Hole sizes

The hole sizes used vary from 2.5 to 12 mm 5 mm is the preferred size. Larger holes are occasionally used for fouling systems. The holes are drilled or punched. Punching is cheaper, but the minimum size of hole that can be punched will depend on the plate thickness. For carbon steel, hole sizes approximately equal to the plate thickness can be punched, but for stainless steel the minimum hole size that can be punched is about twice the plate thickness. Typical plate thicknesses used are 5 mm (3/16 in.) for carbon steel, and 3 mm (12 gauge) for stainless steel. 

When punched plates are used they should be installed with the direction of punching upward. Punching forms a slight nozzle, and reversing the plate will increase the pressure drop. 

By far the widest area of application of molecular mechanics and related methods toward the design of metal ion selective ligands is the calculation of the hole size of macrocyclic ligands. The simplest method for determining the hole size R, is to measure from crystal stmctural data the mean distance J h of the donor atom positions from their centroid, and to correct it with the covalent radius for the size 

Neither of these problems occurs with approaches based on molecular mechanics calculations. The best fit of a metal ion M to a macrocyclic ligand L is related to the minimum in the sum of all M—L bonding interaction terms [Eq. (9.2)]. 

This term vanishes by setting either k i = 0, or Tml = fo- While the first approach corresponds to a single-point calculation [347, 348], with the latter method the total strain energy mapped as a function of the metal-ligand distance can be obtained [210]. Remember here that an accurate treatment of the metal ion selectivity should 

Apart from the different approaches to calculating hole sizes of macrocydic ligands, there are also considerable differences in the force fields that have been used [104, 125, 167, 171, 347, 349, 351-356]. Unfortunately, no comparative study that systematically analyzes the various methods and force fields is available. Therefore, it is worth noting that the computation of the cavity size of 12- to 16-membered tetraaza macrocydes with two very different models and force fields led to remarkably similar results (Table 9.2). 

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Until downhole motors became available a whipstock (Fig. 3.15) which is a slightly asymmetric steel joint, was inserted in the drill string. The assembly is oriented downhole and a rathole is drilled which is then enlarged to full bore hole size. The technique is still used in wells where hole conditions e.g. high temperatures, are unsuitable for downhole motors (see below). 

There has been a continual increase in size and complexity of PCBs with a concurrent reduction in conductor and hole dimensions. Conductors can be less than 250 p.m wide some boards have conductors less than 75 pm wide. Multilayer boards greater than 2.5 mm thick having hole sizes less than 250 pm are being produced. This trend may, however, eventually cause the demise of the subtractive process. It is difficult to etch such fine lines using 35-pm copper foils, though foils as thin as 5 pm are now available. It is also difficult to electroplate holes having high aspect ratio. These factors may shift production to the semiadditive or fully additive processes. 

Vaiy the hole size and/or the spacing between holes to compensate for the pressure variation along the pipe. This method may be sensitive to flow rate and a distributor optimized for one flow rate may suffer increased maldistribution as flow rate deviates from design rate. 

Example 9 Pipe Distrihator A 3-in schedule 40 (inside diameter 7.793 cm) pipe is to be used as a distributor for a flow of 0.010 mVs of water (p = 1,000 kg/m, i= 0.001 Pa s). The pipe is 0.7 m long and is to have 10 holes of uniform diameter and spacing along the length of the pipe. The distributor pipe is submerged. Calculate the required hole size to limit maldistribution to 5 percent, and estimate the pressure drop across the distributor. 

For sieve plates, thickness is usually in the lO-to-14 U.S. standard gauge range of 3.58 to 1.98 mm, or 0.141 to 0.078 in. Hardness of metal, size of die, and hmits on hole size (for process reasons) lead to the following thickness criterion ... 

