Hole area, selection

From a consideration of contacting requirements, a tower 9.5 ft in diameter is selected. Other pertinent details are 24-in. tray spacing, 1-in. weir height, /e-in. dia. holes, 10% hole area (referred to active area) and 8.3 ft downcomer area. 

From Figure 8-144 or by calculation determine the plate area required for the holes on the pitch selected. Several selections may be tried to be used with the tray layout. These should be checked to agree with the assumed per cent hole area of Step 3. 

Select as quite common Me-in. dia. holes, with hole area/tower area = 0.10, 14 U S Std. gauge stainless steel tray material, which is 0.078 in. thick, 2-in. weir height, and 24-in. tray spacing. 

The hole pitch (distance between the hole centres) l p should not be less than 2.0 hole diameters, and the normal range will be 2.5 to 4.0 diameters. Within this range the pitch can be selected to give the number of active holes required for the total hole area specified. 

Reference A3 (Figure 11.28) details the recommended plate configuration for liquid flowrate versus column internal diameter. A reverse flow-type sieve plate is suggested as shown in Figure 9.3. The pitch of the sieve-tray holes is selected so that the total hole area is reduced to 0.07 times the total column area. The other design criteria employed to provide the provisional plate specification are detailed in Table G,3. 

Select a tray deck thickness VLVTH. Standards are 0.074, 0.104, 0.134, and 0.25 in. The hole area of a current-day valve-type tray is calculated from ... 

In an irradiated semiconductor, electron-hole pairs are generated according to the band gap excitation. Therefore, when the semiconductor is area-selectively irradiated, electron-hole pairs are generated exclusively in the irradiated part. Thus generated electrons and holes undergo reactions at the electrode/ electrolyte interface and such reactions are observed as area-selective reactions. 

The following guidelines apply to fractional hole area and hole pitch selection ... 

When setting tray pitch, it is preferable to select a standard punching pattern, used by tray fabricators, and to adjust the hole pitch accordingly. A nonstandard pattern increases the cost of trays. Following this practice rarely alters the desired fractional hole area substantially. 

To select the hole area. I ll first calculate the weight of liquid on the tray. This consists of two parts the weir height and the crest height. 

To summarize. I ll select a hole area for the tray, so that the velocity of vapor flowing through the holes will be big enough to keep the tray from leaking. Of course, if the tray decks are badly out of level, the above calculations are meaningless. So don t forget to inspect your tray installation for tray deck levelness (see my book. Process Equipment Malfunctions, McGraw-Hill, 2011). 

CVD processing can be used to provide selective deposition on certain areas of a surface. Selective tungsten CVD is used to fill vias or holes selectively through siUcon oxide layers in siUcon-device technology. In this case, the siUcon from the substrate catalyzes the reduction of tungsten hexafluoride, whereas the siUcon oxide does not. Selective CVD deposition can also be accompHshed using lasers or focused electron beams for local heating. 

Another interesting applications area for fullerenes is based on materials that can be fabricated using fullerene-doped polymers. Polyvinylcarbazole (PVK) and other selected polymers, such as poly(paraphcnylene-vinylene) (PPV) and phenylmethylpolysilane (PMPS), doped with a mixture of Cgo and C70 have been reported to exhibit exceptionally good photoconductive properties [206, 207, 208] which may lead to the development of future polymeric photoconductive materials. Small concentrations of fullerenes (e.g., by weight) lead to charge transfer of the photo-excited electrons in the polymer to the fullerenes, thereby promoting the conduction of mobile holes in the polymer [209]. Fullerene-doped polymers also have significant potential for use in applications, such as photo-diodes, photo-voltaic devices and as photo-refractive materials. 

Actually not all of the tray needs to be drilled. However, the location of dead or unperforated areas must be carefully selected, preferable next to weirs. A special punching (or drilling) arrangement for the holes can run the cost of the trays quite high. It will probably be preferable to check effect of punching holes in entire area A B C D of Figure 8-145. 

Rotary Speed. Diamond bits can usually be rotated at up to 150 rpm without any problem when hole conditions and drill string design permit. Rotary speeds of 200 and 300 rpm can be used with stabilized drill strings in selected areas. Diamond bits have also operated very successfully with downhole motors at 600 to 900 rpm. The actual rotary speed limits are usually imposed by safety. 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Investigations of the kinetics of hole transfer in DNA by means of pulse radiolysis of synthetic ODNs have provided details about the hole transfer process, especially over 1 /is, including the multi-step hole transfer process. Based on the investigation of the kinetics of hole transfer in DNA, development of the DNA nanoelectronic devices is now expected. An active application of the hole transfer process is also desirable from a therapeutical point of view, since hole transfer may play a role in improvement of quantum yield and selectivity of DNA scission during photodynamic therapy. The kinetics of the hole transfer process is now being revealed, although there is still much research to be performed in this area. The kinetics of adenine hopping is another area of interest that should be explored in the future. 

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