Velocity, maximum allowable

Figure 14-25 or Eq. (14-92) may be used for sieve plates, valve plates, or bubble-cap plates. The value of the flooding vapor velocity must be considered as approximate, and prudent designs call for approaches to flooding of 75 to 85 percent. The value of the capacity parameter (ordinate term in Fig. 14-25) may be used to calculate the maximum allowable vapor velocity through the net area of the plate ... 

Sizing Cooling Water Piping in New Plants Maximum Allowable Flow, Velocity and Pressure Drop... 

The maximum allowable mass velocity for the total column cross section is calculated as follows ... 

C = Souders-Brown maximum allowable mass velocity factor... 

SsTD = Standard maximum allowable velocity for tower cross section, ft/sec... 

W = Souders-Brown maximum allowable mass velocity, lbs/(ft cross section) (hr)... 

The diameter of a tower is established by the volume of vapors which must be handled and by the maximum allowable vapor velocity which can be tolerated without encountering excessive entrainment of liquid from one plate to the plate above. Entrainment can occur by splashing and/or suspension of small droplets in the vapor as a mist. It tends to defeat the purpose of fractionation even a small amount may be serious when rigid specifications on color or impurities must be met. 

The maximum allowable superficial velocity of air in the stripper can be estimated using the following expression (based on the data provided by Peters and Timmerhaus (1991) for 0.41-m tray spacing) ... 

Z = gas compressibility factor R = gas/liquid ratio, ft /bbl T = operating temperature, °R P = pressure, psia Qi = liquid flow rate, bbl/day V = maximum allowable velocity, ft/sec... 

The usual practice in selecting a particular mesh for a given service is to determine the maximum allowable velocity and from this select a vessel diameter. In the case of existing vessels where mesh is to be installed, the reverse procedure is used, i.e., determine the velocity con-... 

A rough approximation of operating mesh pressure drop is 1 inch water or less. The calculated pressure drop at the maximum allowable velocity is close to 1.5 inches of water. Therefore ... 

Very low velocities U ill allow particles to drift through the mesh and be carried out with the lea dng vapor. Also, very high velocities will carry liquid to the top of the mesh, establish a flooding condition, and then reentrain the lit]uid from the surface of the mesh. For most situations very good performance can be expected for all velocities from 30% to 100% of the optimum allowable design velocity. The minimum allowable safe design velocity is 10 percent of the value calculated by the equation. The flooding velocity of the mesh is usually about 120 percent to 140 percent of the maximum allowable velocity. 

Generally the maximum allowable velocities are lower under conditions of pressure, and higher under conditions of vacuum. The limits and ranges of each area being determined by the relative operating densities of the vapor and liquid, the nature of the entrainment, and the degree of separation required. 

WTen the mesh is installed with the pad vertical or inclined, die maximum allowable velocity is generally used at 0.67 umes the allowable value for the horizontal position. 

V (separator) = Separator vapor velocity evaluated for the gas or vapor at flotving conditions, ft/sec V = Vapor velocity entering unit, lbs, per minute per square foot of inlet pipe cross section Va = Maximum allowable vapor velocity across inlet face of mesh calculated by relation, ft/sec Van Actual operating superficial gas velocity, ft/sec or ft/min, for tvire mesh pad Vu = Design vapor velocity (or selected design value), ft/sec... 

V ,ax = Calculated maximum allowable superficial gas velocity, ft/sec, or ft/min tvire mesh pad Vs = Superficial gas velocity, ft/sec Vsa = Separator vapor velocity evaluated for air-water system, ft/sec... 

The Souders-Brown [67] empirically correlated maximum allowable mass velocity is represented in Figure 8-82 for C Factor determination, and in Figure 8-83 for solution of the relation ... 

Maximum Allowable Mass Velocity, lb8./(sq.ft,Cross Section)(Hour)... 

Turndown ratio is the ratio of the maximum allowable vapor rale at or near flooding conditions (rates) to the minimum vapor rate when weeping or liquid leakage becomes significant it may be termed the minimum allowable vapor velocity [193, 199, 200]. 

Vapor load corrected for density, ft/sec Maximum allowable vapor load per tray, ft /sec Superficial vapor velocity in tower, ft/sec (based on tower cross ection)... 

Flow rate = 136 gpm Design for (136) (1.5) = 204 gpm Maximum allowable velocity 6 ft/sec Referring to Cameron hydraulic tables ... 

These devices are generally designed to meet specific pressure-drop limitations. For ordinary installations operating at approximately atmospheric pressure, fan limitations dictate a maximum allowable pressure drop corresponding to a cyclone inlet velocity in the range of 20 to 70 feet per second. Consequently, cyclones are usually designed for an inlet velocity of 50 feet per second. 

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