignificant between the results of the 80 x 80 x 160 mesh and those of the 100 X 100 x 200 mesh. The agreement with experiments at all resolutions is generally reasonable, although the simulated terminal bubble rise velocities ( 20 cm/s) are slightly lower than the experimental results (21 25 cm/s). A lower bubble-rise velocity obtained from the simulation is expected due to the no-slip condition imposed at the gas-liquid interface, and the finite thickness for the gas-liquid interface employed in the computational scheme. Fig. 3a indicates that the bubble-rise velocity measured based on the displacement of the top surface of the bubble ( C/bt) quickly increases and approaches the terminal bubble rise velocity in 0.02 s. The small fluctuation of Ubt is caused by numerical instability. The bubble-rise velocity measured based on the displacement of the bottom surface of the bubble (Ubb) fluctuates significantly with time initially and converges to Ubt after 0.25 s. The overshooting of Ubb can reach 45-50 cm/s in Fig. 3a. The fluctuation of Ubb reflects the unsteady oscillation of the bubble due to the wake flow and shedding at the base of the bubble. Although the relative deviation between the simulation results of the 40 X 40 x 80 mesh and 100 x 100 x 200 mesh is notable, the deviation is insignificant between the results of the 80 x 80 x 160 mesh and those of the 100 X 100 x 200 mesh. The agreement with experiments at all resolutions is generally reasonable, although the simulated terminal bubble rise velocities ( 20 cm/s) are slightly lower than the experimental results (21 25 cm/s). A lower bubble-rise velocity obtained from the simulation is expected due to the no-slip condition imposed at the gas-liquid interface, and the finite thickness for the gas-liquid interface employed in the computational scheme.
Equation 3.64 shows that the total discharge rate Q that is measured consists of normal, genuine flow given by the integral term, plus the extra discharge due to slip. The slip term is simply the slip velocity v, multiplied by the cross-sectional area of the pipe. [Pg.126]

In order to determine whether slip occurs with a particular material, it is essential to make measurements with tubes of various diameters. In equation 3.66, the value of the integral term is a function of the wall shear stress only. Thus, in the absence of wall slip, the flow characteristic 8 u/dt is a unique function of tw. However, if slip occurs, the term 8vjd will be different for different values of d, at the same value of tu., as shown in Figure 3.11. It is clear from equation 3.66 that for a given value of the slip velocity vs, the effect of slip is greater in tubes of smaller diameter. If the effect of slip is dominant, that is the bulk of the material experiences negligible shearing, then it can be seen from equation 3.66 that on a plot of... [Pg.127]

Having established that wall slip occurs but is not dominant, the procedure is to estimate the value of v, and hence calculate a corrected flow rate by subtracting the slip flow from the measured flow rate. In general it is found that the slip velocity increases with tw and decreases with d, although in some cases vs is independent of dt. Consequently, it can be seen from equation 3.66 that the effect of slip decreases as d, increases, and becomes negligible at very large diameters. [Pg.128]

Liquid metals represent a special case in the estimation of two phase void fractions. Because of the great differences in vapor and liquid density, very low qualities correspond to high void fractions, and for the same reason very large slip velocity ratios occur. In a recent paper. Smith et al. (S13) review previous measurements of void fractions in... [Pg.232]

The design procedure used by Kosters, of Shell Oil Co., who developed this equipment, requires pilot plant measurements on the particular system of HTU and slip velocity as functions of power input. The procedure for scaleup is summarized in Table 14.5, and results of a typical design worked out by Kosters (in Lo et al., 1983, pp. 391-405) are summarized in Example 14.11. Scaleup by this method is said to be reliable in going from 64 mm dia to 4-4.5 m dia. The data of Figure 14.18 are used in this study. [Pg.485]

T.Q. Jiang, A.C. Young and A.B. Metzner, The Rheological Characterization of HPG gels Measurement of slip velocities in capillary tubes, Rheol. Acta, 25 397 (1986). [Pg.305]

The first oil-catalyst contact is essential. The mixing temperature (about 530-600 °C) is very difficult to measure and is about 20-80 °C higher than the riser exit temperature (4, J). The superficial gas velocity at the inlet is several meters per second, much higher than the terminal velocity of the catalyst, which is about 0.20 m/s. The catalyst and the gas are transported upwards together but at a different superficial velocity, u (6). These two velocities are related by the slip velocity (sv), defined as follows ... [Pg.170]

