Static liquid hold

The static liquid hold-up can be determined from the difference with the weight of the TBR after a minimum time of draining with the same TBR dry packing. 

Figure 5.2-24. Experimental static liquid hold-up as a function of the Eotvos number (after Wammes et al. [34]).

Van Swaaij [52] and Charpentier et al. [53] proposed a relationship between the static liquid hold-up, I3stat, and the dimensionless Eotvos number, Eo. At high Eotvos numbers the static hold-up is inversely proportional to Eo, whereas at low Eotvos numbers, the static holdup reaches a maximum value. 

Wammes et al. [34], by employing three different liquids (water - ethanol and 40 % ethyleneglycol aqueous solution) with 3 mm glass spheres, obtained experimentally determined static hold-up data. Figure 5.2-24 shows the values of the static holdup as a function of the Eotvos number together with data of other authors. Wammes et al. [34] concluded that the static liquid hold-up is not affected by the total reactor pressure. 

Ortiz-Arroyo, A. Larachi, F. Iliuta, I. Method for inferring contact angle and for correlating static liquid hold-up in packed beds. Chem. Eng. Sci. 2003, 58 (13), 2835-2855. 

Here, the static liquid hold-up reaches the value of the adhesion hold-up hn- The adhesion hold-up hn is dependent on the following number [44], see Fig. 4-2,... 

Total liquid hold-up in packed bed, h[ = static hold-up, hg, plus operating hold-up, ho [64, 66]. 

A well-substantiated correlation for air-water systems taken from the trickle bed literature (Morsi and Charpentier, 1981) was used for the volumetric mass transfer coefficients in the / , and (Rewap)i terms in the model. The hi term was taken from a correlation of Kirillov et al. (1983), while the liquid hold-up term a, in Eqs. (70), (71), (74), (77), and (79) were estimated from a hold-up model of Specchia and Baldi (1977). All of these correlations require the pressure drop per unit bed length. The correlation of Rao and Drinkenburg (1985) was employed for this purpose. Liquid static hold-up was assumed invariate and a literature value was used. Gas hold-up was obtained by difference using the bed porosity. 

The total external liquid hold-up is equal to the sum of the static-and dynamic-hold-ups. 

At the tray floor, the static liquid head tends to force liquid down through the perforations. The vapor pressure drop counteracts the downward force and acts to keep liquid on the tray. Weeping takes place when the liquid head on the tray exceeds the pressure drop that is holding the liquid on the tray. 

Pulsed columns, depicted in Fig. 6.3-2, are frequently used in solvent extraction. The design of pulsed packed colunms is identical with the design of static packed columns. Just the two-phase liquid hold-up is periodically vertically moved with the frequency /. Typically, the pulsation height is about 0.8-1.2 cm. Very common is a pulsation intensity of a / 1-2.5 cm/s. The pulsation effects a decrease of droplet size and, in turn, an increase of interfacial mass transfer rates. 

As a sponge to hold a static liquid phase which is the active adsorbent. 

This means that the total liquid hold-up hL can be equated with the dynamic liquid holdup hj). According to Mersmann and Deixler [44], the static hquid hold-up hL,st prevails in the case of very low, dimensionless liquid load Bl, acc. to Eq. (4-16) ... 

Static holdup depends upon the balance between surface-tension forces tending to hold hquiciin the bed and gravity or other forces that tend to displace the liquid out of the bed. Estimates of static holdup (for gravity drainage) may be made from the following relationship of Shulman et al. [Am. Jn.st. Chem. Eng. J., 1, 259 (1955)] ... 

The static hold-up is independent of liquid and gas rates, since it represents the liquid held in the packing after a period of drainage time, usually until constant weight of material is received. This requires approximately 1 hour for a 10-in. dia. x 36-in. packed height tower. Table 9-34 adequately summarizes the data. 

In order to use the data in systems handling liquids other than water correction equations and charts are used [66]. The charts are more convenient to use and are presented in Figures 9-46 A, B, C, D. First, determine the total or static hold-ups for water at 20°C second, determine separately the correction for viscosity, density, and surface tension third, multiply the water hold-up by each... 

Static hold-up for water, ft- /ft packing volume Water hold-up, ft liquid/ft tower volume Enthalpy of air saturated at bulk water temperature, Btu/lb dry air... 

Van der Waals, whose theory has been further developed by Hulshoff and by Bakker, went one step further than Gibbs by assuming that there exists a perfectly continuous transition from one medium to the other at the boundary. This assumption limits him to the consideration of one particular case that of a liquid in contact with its own saturated vapour, and mathematical treatment becomes possible by the further assumption that the Van der Waals equation (see Chapter II.) holds good throughout the system. The conditions of equilibrium thus become dynamical, as opposed to the statical equilibrium of Laplace s theory. Van der Waals arrives at the following principal results (i) that a surface tension exists at the boundary liquid-saturated vapour and that it is of the same order of magnitude as that found by Laplace s theory (2) that the surface tension... 

Measurements of static light or neutron scattering and of the turbidity of liquid mixtures provide information on the osmotic compressibility x and the correlation length of the critical fluctuations and, thus, on the exponents y and v. Owing to the exponent equality y = v(2 — ti) a 2v, data about y and v are essentially equivalent. In the classical case, y = 2v holds exactly. Dynamic light scattering yields the time correlation function of the concentration fluctuations which decays as exp(—Dk t), where k is the wave vector and D is the diffusion coefficient. Kawasaki s theory [103] then allows us to extract the correlation length, and hence the exponent v. 

Weeping Weeping is liquid descending through the tray perforations, snort-circuiting the contact zone, which lowers tray efficiency. At the tray floor, liquid static head that acts to push liquid down the perforations is counteracted by the gas pressure drop that acts to hold the liquid on the tray. When the static head overcomes the gas pressure drop, weeping occurs. 

As shown in Fig. 8.6, several typical flow patterns can be found in the monolith channels, depending on gas-liquid ratio, flow rates, viscosity, surface tension, and channel diameter. All of these flow patterns show a very low static hold-up, but only two are regular and allow stable operation the so-called Taylor-flow and the film-flow regime. 

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