Mach number concentration

The practical and economic advantages of the use of oxygen and oxygen-enriched air over air alone, across a number of industries, typically fall into one or more of the foUowing categories. (/) Higher combustion or dame or reaction temperatures and shorter dames, yielding faster reactions at nominal reaction temperatures. Typical maximum dame temperatures using oxygen can be as high as 3033 K (5000°F), whereas for air maximum dame temperatures are usually lower by more than 555 K (1000°F). In many appHcations, higher temperatures permit faster melting or processing. In some processes the desired product or result may not even be achieved at the lower temperatures obtained using air. (2) Less waste energy in the gas or vent due gas. To recover energy, due gas is often heat-exchanged down to as low a temperature as is practical, but at the end of the heat-exchange process, the residual heat content retained in the due gas represents a loss of energy. When the nitrogen is removed, the due gas dow is reduced by about 75%, providing a distinct energy advantage. (J) Reduced volume of due gas or vent gas to treat. When gases must be treated to remove poUutants, reduced volume (no nitrogen) means that the treating devices, eg, scmbber, baghouse, or electrostatic precipitator, may be much smaller in volume and the poUutant to be removed much more concentrated. In some cases lower quaHty, lower cost fuels or feedstocks may be used because the poUutants may be more easily removed from the due gas or vent gas. (4) Reduced emissions of nitrogen oxides. The elimination of nitrogen from the combustion or process air often results in a significant reduction in the formation of nitrogen oxides such as NO, NO2, and N2O. (5) The desired product is easier to remove at the end of the process. The reduction or removal of nitrogen from the feed translates to a higher concentration of product in the plant streams and an easier separation to recover the product. (6) Economics of air compression. When oxygen or air is required at high, eg, >13,800 kPa (2,000 psi), pressure for a process, but only the oxygen reacts, it may be more economical to separate the air initially and only supply the oxygen at high pressure, saving the cost of compressing the nitrogen. (7) Nitrogen in the product is undesirable, yet caimot be removed economically.  [c.481]

Other measurements important to visual air quality are pollutant related, i.e., the size distribution, mass concentration, and number concentration of airborne particles and their chemical composition. From the size distribution, the Mie theory of light scattering can be used to calculate the scattering coefficient (20). Table 14-2 summarizes the different types of visual monitoring methods (21).  [c.209]

The supplier s general experience should be used to round out the review. Has the vendor used this corrosive gas at these concentrations Does the supplier have experience with the specified gas at the trace le% els of reactive gas, preferably at both higher and lower concentrations A n example of the trace gas found in hydrocarbons is H2S. It is very impor tant that the supplier has experience at the anticipated pressure or densit> levels. The successful operation with gases in the low Mach number range should be demonstrated by the referencing of previous installations. The compression temperatures should be well within the experience range, because this is particularly critical for reliability with reciprocating compressor valves. Hopefully, these few examples are adequate to guide the reader in the proper direction, as a more comprehensive list wouid become quite lengthy and may not cover all the area needing review.  [c.483]

The most important consideration affecting the choice of the method for locating minima, or stationary points in general, is the availability of analytical derivatives of the object fiinction, in our case the energy. Zeroth-order (energy only) methods can be used for a few variables but are notoriously inefficient for a larger number of degrees of freedom. First-order methods, which use both energy and gradient (first-derivative) infomiation, are particularly usefiil in quantum chemistry because the extra effort needed to evaluate all first derivatives is usually comparable to the calculation of the energy itself and may be less, particularly for the electronic degrees of freedom [5]. Second-order methods, which use second derivatives, fiirther improve the convergence of the optimization process. However, calculating second derivatives tends to be much more expensive than calculating the gradient, and fiill second-order methods are usually cost efficient only when first-order methods have severe convergence problems. Derivatives higher than the second have been used occasionally, but they are not generally available and are expensive to calculate. Consequently, this article will mainly concentrate on first- and second-order methods.  [c.2332]

A combination of equation (C2.6.13), equation (C2.6.14), equation (C2.6.15), equation (C2.6.16), equation (C2.6.17), equation (C2.6.18) and equation (C2.6.19) tlien allows us to estimate how low the electrolyte concentration needs to be to provide kinetic stability for a desired lengtli of time. This tlieory successfully accounts for a number of observations on slowly aggregating systems, but two discrepancies are found (see, for instance, [33]). First, tire observed dependence of stability ratio on salt concentration tends to be much weaker tlian predicted. Second, tire variation of tire stability ratio witli particle size is not reproduced experimentally. Recently, however, it was reported that for model particles witli a low surface charge, where tire DL VO tlieory is expected to hold, tire aggregation kinetics do agree witli tire tlieoretical predictions (see [60], and references tlierein).  [c.2684]

