Gas stick

The impellers of such fans are suitably coated or protected against corrosion. Problems such as high vibrations when wet ash or dust carried with the gas sticks to the impellers can occur. In such cases, in situ cleaning, washing (by provision of cleaning window, water wash connection, etc.) and balancing should be possible. 

Here, if Z is expressed in moles of collisions per square centimeter per second, r is in moles per square centimeter. We assume the condensation coefficient to be unity, that is, that all molecules that hit the surface stick to it. At very low Q values, F as given by Eq. XVII-3 is of the order expected just on the basis that the gas phase continues uniformly up to the surface so that the net surface concentration (e.g., F2 in Eq. XI-24) is essentially zero. This is the situation... 

The rate of physical adsorption may be determined by the gas kinetic surface collision frequency as modified by the variation of sticking probability with surface coverage—as in the kinetic derivation of the Langmuir equation (Section XVII-3A)—and should then be very large unless the gas pressure is small. Alternatively, the rate may be governed by boundary layer diffusion, a slower process in general. Such aspects are mentioned in Ref. 146. 

Mention was made in Section XVIII-2E of programmed desorption this technique gives specific information about both the adsorption and the desorption of specific molecular states, at least when applied to single-crystal surfaces. The kinetic theory involved is essentially that used in Section XVI-3A. It will be recalled that the adsorption rate was there taken to be simply the rate at which molecules from the gas phase would strike a site area times the fraction of unoccupied sites. If the adsorption is activated, the fraction of molecules hitting and sticking that can proceed to a chemisorbed state is given by exp(-E /RT). The adsorption rate constant of Eq. XVII-13 becomes... 

Most fiindamental surface science investigations employ single-crystal samples cut along a low-index plane. The single-crystal surface is prepared to be nearly atomically flat. The surface may also be modified in vacuum. For example, it may be exposed to a gas that adsorbs (sticks) to the surface, or a film can be grown onto a sample by evaporation of material. In addition to single-crystal surfaces, many researchers have investigated vicinal, i.e. stepped, surfaces as well as the surfaces of polycrystalline and disordered materials. 

Wlien a surface is exposed to a gas, the molecules can adsorb, or stick, to the surface. Adsorption is an extremely important process, as it is the first step in any surface chemical reaction. Some of die aspects of adsorption that surface science is concerned with include the mechanisms and kinetics of adsorption, the atomic bonding sites of adsorbates and the chemical reactions that occur with adsorbed molecules. 

L exposure would produce 1 ML of adsorbates if the sticking coefficient were unity. Note that a quantitative calculation of the exposure per surface atom depends on the molecular weight of the gas molecules and on the actual density of surface atoms, but the approximations inlierent in the definition of tire Langmuir are often inconsequential. 

The first two of these we can readily approach with the knowledge gained from the studies of trappmg and sticking of rare-gas atoms, but the long timescales involved in the third process may perhaps more usefiilly be addressed by kinetics and transition state theory [35]. 

Jackson B 1994 Quantum and semiclassical calculations of gas surface energy transfer and sticking Comput. Rhys. Commun. 80 119... 

Phenylacetylene. Support a 5-litre glass Dewar flask in a wooden case. Equip the flask with a lid of clear Perspex, provided with suitable apertures for a mechanical stirrer, introducing solids (e.g., sodium) or hquids, a calibrated dip stick for measuring the volume of liquid in the Dewar vessel, a gas mlet tube and an ammonia inlet arrange for an electric light to shine downwards into the flask. 

FIOR Process. In the FIOR process, shown in Figure 5, sized iron ore fines (0.04—12 mm) are dried in a gas-fired rotary dryer. A skip hoist dehvers the dry fines to lock hoppers for pressurizing. The fines pass through four fluidized-bed reactors in series. Reactor 1 preheats the ore to 760°C in a nonreducing atmosphere. Reactors 2, 3, and 4 reduce the ore at 690—780°C. At higher (ca 810°C) temperatures there is a tendency for the beds to defluidize as a result of sticking or hogging of the reduced material. 

Sanitizers. Spa and hot-tub sanitation is dominated by chlorine- and bromine-based disinfectants. Public spas and tubs usually employ automatic feeders, eg, CI2 gas feeders, to maintain a disinfectant residual. Private or residential spas and tubs can use automatic chemical feeding or generating devices, or they can be sanitized manually with granular or liquid products. The most widely used products for private spa and tub sanitation are sodium dichloroisocyanurate and bromochlorodimethylhydantoin. Granular products are normally added before and after use, whereas solids, eg, stick-bromine, are placed in skimmers or feeders. Bromine generating systems can also be used and are based on oxidation of bromide ions (added to the water as sodium bromide) by peroxymonosulfate, chloroisocyanurates, hypochlorites, or ozone to generate the disinfectant HOBr. 

Both friction and wear measurements have been used to study boundary lubrication of fuel because sticking fuel controls and pump failures are primary field problems in gas turbine operation. An extensive research program of the Coordinating Research Council has produced a baH-on-cylinder lubricity test (BOCLE), standardized as ASTM D5001, which is used to qualify additives, to investigate fuels, and to assist pump manufacturers (21). 

Steam-tube dryers are suitable for any particulate material that can be conditioned so as not to stick to metal when dry. Because of relatively iaexpensive heating surface and large capacities, these dryers are probably the most commonly used of the iadirect-heat dryers. Gas- and vapor-tight seals sometimes are built for operations involving dangerous vapors and iaert gas circulation, but these seals are expensive and high maintenance. Small iastaHations excepted, stationary vessels are preferable. 

The inside of the convection tubes rarely foul, but occasionally the Hquid unsaturates in feedstocks tend to polymerize and stick to the walls and thus reduce the heat transfer. This soft coke is normally removed by mechanical means. In limited cases, the coke can also be burnt off with air and steam. Normally, the outside surface of the convection section fouls due to dust and particles in the flue gas. Periodically (6 to 36 months), the outside surface is cleaned by steam lancing. With Hquid fuel firing, the surface may require more frequent cleaning. 

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