Exhaust wall jet-enhanced


The most economical and successful solutions to lAQ problems tend to be those in which the operating principle of the correction strategy makes sense and is suited to the problem. If a specific point source of contaminants has been identified, treatment at the source (e.g., by removal, scaling, or local exhaust) is almost always a more appropriate correction strategy than dilution of the contaminant by increased general ventilation. If the lAQ problem is caused by the introduction of outdoor air that contains contaminants, increased general ventilation will only make the situation worse (unless the outdoor air is cleaned). It is important to make sure that one understands the lAQ problem well enough to select a correction strategy whose size and scope fit the job. If odors from a special use area such as a kitchen are causing complaints in a nearby office, increasing the ventilation rate in the office may not be a successful approach. The mitigation strategy should address the entire area affected.  [c.234]

Rotary Driers The rotary drier is basically a cylinder, inclined slightly to the horizontal, which may be rotated, or the shell may be stationary, and an agitator may revolve slowly. In either case, the wet material is fed in at the upper end, and the rotation, or agitation, advances the material progressively to the lower end, where it is discharged. Figure 35 illustrates a direct- heat rotary drier. Typical dimensions for a unit like this are 9 ft in diameter and 45 ft in length. In direct-heat, revolving rotary driers, warm air or a mixture of flue gases and air travels through the cylinder. The rate of feed, the speed of rotation or agitation, the volume of heated air or gases, and their temperature are so regulated that the solid is dried just before discharge. The shell fits loosely into a stationary housing at each end. The material is brought to a chute that runs through the housing the latter also carries the exhaust pipe. The revolving shell runs on two circular tracks and is turned by a gear that meshes with a driven pinion. The inclination is one in sixteen for high capacities and one in thirty for low ones. As the shell revolves, the solid is carried upward one-fourth of the circumference it then rolls back to a lower level, exposing fresh surfaces to the action of the heat as it does so. Simple revolving rotary driers serve well enough when fuel is cheap. The efficiency is greatly improved by placing longitudinal shelves 3 or 4 in. wide on the inside of the cylinder. Longitudinal shelves are called lifting flights. The shelves carry part of the solid half-way around the circumference and drop it through the whole of a diameter in the central part of the cylinder where the air is hottest and least laden with moisture. By bending the edge of the shelves slightly inward, some of the material is delivered only in the third quarter of the circle, producing a nearly uniform fall of the material throughout the cross section of the cylinder. The heated air streams through a rain of particles. This is the most common form of revolving rotary cylinder. It has great capacity, is simple in operation, and is continuous.  [c.139]

If the world were perfect, a researcher could tell her PC to calculate the exact solution to the Schrodinger equation and continue with the rest of her work. However, the exact solution to the Schrodinger equation has not yet been found and ah initio calculations approaching it for moderate-size molecules would be so time-consuming that it might take a decade to do a single calculation, if a machine with enough memory and disk space were available. However, many methods exist because each is best for some situation. The trick is to determine which one is best for a given project. The first step is to predict which method will give an acceptable accuracy. If timing information is not available, use the scaling information as described in the previous chapter to predict how long the calculation will take.  [c.136]

A concentrated solution of 3 mol of lithium acetylide in 1.4 1 of liquid ammonia was prepared (see Ref. 1) from lithium amide and acetylene, in the presence of a small amount of triphenylmethane. The solution was cooled to -75°C (internal temperature) by means of a liquid nitrogen bath. During this cooling the mixture was vigorously agitated in order to prevent solidification of the ammonia on the walls. At the same time nitrogen was introduced at a rate of 400 ml/min. When the mixture had attained the prescribed temperature, addition of acrolein or croton-aldehyde (2.6 mol freshly distilled) was started, while a vigorous stream of nitrogen was passed through the flask (1.5-2 1/min). The aldehydes were added over 15-20 min with vigorous stirring. Continuous cooling was not necessary as the reactions were not very exothermic. After the addition the cooling bath was removed and the introduction of N2 stopped. The mixture was allowed to stand for 30 min, then it was cautiously poured into a 5-1 wide-necked round-bottomed flask. Ammonium chloride (3 mol) was introduced as quickly as possible in 1-g portions with manual swirling. The ammonia was evaporated by placing the flask in a water bath of 50-60°C. During this evaporation the flask was continuously swirled by hand in Order to suppress bumping. To the slurry (still containing ammonia) which remained, crushed ice, just enough to dissolve the solids, was cautiously added (with swirling). The reaction flask was washed with a small amount (50 ml) of ice-water and this washing was added to the main portion. The mixture was extracted with diethyl ether 10 times in the case of R = CH3, at least 15 times in the case R = H (if desired, continuous extraction can be carried out). The unwashed extracts (note 1) v/ere dried over 100 g of magnesium sulfate. This was filtered off on a sintered-glass funnel and thoroughly rinsed with ether. The greater part of the diethyl ether was distilled off at normal pressure through a 40-cm Vigreux column, avoiding bath temperatures higher than OO C. The remaining liquid (note 2) was distilled very quickly through the same column, the (single) receiver being cooled in ice + ice-water (see Chapter I, Fig. 5). An aqueous forerun mainly consisting of carbinol was trapped in this manner. During the distillation of the acrolein--carbinol the bath temperature should not exceed 90-100°C the viscous residue in this case was subjected to a distillation at very low pressure (< 0.5 mmHg), whereby the (single) receiver was cooled below -40°C, in this way a second crop of carbinol was obtained. Practically no residue remained after the distillation of the crotonaldehyde-carbinol.  [c.79]