Nuclear magnetic resonance spectroscopy (chapters Bl.l 1, B1.12, B1.13 and B1.14) can provide cross-relaxation rates between two proton spins, from which a set of short range (up to 5 A) distance constraints can be generated [21], from which in turn a tliree dimensional confonnation can be computed [22, 23]. The number of constraints is much larger tlian tlie number of degrees of freedom in tlie protein, which partly compensates for tlie limited accuracy of tlie constraints (uncertainties can be as much as 1 A, but renders tlie computational problem exceedingly difficult, comparable to tlie protein folding problem (section 2.5). The upper limit of protein molecular weight is about 200 000. Since tlie intrinsic time scale of NMR is about 1 ms, as in tlie case of x-ray diffraction, many confonnations are averaged out. An attraction of tlie metliod is tliat tlie protein is not constrained in a crystal, but is presumably present in its native stmcture, altliough in order to measure signals of adequate intensity, ratlier high protein concentrations have to be used and tliere is a risk of aggregating tlie protein.  [c.2818]

Count the number of species whose concentrations appear in the equilibrium constant expressions these are your unknowns. If the number of unknowns equals the number of equilibrium constant expressions, then you have enough information to solve the problem. If not, additional equations based on the conservation of mass and charge must be written. Continue to add equations until you have the same number of equations as you have unknowns.  [c.159]

The argon gas, which flows through the concentric quartz tubes (shown in Figure 14.1) and through the high-frequency field, does not become a plasma until a few electrons have been introduced near the flame end of the concentric tubes. The following sequence of events occurs within a few milliseconds. A hot spark, usually produced piezoelectrically, contains electrons that are carried by the flowing argon gas into an oscillating high-frequency electromagnetic field, where they are accelerated rapidly back and forth by its changing magnetic and electric components. The oscillating electrons collide with neutral argon atoms, and their motions become chaotic. Nevertheless, the electrons continue to be accelerated until they gain enough energy to cause ionization of some argon atoms. At this crucial stage, more electrons and ions are produced in a cascade process (Figure 14.3), so within a few milliseconds a high concentration of ions and electrons is produced in the flowing argon gas. The result is a plasma that glows with light emitted from excited atoms and ions and from recombination of electrons with ions (see Chapter 6). This glow gives the argon plasma its characteristic pale-blue-to-lilac coloration. There are approximately equal numbers of positive ions and electrons in a plasma, so there is not much of a space charge. The number of ions and electrons reaches a number density of about 10 to 10 per milliliter.  [c.89]

A plasma flame commonly has a diameter of about 1 cm and a length of about 2-3 cm. If this flame is regarded as being approximately cylindrical, the volume of the flame at about 5300 K is 1.6 ml and at 300 K is 0.1 ml. With a specific heat for argon of 0.124 cal/g/K and a density of 1.78 x lO g/ml (at 300 K), the heat content of the flame is 0.1 cal. However, since gas flow through the hot flame occurs in a period of about 2 msec, the power output of the flame is about 50 W. This output should be compared with a power input from the high-frequency electromagnetic field of about 1 kW. The seeming inconsistency between the high temperamre and the low heat content arises because of the low number density of hot particles. (The concentration of electrons and other particles in the hot flame is approximately Ifr M.)  [c.104]

A plasma flame commonly has a diameter of about 1 cm and a length of about 2-3 cm. If this flame is regarded as being approximately cylindrical, the volume of the flame at about 5300 K is 1.6 ml and at 300 K is 0.1 ml. With a specific heat for argon of 0.124 cal/g/K and a density of 1.78 x 10 g/ml (at 3(X) K), the heat content of the flame is 0,1 cal. However, since gas flow through the hot flame occur.s in a period of about 2 msec, the power output of the flame is about 50 W. This output should be compared with a power input from the high-frequency electromagnetic field of about 1 kW, The seeming inconsistency between the high temperature and the low heat content arises because of the low number density of hot particles, (The concentration of electrons and other particles in the hot flame is approximately ICH M.)  [c.110]

A sample of the protein, horse heart myoglobin, was dissolved in acidified aqueous acetonitrile (1% formic acid in HjO/CHjCN, 1 1 v/v) at a concentration of 20 pmol/1. This sample was injected into a flow of the same solvent passing at 5 pl/min into the electrospray source to give the mass spectrum of protonated molecular ions [M + nH] shown in (a). The measured ra/z values are given in the table (b), along with the number of protons (charges n) associated with each. The mean relative molecular mass (RMM) is 16,951,09 0.3 Da. Finally, the transformed spectrum, corresponding to the true relative molecular mass, is shown in (c) the observed value is close to that calculated (16,951.4), an error of only 0.002%.  [c.292]

