Velocity diameter

The charging current is therefore roughly proportional to the square of (ucO, the velocity-diameter product. An important outcome is that the velocity-diameter product can be used to characterize charging current in pipe flow and as a basis for setting flow limits when filling tanks (5-4). 

As discussed in 5-4.2 and 5-4.3, three different maximum velocity-diameter vd) products can be found in current recommended practices. Values... 

An important practical question is, what is the representative pipe diameter in loading circuits comprising different sizes of pipe This has a large effect on the values calculated for velocity and velocity-diameter product. As an example, static ignition of ester mist in a rail car (5-1.3.1) involved 1450 gpm through a 6-in. pipe (v = 5 m/s and vd = 0.76 mVs) followed by a short 4-in. dip pipe assembly (y = 11 m/s and vd = 1.15 mVs). Were nonconductive liquid flow rate restrictions applied to the semiconductive ester (time constant —0.01 s) involved in this fire, the flow rate based on the 4-in. pipe would be unacceptably large based either on a 7 m/s maximum velocity or a 0.80 mVs maximum vd product. However, based on the 6-in. pipe upstream the flow velocity is less than 7 m/s and also meets API s vd < 0.80 mVs criterion. 

Since velocity varies with the inverse square of pipe diameter d, an important consideration is the selection of pipe diameter. For any given velocity-diameter product, larger pipe diameters allow larger flow rates. Since occasional static ignitions in road tankers may occur at nr/ = 0.38 mVs, smaller values might be considered for nonconductive liquid transfer depending on risk tolerance. 

Note 1. When loading volatile products such as gasoline, whose vapor concentration can be shown to rapidly exceed the upper flammable limit during tank filling, the velocity-diameter product may be increased to 0.50 mVs- This is consistent with API RP2003 [3]. Similarly, shorter wait periods of 1-2 min can be used. 

In order to establish safe values for velocity-diameter product, various studies have been made to determine the minimum liquid surface potential that will result in an incendive discharge in the presence of a grounded electrode. Studies reviewed in [8] showed that for credible charging conditions, liquids must be negatively charged to yield incendive bmsh discharges. The consensus has been that to avoid incendive discharges the maximum liquid... 

Gradual velocity reduction method. This method is a variation of the constant friction approach, where a maximum velocity is used for the main and branch ducts. This procedure provides a reasonable solution and choice between the velocity, diameter, and resistance. The method is not useful to provide the same static pressure at each outlet. 

Charge Diameter - Detonation Velocity Relationship. See under Detonation Velocity -Diameter Relationship... 

O) M.A. Cook et al, jChemPhys 24, 60-7 (1956) (Velocity-diameter and wave shape measurements and the determination of reaction rates of TNT) P) M.A. Cook ... 

Taylor (1952), 139-55 (Deton vel-charge diam relationship) 7) M.A. Cook et al, "Velocity-Diameter and Wave Shape Measurements and the Determinations of Reaction Rates in Metal Nitrate-TNT Mixtures , Univ of Utah Inst for Study of Rate Processes,... 

R.T. Keyes, "Velocity-Diameter and Wave Shape Measurements in the Determination of Reaction Rates of TNT , JChemPhys 24,... 

Figure 4 Velocity-diameter curves for some commercial explosives (1. 60 per cent ammonia gelatin 2. 40 per cent ammonia gelatin 3. 60 per cent AN-SN dynamite 4. per cent AN-SN dynamite 5. fuel sensitized coarse-fine AN explosive (pi — 1.3) 6. fine grained AN permissible (pi 0.8, NG 7 per cent) 7. intermediate grained AN permissible (pi = 0.8, NG 7 per cent) 8. coarse grained AN permissible (Pl - 0.8, NG 7 per cent) 9. fine grained AN permissible (pi 0.6)...

Detonation Velocity-Diameter of charge Relationship. See Detonation Velocity Charge Diameter Relationship... 

M.A. Cook et al, JACS 79, 32(1957) (Velocity-diameter curves, velocity transients and reaction rates in PETN, RDX, EDNA Tetryl)... 

We are interested in reaction-zone length because it appears to be the major parameter controlling detonation velocity in the nonideal detonation region. It appears that explosives with thick reaction zones have a larger effect on detonation-velocity/diameter and failure diameters than explosives with thin reaction zones. 

The same mechanism, side losses that cause steady-state detonation velocity to decrease in the nonideal region, eventually become so dominant with decreasing diameter that a point is reached where steady-state detonation cannot be maintained. At this point detonation fails it either suddenly slows down to below the sound speed in the unreacted explosive or stops altogether. This point is called the failure diameter, D, it is also called the critical diameter, Dent- Failure diameter is strongly affected by confinement, particle size, initial density, and ambient temperature of the unreacted explosive. Failure diameter can be roughly correlated to the velocity-diameter constant a, as seen in Figure 21.7. 

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