The open area for these plates ranges from 15 to 30 percent of the total cross section compared with 5 to 15 percent for sieve plates and 8 to 15 percent for bubble-cap plates. Hole sizes range from 6 to 25 mm (1/4 to 1 in), and slot widths from 6 to 12 mm (14 to V2 in). The Turbogrid and Ripple plates are proprietary devices. 

Perforations are usually 0.32 to 0.64 cm Vh to Vi in) in diameter, set 1.27 to 1.81 cm to Vi in) apart, on square or triangular pitch. There appears to be relatively httle effect of hole size on extraction rate, except that with systems of high interfacial tension smaller holes will... 

The Karr column is particularly well suited for systems which tend to emulsify since its uniform shear characteristics tend to minimize emulsion formation. It is also particularly well suited for corrosive systems (since the plates can be constructed of non-metals) or for systems containing significant solids (due to its large open area and hole size on the plates). Slurries containing up to 30 percent solids have been successfully processed in Karr columns. 

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. 

Chemical process plants do not have a large domed containment but rely on vessel integrity and offgas processing. Most nuclear plants have such containment for which the stresses may be calculated if a scenario is defined. However such calculations are uncertain regarding the time of failure, the hole size, and location. 

Computer sensitivity studies show that hole size strongly affects the fraction of fission products released from the containment. The failure location determines mitigation due to release into another building in which condensation and particulate removal occur. The quantity released depends on the time of containment fails relative to reactor vessel failure. If containment integrity is maintained for several hours after core melt, then natural and engineered mechanisms (e.g., deposition, condensation, and filtration) can significantly reduce the quantity and radioactivity of the aerosols released to the atmosphere. 

Table 2.1. Relationship between crown hole sizes and cation diameters...

Crown Ether (hole size, A) Favored Cation (ionic diameter, A) ... 

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. 

The hole size used is larger than that necessary to quench a flame in a stagnant flammable gas mixture, i.e., larger than the quenching diameter. Howard recommends that the velocity necessary to prevent flashback be calculated by the following equation ... 

Table 4.4 Comparison of ionic diameters and crown ether hole sizes ...

Cation Ionic diam/pm Cation Ionic diam/pm Polyether ring Hole size /pm... 

Most of the literature has presented data for trays with holes of 1 -in. through M-in. diameter. The work of Hunt et al. [33] includes l in. holes. Some commercial units have used % and 1-in. holes, although these sizes should be used with caution when adequate data are not available. The recommended hole size for the average clean service is f(i-in. based on present published data. Holes of l in. 

Figure 8-137. Flooding capacity, sieve trays weir height is less than 15% of tray spacing low- to non-foaming system hole area at least 10% hole sizes Ms-in. to M-in. dia. surface tension = 20 dynes/cm. Used by permission, Fair, J. R., Petro/Chem. Engineer, Sept (1961), p. 46, reproduced courtesy of Petroleum Engineer International, Dallas, Texas.

Determine the percent hole area in the active tray portion for pressure drop calculation. Note that hole size does not have to be set at this point (Figure 8-143.)... 

Number of holes required Hole size selected = Me-in. 

Hole Size, Spacing, Percent Open Area... 

Hole size is as important in perforated plates without downcomers as far the sieve tray. Published data limits a full analysis of the relationships however, the smaller holes, Ys-in., Me-in., 4-in. appear to give slightly higher efficiencies for the same tray spacing [47]. Unfortunately the data [69] for the larger %-in. holes was not evaluated for efficiencies. Experience has indicated efficiencies equal to or only slightly, 10-15%, less for M-in. holes w hen compared to Me-in. holes for some systems. Holes as small as Mfrin., %2-in. and Me-in. were considered unsatisfactory for high surface tension materials such as water [47]. 

Myers found only a slight decrease in efficiency with an increase in hole size. Industrial experience indicates that large holes of 14-in. and %-in. can be designed to operate as efficiently as a small hole, say Xe-in. 

Fastest drilling rate in dry, hard formations. Limited by water influx and hole size. 

Drill collar programs are the same as [or the next reduced hole size. 

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