Numerous methods for the deterrnination of monomer purity, including procedures for the deterrnination of saponification equivalent and bromine number, specific gravity, refractive index, and color, are available from manufacturers (68—70). Concentrations of minor components are deterrnined by iodimetry or colorimetry for HQ or MEHQ, by the Kad-Eisher method for water, and by turbidity measurements for trace amounts of polymer.  [c.165]

The countercurrent arrangement (Fig. 5c) represents the best compromise between the objectives of high extract concentration and a high degree of extraction of the solute, for a given solvent-to-feed ratio. The feed entering stage 1 is brought into contact with a B-rich stream which has already passed through the other stages, while the raffinate leaving the last stage has been in contact with fresh solvent. Because of the economic advantages, continuous countercurrent extraction is normally preferred for commercial-scale operations. For the case of a partially miscible ternary system, the number of ideal stages in a countercurrent cascade can be estimated graphically on a triangular diagram, using the Hunter-Nash method (53). The feed and solvent compositions and the resulting mixture point M are first located on the diagram as in Figure 2a. If in addition one of the exit stream (extract or raffinate) compositions is given, a point representing the composition of the net flow in the countercurrent cascade can be located. This point, called the delta point, provides the basis for constmction of material balance lines and tie-lines representing a sequence of ideal stages for the countercurrent extractor. The Hunter-Nash procedure is well known and useflil (5,28). For dilute systems, it is often more convenient to use the delta point constmction on a diagram with solvent-free coordinates (5,28). In this case a rectangular diagram is plotted in which the horizontal axis is the mass fraction of the solute C on a B-free basis, and the vertical axis is the mass ratio of B to A + C.  [c.65]

The geothermal drilling industry is much smaller than that of oil and gas drilling and the active geothermal rig count is generally less than 10. Thus, there is not a commercial basis for the development of specialized materials and equipment for geothermal drilling. For a number of years, the U.S. Department of Energy has sponsored the development of high temperature drilling fluids and cements especially designed for geothermal operations (9). Efforts have been concentrated on lightweight, carbon dioxide-resistant cements, thermally conductive and scale-resistant protective liners, improved materials to control lost circulation, and bonding agents.  [c.265]

Pressure. Within limits, pressure may have Htfle effect in air-sparged LPO reactors. Consider the case where the pressure is high enough to supply oxygen to the Hquid at a reasonable rate and to maintain the gas holdup relatively low. If pressure is doubled, the concentration of oxygen in the bubbles is approximately doubled and the rate of oxygen deHvery from each bubble is also approximately doubled in the mass-transfer rate-limited zone. The total number of bubbles, however, is approximately halved. The overall effect, therefore, can be small. The optimum pressure is likely to be determined by the permissible maximum gas holdup and/or the desirable maximum vapor load in the vent gas.  [c.342]

It is the buoyancy of the bubble—particle aggregate that determines flotation, not the specific gravity of the particles or the particle size. Thus even the heaviest, eg, native gold, sp gr 19.3, and coarsest, eg, <3 mm for sylvite flotation, of the particles can be made to float if they can attach to a large enough bubble or if sufficient number of bubbles can be attached to each particle. In a loose sense, flotation can be considered a variation of a gravity separation technique. Large differences ia gravitational forces acting on mineral-laden bubbles and other (unattached) particles are exploited. It is generally preferable to float a small mass of particles, either value minerals or impurities, away from the rest of the ore. As for any other concentration method, flotation efficiency is affected by particle size, falling off at both very coarse and very fine sizes. The size range of optimum flotation is different for different mineral systems, but successful separations can be made down to 1 p.m (2,6). The 10—150 pm range is considered the best. Flotation efficiency and kinetics are a function of both the chemical and hydrodynamic (physical—mechanical) factors.  [c.412]

Off-Gas Treatment. Ozone-transfer efficiencies vary with the number of stages and are typically above 90%. However, since even a 95% ozone absorption efficiency can result in a contactor off-gas containing as much as 740 ppmw ozone (based on a 1.5 wt % feed gas), treatment is required to reduce the ozone concentration to an acceptable maximum level of 0.2 mg/m. Ozone in the vent gases from water-treatment ozone contact chambers is destroyed mainly by thermal (300—350°C for <5 s) and/or catalytic means, and sometimes by wet granular-activated carbon (GAG). Another option is recycling the off-gas to points in the water-treatment system having a high ozone demand. Dilution of ozone vent gases with air has been employed whenever practical. When oxygen is used as the feed gas, it can be recycled to the ozone-generation step however, once-through operation is common in order to avoid redrying costs.  [c.501]