The Modified Chemical Vapor Deposition (MCVD) process (Fig. 21) involves reactions within a glass tube and glass deposition on the inside walls of this tube. A rotating, conventionally fabricated, siHca glass tube is heated with an oxy-hydrogen torch to cause vapor-phase oxidation of the metal haHde gases which are flowing inside. Ultimately, the tube becomes the outer part of the fiber cladding, and the deposited soot becomes the fiber core. Using a conventional glass tube as part of the fiber can produce fiber of lower strength and higher attenuation. As the hot soot flows downstream, it is attracted to the cold walls of the tube where it is deposited as a thin porous layer, not unlike the porous OVD preform stmcture described earlier. The torch is steadily moved toward this downstream portion of the tube and, as it passes over the soot deposit, it zone-sinters it to a clear, bubble-free glass layer. When the torch reaches the exhaust end of the tube, it is quickly returned to the inlet end, and the process is repeated. After the required number of passes, enough glass is deposited on the inside wall of the tube. Then the torch traverses the tube, which softens and coUapses to a soHd rod blank. This is then drawn into fiber.  [c.313]

The required high combustion temperatures can be achieved by preheating the combustion air to temperatures of 1650—1950 K. The highest efficiencies are obtained by direct high temperature preheat of the combustion air with the MHD exhaust gas, but this requires the use of high temperature refractory heat exchangers, which are not commercially available. The requisite combustion temperatures can also be attained by enriching the combustion air with oxygen and preheating the oxygen-enriched air to more moderate temperatures, which can be reached ia conventional metal tubular heat exchangers (see HeaT-EXCHANGETECHNOLOGy). The resultant plant efficiencies are high enough to make this latter method attractive for use ia first generation commercial plants based on available technology. High temperature refractory heat exchangers would allow realization of the hiU efficiency potential of MHD as well as improved fuel utiliza tion, and even lower energy costs (see Refractories).  [c.412]

For this purpose, first of all, this model must be universal enough for the exact approximation the whole series of analytical signals and description of analytical signals in the research range of determined component concentration.  [c.30]

The purpose of a surge arrester is to safeguard a system against probable transient conditions, particularly those that may exceed the. safe impulse withstand level of the equipment. A brief criterion to determine the protective level of an arrester is given in Table 18.3. The spark-over voltage refers to conventional type gapped arresters, while the residual voltage refers to gapless type surge arresters. An arrester must protect the terminal equipment against each kind of transient condition separately. Its protective level must therefore be checked separately for all such transient conditions. While for a lightning and switching surge, it would be enough to define it by its amplitude, the FOW will be defined by its amplitude and the front time,  [c.596]

Equation (12-17) is called the photostationary state expression for ozone. Upon examination, one sees that the concentration of ozone is dependent on the ratio NO2/NO for any value of k. The maximum value of k is dependent on the latitude, time of year, and time of day. In the United States, the range of k is from 0 to 0.55 min T Table 12-5 illustrates the importance of the NO2/NO ratio with respect to how much ozone is required for the photostationary state to exist. The conclusion to be drawn from this table is that most of the NO must be converted to NO2 before O3 will build up in the atmosphere. This is also seen in the diurnal ambient air patterns shown in Fig. 12-2 and the smog chamber simulations shown in Fig. 12-3. It is apparent that without hydrocarbons, the NO is not converted to NO2 efficiently enough to permit the buildup of O3 to levels observed in urban areas.  [c.173]

If pressure drop is high enough to exceed the critical ratio, sonic velocity will be reached. When K = 1.4, ratio = 0.53.  [c.12]

The initial model will contain errors. Provided the protein crystals diffract to high enough resolution (better than 2.5 A), most of the errors can be removed by crystallographic refinement of the model. In this process the model is changed to minimize the difference between the experimentally observed diffraction amplitudes and those calculated for a hypothetical crystal containing the model instead of the real molecule. This difference is expressed as an R factor, residual disagreement, which is 0.0 for exact agreement and around 0.59 for total disagreement.  [c.383]

