Wetting Rate

A nomograph for the calculation of wetting rates is given in Volume 2, Chapter 4. 

Wetting rates are frequently expressed in terms of mass or volume flow-rate per unit column cross-sectional area. 

If the design liquor rate is too low, the diameter of the column should be reduced. For some processes liquid can be recycled to increase the flow over the packing. 

A substantial factor of safety should be applied to the calculated bed height for process where the wetting rate is likely to be low. 

10 to 0.14 X 10 s Vm ) for structured packing. Norman (1961) recommends that the liquid rate in absorbers should be kept above 2.7 kg/m s. 

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Minimum Wetting Rate The minimum liquid rate required for complete wetting of a vertical surface is about 0.03 to 0.3 kg/m s for water at room temperature. The minimum rate depends on the geom-etiy and nature of the vertical surface, liquid surface tension, and mass transfer between surrounding gas and the liquid. See Ponter, et al. Int. J. Heat Mass Tran.fer 10, 349-359 [1967] Trans. Inst. Chem. Eng. [London], 45, 345—352 [1967]), Stainthorp and Allen Trans. Inst. Chem. Eng. [London], 43, 85-91 [1967]) and Watanabe, et al. ]. Chem. Eng. [Japan], 8[1], 75 [1975]). 

To feed enough liquid into the tower to effectively place a wet film of liquid over all the packing, a minimum wetting rate (MWR) has been evaluated for guidance in operation and design. Morris and Jackson [52] recommended the MWR shown in Table 9-24. 

MWR = value of minimum wetting rate from Table 9-24... 

The minimum wetting rate is a function of the packing material surface (Table 9-25) and the physical properties of the liquid involved, particularly the viscosity and the... 

Packing Wetting Rates Related to Pacldng Material Surface... 

Kister [90] has evaluated Schmidt s [92] somewhat complicated equation for minimum wetting rate and proposes ... 

Note that when packing is changed from one material of construction to another, it is important to recognize the effect on minimum wetting rate for the new condition. 

Vacuum service requires recognition of minimum liquid flow refer to section on minimum wetting rate. Pressure drops are designed to be low, but normally not lower than 0.10 in. water/ft. 

Lmin = Minimum liquid wetting rate in packed tower, ft /(hr) (ft cross-section)... 

MWRg = Minimum wetting rate, gpm/ft, (Eq. 9-14) MWRj = Minimum wetting rate, gpm/ft, constant,... 

Temperature gas inlet, °C maximum catalyst, °C Pressure, psig Product gas (wet) rate, scfh H2, vol %... 

Ethylene oxide adducts of alkanephosphonic acids exhibit a better solubility in water and partly an interesting depression of the surface tension in aqueous solutions (Table 9). Although foamability and wetting rate lie in a medium range, they possess no emulsifying ability. 

The responses chosen all relate to important foam properties. We believed that yi, the emulsion droplet size, determines y2, the cell size in the resultant foam, and we wished to determine whether this is true over this range of formulations. The foam pore size ys should determine the wetting rate y7, so these responses could be correlated, and yg, the BET surface area, should be related to these as well. The density y and density uniformity ys are critical to target performance as described above, and ys, the compressive modulus, is an important measure of the mechanical properties of the foam. 

A set of nomographs are given in Volume 2, Chapter 12 for the estimation of Hg and Hl, and the wetting rate. These were taken from a proprietary publication, but are based on a set of similar nomographs given by Czermann et al. (1958), who developed the nomographs from correlations put forward by Morris and Jackson (1953) and other workers. 

If very low liquid rates have to be used, outside the range of FLV given in Figure 11.44, the packing wetting rate should be checked to make sure it is above the minimum recommended by the packing manufacturer. 

Chlorine is to be removed from a vent stream by scrubbing with a 5 per cent w/w aqueous solution of sodium hydroxide. The vent stream is essential nitrogen, with a maximum concentration of 5.5 per cent w/w chlorine. The concentration of chlorine leaving the scrubber must be less than 50 ppm by weight. The maximum flow-rate of the vent stream to the scrubber will be 4500 kg/h. Design a suitable packed column for this duty. The column will operate at 1.1 bar and ambient temperature. If necessary, the aqueous stream may be recirculated to maintain a suitable wetting rate. 

Experimental conditions and initial rates of oxidation are summarized in Table V. For comparison, initial rates of dry oxidation at the same temperature and pressure of oxygen predicted by Equation 9 are included in parentheses. The predicted dry rate, measured dry rate, and measured wet rates are compared in Figure 2. The logarithms of the initial rates of heat production during wet oxidation increase approximately linearly (correlation coefficient = 0.92) with the logarithm of the partial pressure of oxygen and lead to values of In k = 2.5 and r = 0.9, as compared with values of In k = 4.8 and r = 0.6 for dry oxidation at this temperature. 

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