Many cations have a catalytic effect on hydrolysis, although generally less than that exhibited by hydrogen ions. Hydrolysis rates as a function of pH may exhibit a minimum having higher rates occurring at low pH (H O" catalysis) and high pH (catalysis by counterion of base, eg, Na" ). For example, for sodium tripolyphosphate, the minimum hydrolysis rate occurs near pH 10, the naturally occurring pH of an STP solution, if NaOH is used to reach pH values higher than 10. The catalytic effect of cations is roughly related to the cation charge/size ratio and the cation concentration. Use of quaternary ammonium hydroxides to increase the pH does not result in increased hydrolysis rates because of poor catalysis by the large, low charged quaternary ammonium cation. Phosphatase enzymes catalyze extremely rapid hydrolysis of polyphosphates, at a rate as much as lO times faster than those without enzyme. The activity of these enzymes is highly influenced by a number of factors, including pH and metal ions.  [c.339]

Image Tone. The morphology and size of developed silver depends on factors relating to the emulsion grain as well as the method of development and composition of the developer. Developed silver is often in the form of long, narrow, cylindrical filaments. The filaments are commonly 15—25 nm in diameter but may be as large as 50—80 nm with slow-acting developers such as ascorbic acid (280). Development in environments that promote solution physical development tends to enhance the filament thickness. The filament dispersity, ie, the number of filaments per grain, depends in part on the grain size. In general, increases in the silver haUde grain size translate into increased filament dispersity. For sufftciendy small grains, development can lead to only a single filament per grain (319). In addition to grain size increases, exposure irradiance increases also have been observed to increase filament dispersity. For large grains exposed with high irradiance, a mass of developed filaments can be produced. Under an electron microscope, such filament masses resemble steel wool. In some cases the morphology of the silver haUde grain itself, as well as adsorbed chemical compounds and trace impurities, have induenced the morphology of the developed silver (320—323). At sufftciendy low concentrations of developed silver within the gelatin matrix of the coating, the spectmm of the light absorption is dependent on filament size and morphology. However, when the volume concentration of silver exceeds 3%, the coatings become visually neutral and the effect of particle size lessens (324).  [c.459]

The color concentrates are manufactured, either by incorporating dry pigment ia a compatible resia system ia a high intensity mixer, or by the classical flushing process, wherein the pigment presscake is flushed with a low melting resin, followed by cryogenic grinding of the soHd mass ia the kneader (33). The latter process is claimed to be superior for pigments that ate harder to disperse by conventional processes. Typically, the pigment content of the concentrate is between 10—50%. The resia used as a carrier needs to fulfill two principal requirements. It should have good wetting characteristics for the pigment for which it is used. Secondly, the carrier, which is usually a low melting thermoplastic, should be compatible for the thermoplastic polymer for which the concentrate is iatended. A number of other dispersants and additives ate used for the treatment of pigments to develop superior dispersion properties (34,35). Color concentrates ia the pellet form are used most widely for coloring thermoplastics, particularly low density polyethylene (LDPE). The addition of pigment ia high concentration changes properties of the carrier resia significantly. Specifically, concentrates become more difficult to melt because of the reinforcing effect of the pigment. Ideally, the melting point of concentrates should be similar to that of the unpigmented polymer. Hence, resin with a somewhat lower melting point than the target resin is chosen as a carrier resin for color concentrate.  [c.515]

Purity of toluene samples as well as the number, concentration, and identity of other components can be readily determined using standard gas chromatography techniques (40—42). Toluene content of high purity samples can also be accurately measured by freezing point, as outlined in ASTM D1016. Toluene exhibits characteristic uv, it, nmr, and mass spectra, which are useful in many specific control and analytical problems (2,43—45).  [c.187]

The dissociation constant for the first process is only 1.1 X 10 lmol at 25°C this corresponds to pKa 2.95 and indicates a rather small free hydrogen-ion concentration (cf. CICH2CO2H, p ffl 2.85) as a result of the strongly H-bonded, undissociated ion-pair [(H30)" F ]. By contrast, K2 = 2.6 X 10 lmol pK2 0.58), indicating that an appreciable number of the fluoride ions in the solution are coordinated by HF to give HF2 rather than by H2O despite the very much higher concentration of H2O molecules.  [c.815]

The most important contributions in this field were made Shinkai and coworkers [26-32J. They have embarked on an ambitious program that focuses on the uses to which calixarenes can be put. A good example, and one that represents an especially interesting study of cation com-plexation by calixarenes, deals with the extraction of uranium from sea water. The world s oceans contain a total of about 3 billion tons of uranium in the form of U02 associated with carbonate. Although this represents an enormous quantity of material, its concentration is only about 3 parts per billion, an amount that corresponds to less than 1 mg in a large-size backyard swimming pool. Also, the U02 is accompanied by numerous other cations, most of them present in a much larger concentration. Thus, the extraction of uranium from sea water poses a tantalizing challenge, which has been addressed by a number of chemists during the past decade. If the greenhouse effect proves to be responsible for adverse global changes in the climate, it may force greater attention to nuclear energy, and the recovery of uranium from sea water will become a more pressing problem in the future than it is at the present time. Early reports of U02 complexation came from the laboratories of Alberts and Cram [33] in 1976, where crown ethers chemistry was coming to fruition. Another work in this field came from Japan under the leadership of the late IwaoTabushi, who found that the macrocyclic triamine-1 is particularly effective [34], having a KasMic of for U02. This material was tested in the  [c.342]

