Wetted surface area

D. Absorption and and distillation, counter-current, gas and liquid individual coefficients and wetted surface area, Ouda et al. correlation for random pacldugs... 

Another type of air washer is the capillary air washer see Fig. 9.16. It consists of many thousands of small glass or plastic filaments (cells) providing a large, wetted surface area. These are placed to allow a parallel path of air through them. The surface of each of these strands is covered with the water that is discharged from sprays. 

Tlie area, A, in tliis equation is tlie entire surface area of the vessel, not the wetted surface area wliich maybe used in related equations. However, tlie error introduced by tliis difference in tlie calculation for a full tank is small. 

Total Rate of Emergency Venting Required for Fire Ebcposure Vs. Wetted Surface Area (wetted area vs. ft. of free air/hr, 14.7 psia, 60°F)... 

Note Above 2800 square feel of weiied surface area, the total heat absorption is considered to remain constant for nonrefrigerated tanks below I pound per squa. e inch gage. For nonrefrigerated tanks above I pound per square inch gage and for all refrigerated tanks, the total heat absorption continues to increase with wetted surface area. This is the reason why the curve splits above 2800 square feel. 

A = wetted surface area, in square feet (see Table 3, Footnote a). 

A, = vent area, sq meters or sq ft A = total wetted surface area, sq ft AIT = auto-ignition temperature... 

The above discussion is applicable to layers unpeirturbed by the presence of a vapor phase, such as in a sandwich layer tank. In practice, most separations are performed in large volume chanbers in the presence of a vapor phase. It is almost impossible to fully saturate such chanbers so that a temporal and spatial vapor equilibrium is unlikely to. exist. Two opposing phenomena can be expected to influence the rate of solvent migration. Vaporization of solvent from the wetted layer might reasonably be expected to depend on the wetted surface area of the plate and the vapor pressure of the solvent in the tank. The loss of solvent from the layer will result in a reduction of the mobile phase... 

Increasing the water-wet surface area of a petroleum reservoir is one mechanism by which alkaline floods recover incremental oil(19). Under basic pH conditions, organic acids in acidic crudes produce natural surfactants which can alter the wettability of pore surfaces. Recovery of incremental oil by alkaline flooding is dependent on the pH and salinity of the brine (20), the acidity of the crude and the wettability of the porous medium(1,19,21,22). Thus, alkaline flooding is an oil and reservoir specific recovery process which can not be used in all reservoirs. The usefulness of alkaline flooding is also limited by the large volumes of caustic required to satisfy rock reactions(23). 

The dissolution rate of a given solid is usually strictly proportional to the wetted surface area A of the dissolving solid, shown in Fig. 13 thus,... 

The diffusion layer model satisfactorily accounts for the dissolution rates of most pharmaceutical solids. Equation (43) has even been used to predict the dissolution rates of drugs in powder form by assuming approximate values of D (e.g., 10 5 cm2/sec), and h (e.g., 50 pm) and by deriving a mean value of A from the mean particle size of the powder [107,108]. However, as the particles dissolve, the wetted surface area, A, decreases in proportion to the 2/3 power of the volume of the powder. With this assumption, integration of Eq. (38) leads to the following relation, known as the Hixon-Crowell [109] cube root law ... 

The intrinsic dissolution rates of pharmaceutical solids may be calculated from the dissolution rate and wetted surface area using Eq. (36) or (37). For powdered solids, two common methods are available the powder intrinsic dissolution rate method, and the disc intrinsic dissolution rate method. In the former method, the initial dissolution rate of one gram of powder is determined by a batch-type procedure as illustrated in Fig. 13A. The initial wetted surface area of one gram of powder is assumed to equal the specific surface area determined by an established dry procedure, such as monolayer gas adsorption by the Brunauer, Emmett, and Teller (BET) procedure [110]. 

In the disc method, the powder is compressed by a punch in a die to produce a compacted disc, or tablet. The disc, with one face exposed, is then rotated at a constant speed without wobble in the dissolution medium. For this purpose the disc may be placed in a holder, such as the Wood et al. [Ill] apparatus, or may be left in the die [112]. The dissolution rate, dmldt, is determined as in a batch method, while the wetted surface area is simply the area of the disc exposed to the dissolution medium. The powder x-ray diffraction patterns of the solid after compaction and of the residual solid after dissolution should be compared with that of the original powder to test for possible phase changes during compaction or dissolution. Such phase changes would include polymorphism, solvate formation, or crystallization of an amorphous solid [113],... 

Wetted surface area, A, which consequently is normalized in measurements of intrinsic dissolution rate, J (Eq. 35). 

The wetted surface area of the 2 m3 reactor during two-phase relief has been estimated as 8.6 m2. This is the full surface area of the bottom and the sides of the reactor because, if two-phase relief occurs, this whole area will be wetted inside the reactor with liquid. The heat input rate from the fire is estimated as 252 kW l For a closed reactor containing 793 kg of material, and using the average, specific heat capacity of 2.25 kJ/kg K, the effective rate of temperature rise due to the fire is given by ... 

Wetted surface area—the number of square feet of packing surface area available for vapor-liquid contacting, per cubic foot of tower volume. 

Structured packing has about 50 percent more open area than Raschig rings and two or three times their wetted surface area. Hence, structured packing has largely replaced packing in the form of rings, in many packed towers. 

Since liquid does not completely wet the packing and since film thickness varies with radial position, classical film-flow theory does not explain liquid flow behavior, nor does it predict liquid holdup (30). Electrical resistance measurements have been used for liquid holdup, assuming liquid flows as rivulets in the radial direction with little or no axial and transverse movement. These data can then be empirically fit to film-flow, pore-flow, or droplet-flow models (14,19). The real flow behavior is likely a complex combination of these different flow models, that is, a function of the packing used, the operating parameters, and fluid properties. Incorporating calculations for wetted surface area with the film-flow model allows prediction of liquid holdup within 20% of experimental values (18). 

Step 1 Determine the total wetted surface area. 

The following formulas are used to determine the wetted surface area of a vessel (potential surface in contact with the stored liquid). They use the logic as stated in API RP 521, Fourth Edition, table 4 Effects of Fire on the Wetted Surfaces of a Vessel. ... 

Awet = Total wetted surface area in square feet (see calculations in Step 1)... 

Wetted surface area of the packing per unit volume, ft /ft3, given by Eq, (9,16)... 

Determine the amount of water removed under peak drying conditions. Multiply the wetted surface area by the peak drying rate. Thus, (206 ft2)[2.0 lb/(h)(ft2)] = 412 lb/h (187 kg/h). 

Here, is the viscosity of fluid, g the gravitational constant, and a , the wetted surface area. According to this model, an expression for the RTD for an impulse input is given by... 

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