Results. The fuels studied in this program have been described previously, and the ranges of the combustion variables investigated were as follows droplet diameter 66-190 ym, slip velocity 300-1200 cm/sec gas temperature < 1500 K and stoichiometry 0.5 < < 1.5. Initial drop size was determined by the orifice employed in the droplet generator and was verified through the use of LDA/visibility measurements and photography. Slip velocity was calculated as the vector sum of the LDA measured droplet velocity and the hot gas velocity. [Pg.196]

Imafuku et al.46 measured the gas holdup in a batch (i.e., no liquid flow) three-phase fluidized-bed column. They found that the presence of solids caused significant coalescence of bubbles. They correlated the gas holdup with the slip velocity between the gas and liquid. They found that the gas holdup does not depend upon the type of gas distributor or the shape of the bottom of the column when solid particles are completely suspended. Kato et al.53 found that the gas holdup in an air-water-glass sphere system was somewhat less than that of the air-water system and that the larger solid particles showed a somewhat smaller... [Pg.316]

On Fig. 4, a typical curve of the measured slip velocity is reported as a function of the... [Pg.343]

Figure 4. Evolution of the slip velocity. Vs, as a function of the top plate velocity, Vt, for a PDMS melt of molecular weigt 9.6 lO in contact with a silica surface pretreated by grafting an almost dense monolayer of OTS. The two dotted lines are respectively Vj =V, and Vs= VtA/d. Clearly, slip is always present, as indicated by the fact that the measured Vj is always above the average velocity one would have inside a layer of thickness A, in the case of a linear velocity gradient and no slip (lower dotted line). At very high shear rates V, becomes comparable to Vt and the flow is almost a plug flow. The experimental relative uncertainty on Vj is larger for the low slip velocities (close to 20%) than for the larger ones (10%). Figure 4. Evolution of the slip velocity. Vs, as a function of the top plate velocity, Vt, for a PDMS melt of molecular weigt 9.6 lO in contact with a silica surface pretreated by grafting an almost dense monolayer of OTS. The two dotted lines are respectively Vj =V, and Vs= VtA/d. Clearly, slip is always present, as indicated by the fact that the measured Vj is always above the average velocity one would have inside a layer of thickness A, in the case of a linear velocity gradient and no slip (lower dotted line). At very high shear rates V, becomes comparable to Vt and the flow is almost a plug flow. The experimental relative uncertainty on Vj is larger for the low slip velocities (close to 20%) than for the larger ones (10%).
Funatsu K. and Sato M., "Measurement of slip velocity and normal stress difference of polyvinylchloride, Adv. in Rheol., 4 (Mexico 1984) 465-472. Knappe W. and E. Krumbock, "Evaluation of slip flow of PVC compounds by capillary rheometry," Adv. in Rheol., 3 (Mexico 1984) 417-424. de Smedt C., Nam S., "The processing benefits of fluoroelastomer appUcation in LLDPE," Plast. Rubber Process. Appl. 8,11 (1987). [Pg.387]

GAP-DEPENDENT APPARENT SHEAR RATE. Indirect evidence of slip, as well as a measurement of its magnitude, can be extracted from the flow curve (shear stress versus shear rate) measured at different rheometer gaps (Mooney 1931). If slip occurs, one expects the slip velocity V (a) to depend on the shear stress a, but not on the gap h. Thus, if a fluid is sheared in a plane Couette device with one plate moving and one stationary, and the gap h is varied with the shear stress a held fixed, there will be a velocity jump of magnitude Vs(ct) at the interfaces between the fluid and each of the two plates. There will also be a velocity gradient >(a) in the bulk of the fluid thus the velocity of the moving surface will be y = 2V,(a) + y (a)/i. The apparent shear rate V/h will therefore be... [Pg.32]

A plot of yapp against 1 / h will then be a straight line with slope 2Vs. This method has been used to measure the slip velocity for polyethylene melts in a sliding plate (plane Couette) rheometer by Hatzikiriakos and Dealy (1991). Analogous methods have been applied to shearing flows of melts in capillaries and in plate-and-plate rheometers (Mooney 1931 Henson and Mackay 1995 Wang and Drda 1996). [Pg.32]


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See also in sourсe #XX -- [ Pg.199 ]




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