The procedures for magnetising and particle spraying are in principle the same as for the manual test. We emphasise that the test pieces must be throughly cleaned before the applying of particles. An UV-laser beam is directed towards the test piece during testing. Its path passes a number of movable mirrors whose stepper morors make it possible to sctin the test piece in the desired marmer. Areas of no interest can be completely avoided in favour of concentrating on critical areas. The great intensity of the laser beam results in a high answer or response from the magnetic particles. The light is is in the form of a tiny spot which gives improved opportunities for the signal processing. A principal sketch is shown in Fig 2  [c.640]

The self-assembled monolayers described above are often well understood in terms of a close-packed area per molecule however, the careful determination of tilt angle and surface density is necessary to confirm these values. Dyes have received much attention because of the ease of obtaining accurate concentrations colorimetrically. While dye adsorption generally follows the Langmuir equation, multilayer adsorption can occur. Additional problems that may arise due to dye association in solution are discussed by Padday [133] and Barton [134]. Rahman and Ghosh [135] used the Langmuir adsorption of pyridine (molecular area 24 A ) on various oxides to determine surface areas. Pugh [136] has used a number of acid and base probe molecules to identify chemical sites on several minerals used as polymer fillers. Surface areas may be estimated from the exclusion of like-charge ions from a charged interface [137]. This method is intriguing in that no estimation of site or molecular area is called for. Area determination with binary liquid systems (see next section) has been proposed by Everett [138] and discussed by Schay and Nagy [139].  [c.406]

Considering a large number of ions with parallel trajectories impinging on a target atom, the ion trajectories are bent by the repulsive potential such that there is an excluded volume, called the shadow cone, in the shape of a paraboloid fomied behind the target atom as shown in figure B1.23.3(a). Ion trajectories do not penetrate into the shadow cone, but instead are concentrated at its edges much as rain pours off an umbrella. Atoms located inside the cone behind the target atom are shielded from the impinging ions. Similarly, if the scattered ion or recoiling atom trajectory is directed towards a neighbouring atom, that trajectory will be blocked. For a large number of scattering or recoiling trajectories, a blocking cone will be fomied behind the neighbouring atom into which no particles can penetrate, as shown in figure B1.23.3(T)). The dimensions of the shadowing and blocking cones can be detemiined experimentally from scattering measurements along crystal azimuths for which the interatomic spacings are accurately known.  [c.1804]

Collision processes involving the different plasma components play an important role in non-thennal plasmas (table C2.13.1) [13, 14 and 15]. Electron collision processes are of particular importance because of the high temperature or high mean energy of the plasma electrons. Stepwise excitation and ionization, that is the excitation/ionization of an atom or molecule which is already in an excited or, in particular, in a metastable state, can occur with appreciable probability even though the concentration of excited/metastable species in a non-thennal plasma is generally low. The energy spacing between excited states is typically much smaller than the energy gap between the ground state and the first excited state. The number of low-energy electrons is typically much higher than the number of electrons with energies above about 10 eV and the excitation/ionization cross section out of an excited state is much larger than the cross section for excitation/ionization of ground-state species. This may result in rate coefficients (see below) for stepwise excitation/ionization that are quite large. Metastable species cannot decay via radiative dipole transitions to lower states. This results in a comparatively long lifetime of microseconds or even milliseconds for these species (compared to nanoseconds for excited states which can decay radiatively via dipole transitions). As a consequence, metastables can accumulate in the plasma and can be an efficient source of species for stepwise excitation/ionization processes or for super-elastic collisions in which the scattered electron gains energy. Ionization due to binary collisions involving metastable atoms or molecules is an efficient mechanism for charge carrier production. The generation of free radicals by electron collisions in molecular plasmas is an important precursor for plasma chemical reactions. Electron impact ionization is the fundamental process for sustaining a non-thennal plasma. Electron-impact-induced dissociation leading to the fonnation of free radicals is the most important reaction channel in plasma chemistry. In conventional chemistry, the fonnation of radicals is detennined by the temperature of the entire system offering a different spectmm of secondary reactions from that resulting from radical production by electron collision in the cold neutral gas environment of a non-thennal plasma.  [c.2798]