The second reason for modification of the displaced volume is that in real world application, the cylinder will not achieve the volumetric performance predicted by Equation 3.4. It is modified, therefore, to include empirical data. The equation used here is the one recommended by the Compressed Air and Gas Institute [1], but it is somewhat arbitrary as there is no universal equation. Practically speaking, however, there is enough flexibility in guidelines for the equation to produce reasonable results. The 1.00 in the theoretical equation is replaced with. 97 to reflect that even with zero clearance the cylinder will not fill perfectly. Term L is added at the end to allow for gas slippage past the piston rings in the various types of construction. If, in the course of making an estimate, a specific value is desired, use, 03 for lubricated compressors and. 07 for nonlubricated machines. These are approximations, and the exact value may vary by as much as an additional. 02 to. 03  [c.57]

The best anti-surge control is the simplest and most basic that will do the job. The most obvious parameter is minimum-flow measurement, or if there is a relatively steep pressure-flow characteristic, the differentia pressure may be used. The latter parameter allows for a much faster response system, as flow measurement response is generally slow however, the speed of response need only be fast enough to accept expected transients. One major problem with the conventional methods of measurement and control is the need to move the set point for initiation of the control signal away from the exact surge point to allow some safety factor for control response time and other parameters not directly included  [c.364]

The principle images produced in the SEM are of three types secondary electron images, backscattered electron images, and elemental X-ray maps. Secondary and backscattered electrons are conventionally separated according to their energies. They are produced by different mechanisms. When a high-energy primary electron interacts with an atom, it undergoes either inelastic scattering with atomic electrons or elastic scattering with the atomic nucleus. In an inelastic collision with an electron, some amount of energy is transferred to the other electron. If the energy transfer is very small, the emitted electron will probably not have enough energy to exit the surface. If the energy transferred exceeds the work function of the material, the emitted electron can exit the solid. When the energy of the emitted electron is less than about 50 eV, by convention it is referred to as a secondary electron (SE), or simply a secondary. Most of the emitted secondaries are produced within the first few nm of the surface. Secondaries produced much deeper in the material suffer additional inelastic collisions, which lower their energy and trap them in the interior of the solid.  [c.72]

To produce amorphous transparent mouldings, mould temperatures should be kept well below the Tg, a temperature of less than 50°C generally being recommended. Providing that wall thicknesses do not exceed 5-6 mm the melt cools very rapidly and there is not enough time for significant crystallisation to occur in the short time interval that the material is between T and Tg. With thicker sections it may not be possible to extract the heat out of the melt at a sufficient rate and some crystallisation may occur. It is also important to use grades which do not contain additives that accelerate crystallisation. Amorphous mouldings should not be used above Tg.  [c.721]

The model of crazing failure has been compared with experimental results obtained in a number of systems. The most direct tests have been obtained by measurement of the fracture toughness of interfaces between immiscible polymers that have been toughened by placing a known amount of diblock copolymer at the interface. The immiscible polymers were chosen so that the interface had low toughness without diblock and the diblock chosen so that each molecule could be expected to act as a single stitch between the bulk polymers, so one block was miscible in each of the homopolymers. The main systems studied have been (1) polystyrene (PS)-polymethylmethacrylate (PMMA) diblock copolymers joining PS and PMMA homopolymers or polyphenylene ether (PPE) and PMMA homopolymers, and (2) PS-PVP (polyvinyl pyridine) copolymers Joining PS and PVP homopolymers. Typical results, shown in Figs. 6 and 7, agree well with the predictions of Eq. 8 (and often the simpler Eq. 7) over a wide range of E and toughness. It is clear that the model works well when the molecular level failure process is chain scission, but not enough experimental data exist to be confident of its applicability when the failure is by chain pull-out. The chain scission force /b has been estimated to be in the range of 1.2-4 nN, where the main uncertainty  [c.230]

With such a wide variety of products using PSAs as the attachment mechanism, it is not surprising to learn that a large number of specific tests exist in the industry. These tests are usually focused on critical aspects of product performance Is the automotive masking tape adhesive strong enough to hold the masking apron in place during the vehicle s trip through the paint bake oven Does the medical tape adhere effectively to the skin and yet remove without causing much discomfort Will the truck graphic stay in place for the life of the product despite varying environmental conditions To answer these questions one needs a battery of specially designed tests, often run in parallel with more fundamental adhesion tests. Only these latter tests will be addressed here.  [c.468]

If mechanical equipment is needed to correct the lAQ problem, it must be powerful enough to accomplish the task. For example, a local exhaust system should be strong enough and close enough to the source so that none of the contaminant is drawn into nearby returns and recirculated. A mitigation strategy will be most successful when it is institutionalized as part of normal building operations. Solutions that do not require exotic equipment are more likely to be successful in the long run than approaches that involve unfamiliar concepts or delicately maintained systems. If maintenance or housekeeping procedures or supplies must change as part of the mitigation, it may be necessary to plan for additional staff training, new inspection checklists, or modified purchasing practices. Operating schedules for HVAC equipment may also require modification.  [c.234]

