F factor

The F factor is used in the expression U = F/(Pv) to obtain the allowable superficial vapor velocity based on free column cross-sectional area (total column area minus the downcomer area). For foaming systems, the F factor should be multiplied by 0.75. 

Clear liquid velocity (ft/sec) through the downcomer is then found by multiplying DL by 0.00223. The correlation is not valid if Pl - Pv is less than 30 Ib/ft (very high pressure systems). For foaming systems, DL should be multiplied by 0.7. Frank recommends segmental downcomers of at least 5% of total column cross-sectional area, regardless of the area obtained by this correlation. 

For final design, complete tray hydraulic calculations are required. 

For even faster estimates, the following rough F factor guidelines have been proposed  

Fractionating column total cross section vapor velocity 1.0-1.5 

Fractionating coiumn totai cross section vapor veiocity 1.0-1.5 Sieve tray hoie velocity to avoid weeping 12 

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The first term (AQ) is the pressure drop due to laminar flow, and the FQ term is the pressure drop due to turbulent flow. The A and F factors can be determined by well testing, or from the fluid and reservoir properties, if known. 

He observed an f-factor of 3 and argued for the formation of the di-protonated acid. He interpreted the high electrical conductivity of these media in support of this. 

The situation has been examined more recently and an f-factor of about 4 has been observed, consistent with the formation of the nitro-nium ion. The actual value was 3-82, slightly lower than expected because the water formed is not fully protonated. 

Frequently, the difference ia exchanger type does not influence the desired topology to any significant extent. For iadustrial problems, however, it is necessary to consider iadividual heat-exchanger shells rather than just the match that is called the heat exchanger. If a high level of heat recovery is desired, the effect of the F factor can be important. This problem has been solved but is beyond the scope of this article. 

R = factor for electrical relaxation D = dielectric constant of medium F = factor for size of spheres and = zeta potential. 

F, Factor, ratio of temperature difference across tube-side film to overall mean temperature difference Dimensionless Dimensionless... 

For the design condition, F-factor is 2.08 n l/sfkg/m ), or about 76 percent of flood. The proposed column is entirely adequate for the service required. 

The data show a midrange dry efficiency of 0.7 (70 percent). They indicate a flood F-factor value of about 3.0. Thus, the approach to flood is 2.6/3.0 = 0.87 (87 percent). The data were taken at total reflux, and thus F c = (0.481/841)0.5 = 0.024 (densities taken from Example 9). From Fig. 14-26, = 0.19, and from... 

Example 11 Pressure Drop Sieve Plate For the conditions of Example 10, estimate the pressure drop for flow across one plate. The thickness of the plate metal is 2 mm and the hole diameter is 4.8 mm. The superficial F-factor is 2.08 m/s(kg/m ) . 

The F-factors of 5.0 and 8.0 are cousei vative in the opinion of the researcher who performed the experiments (private communication from E. I. dll Pout de Nemours Co., Inc., to the DIERS Project). 

The F factor correlation from Frank is shown in Figure... 

Figure 1. F Factor as a function of column pressure drop and tray spacing.

F = Factor for fractionation allowable velocity P = Column pressure, psia T = Tray spacing, in. 

F Factor. The use of the F factor for fractionating column diameter quick estimation is shown in Reference 3. The developed equation for the F factor is ... 

P = Pressure, psia for fractionator F factor correlation or psig for vessel thickness calculation... 

Vk = Capacity of the known plant F = Factor, usually between 0.4 and 0.9, depending on the type of plant... 

The assumptions hold so well that the F factor charts are standardized by TEMA for shell and tube heat exchanger design. 

Figure 2-3. Moody or regular Fanning friction factors for any kind and size of pipe. Note the friction factor read from this chart is four times the value of the f factor read from Perry s Handbook, 6th Ed. [5]. Reprinted by permission, Pipe Friction Manual, 1954 by The Hydraulic Institute. Also see Engineering DataBook, 1st Ed., The Hydraulic Institute, 1979 [2]. Data from L. F, Moody, Friction Factors for Pipe Flow by ASME [1].

To take credit for reduced heat input, the insulation shall resist dislodg-ment by a fire-hose stream, shall be noncombustible, and shall not decompose at temperatures up to 1000 F, If the insulation does not meet these criteria, the F factor for a bare vessel shall be used. 

The insulation credit is arbitrarily limited to the F factor shown for 12 inches of insulation, even though greater thicknesses may be used. More credit, if taken, would result in a relieving device that would be impracti-cally small but that might be used if warranted by design considerations. Twice the F factor for an equivalent thickness of insulation. 

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