In order to predict the overall chemical reaction rate In a catalyst pellet, it is necessary to be able to write down correct differential material balances, which can then be Integrated to give the required re action rate or effectiveness factor, There is, of course, an enormous literature on this subject, but surprisingly the great majority of this is confined to one or two rather unrealistic special cases. Much the largest number of papers use flux relations applicable only to binary mixtures, and may slip implicitly Into further constraints which limit the validity of their material balances to a simple isomerization A B. Nevertheless, the resulting differential eouatlons are often used to determine the concentration profile of one component In a multicomponent mixture. Certain papers formulate material balances which are correct for any reaction of the form A nB (where n is not necessarily unity), provided all pores are large compared with the mean free path lengths. Others formulate balances which are correct In multicomponent mixtures, but only when all pores are narrow compared with the mean free path lengths, so that Knudsen diffusion controls. In realistic situations, however, the reaction mixture is very rarely binary and the pore size distribution Is commonly either very broad or bimodal, with Knudsen diffusion controlling in the smallest pores and the larger pores of such a size that the diffusion mechanism lies in the intermediate range between the extremes of Knudsen and bulk diffusion control. When the distribution is strongly bimodal and the micropores are predominantly dead-ended, their Influence can be taken Into account simply by defining a modified reaction rate function relating the total reaction rate per unit pellet volume to the local composition in the macropore system. Using appropriate flux relations for the macropores, it should then be possible to predict the Influence of pellet dimensions and macropore structure on the overall reaction rate. However, to accomplish even  [c.110]

Finite element solution of engineering problems may be based on a structured or an unstructured mesh. In a structured mesh the form of the elements and local organization of the nodes (i.e, the order of nodal connections) are independent of their position and are defined by a general rule. In an unstructured mesh the connection between neighbouring nodes varies from point to point. Therefore using a structured mesh the nodal connectivity can be implicitly defined and explicit inclusion of the connectivity in the input mesh data is not needed. Obviously this will not be possible in an unstructured mesh and nodal connectivity throughout the computational grid must be specified as part of the input data. It is important, however, to note that stnictured computational grids lack flexibility and hence are not suitable for engineering problems which, in general, involve complex geometries. Discretization of domains with complicated boundaries using structured grids is likely to result in badly distorted elements, thus precluding robust and accurate numerical solutions. Using an unstructured mesh, geometrical complexities can be handled in a more natural manner allowing for local adaptation, variable element concentration and preferential resolution of selected parts of the problem domain. However, because of the inherent complexity of data handling in unstructured mesh generation this approach requires special programs for the organization and recording of nodes, element edges, surfaces, etc. which involve extra memory requirement. In particular, any increase in the number of elements during mesh refinement requires rapidly rising computational efforts. A further drawback for unstructured grids is the difficulty of handling moving boundaries in a purely Lagrangian approach in the simulation of flow problems.  [c.192]

A plasma flame commonly has a diameter of about 1 cm and a length of about 2-3 cm. If this flame is regarded as approximately cylindrical, the volume of the flame at about 5300 K is 1.6 ml and at 300 K is 0.1 ml. With a specific heal for argon of 0.124 cal/g/K and a density of 1.78 x ICf g/ml (at 300 K), the heat content of the flame is 0.1 cal. However, since gas flow through the hot flame occurs in a period of about 2 msec, the power output of the flame is about 50 W. This output should be compared with a power input from the high-frequency electromagnetic field of about 1 kW. The seeming incon.sistency between the high temperature and the low heat content arises because of the low number density of hot particles. (The concentration of electrons and other particles in the hot flame is approximately ICf M.)  [c.98]

In large plates 0.61 m or more in diameter, the efficiency of the tray as a whole may differ from the efficiency observed at some particular point of the tray because the Hquid is not uniformly mixed in the direction of the flow on the whole tray. The point value of the efficiency called Eqq is thus more closely related to interphase diffusion than As the gas passes upward through the Hquid covering a small area of the plate, mass transfer from gas to Hquid occurs in a manner similar to a packed tower of height h-Q the depth of the bubbling area. Under the assumption that the Hquid is completely mixed in the vertical direction, and that the gas travels through that minicolumn in a plug-flow-like fashion, the number of transfer units of the bubbling area may be calculated in terms of the gas concentrations above and below the area under consideration by applying the definition of Nqq, equation 55. This equation may be integrated by takings as constant and equal tojy because of the weU-mixed nature of the Hquid phase. By comparing the result with the definition of the plate efficiency, equation 82, formulated for a single point on the plate, the foUowing relationship between the point efficiency and the number of transfer units arises  [c.42]

