Hole diameter

Once the bench height has been determined, the diameter of the blast hole is next for consideration. The suggested ratio between bench height and blast hole diameter (Konya and Walter, 1990) is given by Equation (4.1)  

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However, is dependent on the ratio of hole diameter to pipe diameter, pipe wall thickness to hole diameter ratio, and pipe velocity to hole velocity ratio. As long as all these are small, the coefficient 0.62 is generally adequate. 

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 ) . 

Fair s empirical correlation for sieve and bubble-cap trays shown in Fig. 14-26 is similar. Note that Fig. 14-26 incorporates a velocity dependence (velocity) above 90 percent of flood for high-density systems. The correlation implicitly considers the tray design factors such as the open area, tray spacing, and hole diameter through the impact of these factors on percent of flood. 

For effluent streams consisting of only liquid and vapor, hole diameters ranging from Vh to V2. in are recommended. Larger hole diameters (up to 2 in) may be required if the blowdown stream contains solids (polymers and/or catalyst). However, the violently collapsing vapor bubbles create a water hammer effect which increases in severity with hole size. 

It is essential to ensure that the following criteria are met otherwise errors will result. First, the mouth of the hole inside the duct must be smooth and flush with the duct inner surface. No burrs or other irregularities must be on the surface in the vicinity of the hole. Second, the hole must be perpendicular to the tube axis. The size of the hole has an effect on the measured pressure as well. A general rule is, the smaller the hole the better. Very small holes do, however, slow down the response of the instrument. Usually the hole diameter is a few millimeters. Note also that the smaller the hole, the greater the risk of blockage. Further information on the effect of the hole size can be found, e.g., in Ower and Pankhurst. 

Holes spaced closer than twice the hole diameter lead to unstable operation. The recommended spacing is 2.5 do to 5 do with 3.8 do being preferable [42]. Holes are usually placed on 60° equilateral triangular pitch with the liquid flowing norrrially to the rows. Holes should not be greater than 2.5-3 in. apart for effective tray action. 

Co is a function of the velocity of approach, hole diameter/tray-thickness ratio, Reynold s number through the... 

The equivalent hole diameter for use in the equation for Z when considering the two types of valve trays studied here is given by ... 

For the valve tray equivalent hole diameter, see illustration. 

Dhe = equivalent hole diameter, in.. Equation 8-280 = valve diameter, in. 

As tray spacing increases, entrainment reduces in quantity, but does increase with the sieve tray hole diameter [183, 184], but generally increases with reduction in hole... 

No correction for hole diameter < M in. Correction factors for larger diameters not known. 

From the selected design hole velocity and the total rapor rate corresponding, the total number of holes can be determined for a given assumed hole diameter. 

With a hole/active area ratio = 8.66/65.59 = 0.132 With a tray thickness/hole diameter ratio = 0.078/(3/16)... 

Area, Hole Diameter, Hole Spacing Weir Height and Downcomer Area, Pet. Ref. V. 34, p. 114 (1935). 102. 

Equation 9-1 can be used to correlate the number of holes to the liquid head for a specific hole diameter, d ... 

TEMA Standard Tube Hole Diameters and Tolerences (All Dimensions in In.)... 

Nominal Tube O.D. Nominal Tube Hole Diameter and Under Tolerance Over Tolerance 96% of tube holes must meet value in colmnn (c). Remainder may not exceed value in colmnn (d). ... 

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