Sulfur. Sulfur occurs in plants at levels as high as that of phosphoms. It is absorbed by plants as the sulfate anion, SO , which is a constituent of many fertilizers. Normal superphosphate contains much calcium sulfate [7778-18-9]. Ammonium sulfate is a good source. Wet-process phosphoric acid often contains a few percent of sulfur as sulfuric acid and calcium sulfate, and this sulfur appears in fertilizers, such as ammonium phosphates, made from the acid. Other sources of sulfur in soils are decreasing. In industrialized, humid regions sulfur additions to the soil from rain range from 28 to 168 kg/hm yearly. Soils in such regions do not often show deficiency in sulfur, but as environmental goals of eliminating sulfur oxide emissions from industrial plants are met (see Exhaust control, INDUSTREAl), sulfur deficiency in soils can be expected to increase. AH indications are that fertilizers need to contain increa sing amounts of sulfur. In fact, symptoms of sulfur deficiency in soils of the United States have been increasing for some years. Sulfur deficiency had been identified in 13 states in 1960 the number grew to 31 states by 1973. The average sulfur concentration of fertilizers in the United States has been decreasing since the 1950s as the average NPK grade of fertilizers has increased.  [c.242]

Development Based on Natural Products. Development, with or without the use of QSAR, of herbicides from natural products has been rare. Although a number of natural products have shown herbicidal activity, specificity has been lacking, the effective concentration has proven too high for practicaHty, or the cost of manufacture on a mass scale has been considered prohibitive. These characteristics have led to a variant of the lead-compound approach in which the microorganisms, usually fungi, that produce the biologically active natural products are appHed to the weed in the form of mycoherbicides(20—22), ie, herbicides based on fungal weed pathogens. The principal advantage of mycoherbicides over conventional herbicides is the relative ease of registration. The principal disadvantage is very limited target specificity a mycoherbicide is usually effective against only one weed species under rather specific environmental conditions. Future commercial development of mycoherbicides depends heavily on improvements in the formulations that are necessary for increased shelf-life and vitaHty of the living fungal spores that constitute the active ingredient of this type of pesticide (23).  [c.39]

Dextran [9004-54-0] is a term that has traditionally been appHed to any extracellular bacterial a-D-glucan synthesized from sucrose [57-50-1] in which a(l — 6) linkages predominate. Dextrans have been more strictiy defined as D-glucans containing chains of D-glucopyranosyl residues consecutively a(l — 6)-linked, with various degrees of branching through a(l — 2), a(l — 3), or a(l— 4) linkages (66). Dextran has been known for many years, and was recognized as a polymer of dextrose (D-glucose) by the latter half of the nineteenth century, hence the origin of the name. Dextran research has been reviewed (66—73), and a bibHography has been pubHshed (74). A number of lactic acid bacteria produce dextrans (75), the most notable being l euconostoc mesenteroides and certain Streptococcus species. Much of the early interest in dextrans arose as a result of its occurrence in sugar (qv) refineries. Infection of sugar cane, and to a lesser extent, sugar beets, by E. mesenteroides during harvesting and processing leads to the production of dextran. Large amounts can give rise to sticky, gummy solutions that foul processing equipment, whereas lesser concentrations inhibit proper crystallization of sugar (71). Food preparations that contain sucrose can also become contaminated by growths of dextran-producing bacteria, leading to sliminess, gumminess, or "ropy" solutions.  [c.296]

Pharmaceuticals. The concept of microencapsulation has intrigued the pharmaceutical industry for many years, because it offers the possibihty of providing a number of important new oral and parenteral dosage forms. Microcapsules in oral dosage forms could conceptually taste-mask bitter pharmaceuticals, provide extended release in vivo, provide enteric release, improve the stabiUty of incompatible dmg mixtures, provide resistance to oxidation, reduce volatiUty, and distribute a dmg in many small carrier particles so that effects of the dmg on the sensitive walls of the stomach ate minimized. Microencapsulated parenteral formulations could provide prolonged deUvery of dmgs with short half-Hves in vivo and perhaps even achieve targeted dmg deUvery. For these reasons, microencapsulation has received much attention by pharmaceutical scientists (44). Several mictocapsule-based oral pharmaceutical formulations which offer some of these features ate available. AH have an ethylceUulose shell and ate produced by a polymer—polymer phase-separation process carried out in hot cyclohexane (8). The cote material is a soHd that has finite solubiUty in water. Encapsulated potassium chloride, KCl, has been used extensively because the KCl dispersed in many small ethylceUulose capsules minimizes high localized concentrations of KCl in the stomach that can irritate the lining of the stomach and induce bleeding. Aspirin encapsulated in ethylceUulose for arthritic patients is an example of using microencapsulation to extend time of release of a dmg in the gastrointestinal tract (see Gastrointestinal agents). In this case, the encapsulated aspirin formulation provides overnight reUef FinaUy, encapsulated oral acetaminophen formulations for chUdren ate used to provide taste-masking.  [c.324]

A number of nonionic and anionic polymers are employed in water-based muds to stabilize shales. These may be added to a freshwater mud or to a system containing one of the salts mentioned. Historically, high (>30 kg/m ) concentrations of chrome lignosulfonates were thought to stabilize hydratable shales. This technique rarely is used in the 1990s. Typically, shale-stabilization polymers iaclude modified starches (78) ceUulosic polymers such as CMC and HEC gums such as guar, xanthan (104), and flax meal (105) and high molecular weight polyacrylamides of varying degrees of hydrolysis (9,53,106). A fluid containing a combination of potassium siUcate [1312-76-1] and poly(vinyl alcohol) [9002-89-5] has also been used (107). The consumption of these materials for shale stabilization is difficult to estimate because they may also be used for viscosity or filtration control. Nonionic polymers are typically used at concentrations of 3 to 11 kg/m (1—4 lb/bbl) anionic polymers can often be effective at much lower (0.5 to 3 kg/m  [c.182]

Colorants can be introduced into the fiber by adding dyes and pigments in salt preparation, during polymerization, or into the molten polymer just before spinning (148) (see CoLORANTS FORPLASTics Dyes, application and evaluation). Pigmented fibers are referred to as mass-dyed, dope-dyed, solution-dyed, or producer-colored. Inorganic pigments are used more than the organics, especially where high color, light-, and crock fastness are required, such as in upholstery and carpet for automotive interiors. The organic pigments have higher chroma, but are not as colorfast to heat and light (see Pigments). Nylon-6 can accommodate more pigments than nylon-6,6 because of its lower melt processing temperatures. Like Ti02, the pigments must be dispersible and heat stable in polymer and fiber manufacturing (149). A common and efficient approach to adding pigment to the base polymer in spinning is first to disperse the pigment as a concentrate in a carrier polymer, usually a lower melting copolymer. The concentrates range from 25 to 50% pigment content and are offered as a single color or a compounded color blend in pellet or flake form. The flake can be blended with the base polymer flake at a specified loading and charged to the feed hopper of the spinning process or remelted in a vessel that allows it to be metered directly into the molten polymer prior to spinning. QuaUty pigmented fibers are spun with processes equipped with mixing screws and volumetric or gravimetric automatic feeders. Typical pigments for nylon are carbon black, red iron oxide, aluminum cobalt blue, and phthalocyanine blue and green. Carbon black enhances nylon s resistance to photodegradation. A number of light-stable pigments that are also environmentally friendly are available (150).  [c.257]

A protonic acid derived from a suitable or desired anion would seem to be an ideal initiator, especially if the desired end product is a poly(tetramethylene oxide) glycol. There are, however, a number of drawbacks. The protonated THF, ie, the secondary oxonium ion, is less reactive than the propagating tertiary oxonium ion. This results in a slow initiation process. Also, in the case of several of the readily available acids, eg, CF SO H, FSO H, HCIO4, and H2SO4, there is an ion—ester equiUbrium with the counterion, which further reduces the concentration of the much more reactive ionic species. The reaction is illustrated for CF SO counterion as follows  [c.362]

Air Monitoring. The atmosphere in work areas is monitored for worker safety. Volatile amines and related compounds can be detected at low concentrations in the air by a number of methods. Suitable methods include chemical, chromatographic, and spectroscopic techniques. For example, the NIOSH Manual of Analytical Methods has methods based on gas chromatography which are suitable for common aromatic and aHphatic amines as well as ethanolamines (67). Aromatic amines which diazotize readily can also be detected photometrically using a treated paper which changes color (68). Other methods based on infrared spectroscopy (69) and mass spectroscopy (70) have also been reported.  [c.264]

Fertilizers. The fertiliser industry constitutes the largest market for ammonia and direct appHcation of anhydrous ammonia represents the largest single consumption. Some of the advantages (98) of anhydrous ammonia are (/) Having 82% nitrogen, it is the most concentrated nitrogen fertiliser available. (2) It improves soil tilth, increasing the water-holding capacity, and decomposes crop residue and organic matter. (2) It is appHed 150—200 mm deep or at plow depth, expanding laterally to form a band measuring about 200 mm wide. AppHed in the form of a slug, or mass, this increases the efficiency for great uptake of nitrogen by crop root. It increases the number, sise, and strength of crop roots resulting in deeper penetration, greater plant development, and abiHty to withstand periods of drought. (4) It is easy to apply it flows under its own pressure from the appHcator tank to the soil. (5) It combines with clay and organic matter to resist leaching losses. 6) It can be appHed at various times, fall, winter, or spring as a pre-plant, or in the summer as a sidedress appHcation. ( 7) It releases other plant food elements that are present in the soil, such as potassium, phosphoms, calcium, and magnesium.  [c.358]

See pages that mention the term Mach number concentration : [c.32]    [c.127]    [c.484]    [c.1740]    [c.1933]    [c.400]    [c.68]    [c.78]    [c.95]    [c.542]    [c.445]   
Pressure safety design practices for refinery and chemical operations (1998) -- [ c.350 ]