Ultraviolet light has been known to kill pathogens for a long time. A low pressure mercury bulb emits between 30 to 90 % of its energy at a wave length of 253.7 nm, right in the middle of the UV band. If water is exposed to enough light, pathogens will be killed. The problem is that some pathogens are hundreds of times less sensitive to UV light than others. The least sensitive pathogens to UV are protozoan cysts. Several studies show that Giardia will not be destroyed by many commercial UV treatment units. Fortunately, these are the easiest pathogens to filter out with a mechanical filter. The efficiency of UV treatment is very dependent on the turbidity of the water. The more opaque the water is, the less light that will be transmitted through it.  [c.41]

Bacteria - Bacteria are another important elass of fungi. Again numerous smaller groupings are possible. Among the higher organisms in this group are the iron, manganese and sulphur baeteria. These higher baeteria gain their energy from the oxidation of simple organic substances. Lower forms of baeteria ean be grouped as those that are helpful and those that are harmful to man. Those harmful to man are mainly the disease-produeing organisms. Helpful organisms hasten the proeess of decomposing organic matter and by feeding on waste material they aid in the purifying of water. All baeteria are sensitive to the temperature and pH of water. Some baeteria ean tolerate aeid water. But for the most part, they thrive best in waters that have a pH between 6.5 to 7.5, that is essentially neutral waters. As to temperature, most pathogenie or disease baeteria thrive best in water of body temperature. Beyond this no hard and fast statements ean be made. Some bacteria are more resistant to heat than are others. Some are more sensitive to eold. At low temperatures, for example, some baeteria may beeome dormant for long periods of time but will still continue to exist. Interestingly enough, the waste products of their own growth ean hamper baeteria and may even prove toxic to them.  [c.43]

The polyad concept is evidently a very simple but powerfiil tool in tlie analysis and description of the internal dynamics of molecules. This is especially fortunate in larger molecules, where the intrinsic spectral complexity grows explosively with the number of atoms and degrees of freedom. Does the polyad number ever break down Strictly speaking, it must the polyad number is only an approximate property of a molecule s dynamics and spectrum. The actual molecular Flamiltonian contains resonance couplings of all fomis, and these must destroy the polyad numbers at some level. This will show up by looking at high enough resolution at a spectrum which at lower resolution has a good polyad number. Levels will be observed of small intensity, which would be rigorously zero if the polyad numbers were exact. The fine detail in the spectrum corresponds to long-time dynamics, according to the time-energy uncertainty relation [49].  [c.74]

At this point it is important to make some clarifying remarks (1) clearly one caimot regard dr in the above expression, strictly, as a mathematical differential. It caimot be infinitesimally small, since dr much be large enough to contain some particles of the gas. We suppose instead that dr is large enough to contain some particles of the gas but small compared with any important physical lengtii in the problem under consideration, such as a mean free path, or the length scale over which a physical quantity, such as a temperature, might vary. (2) The distribution fiinction / (r,v,t) typically does not describe the exact state of the gas in the sense that it tells us exactly how many particles are in the designated regions at the given time t. To obtain and use such an exact distribution fiinction one would need to follow the motion of the individual particles in the gas, that is, solve the mechanical equations for the system, and then do the proper countmg. Since this is clearly impossible for even a small number of particles in the container, we have to suppose that / is an ensemble average of the microscopic distribution fiinctions for a very large number of identically prepared systems. This, of course, implies that kinetic theory is a branch of the more general area of statistical mechanics. As a result of these two remarks, we should regard any distribution fiinction we use as an ensemble average rather than an exact expression for our particular system, and we should be carefiil when examining the variation of the distribution with space and time, to make sure that we are not too concerned with variations on spatial scales that are of the order or less than the size of a molecule, or on time scales that are of the order of the duration of a collision of a particle with a wall or of two or more particles with each other.  [c.666]

The simulations also revealed that flapping motions of one of the loops of the avidin monomer play a crucial role in the mechanism of the unbinding of biotin. The fluctuation time for this loop as well as the relaxation time for many of the processes in proteins can be on the order of microseconds and longer (Eaton et al., 1997). The loop has enough time to fluctuate into an open state on experimental time scales (1 ms), but the fluctuation time is too long for this event to take place on the nanosecond time scale of simulations. To facilitate the exit of biotin from its binding pocket, the conformation of this loop was altered (Izrailev et al., 1997) using the interactive molecular dynamics features of MDScope (Nelson et al., 1995 Nelson et al., 1996 Humphrey et al., 1996).  [c.44]

Imposition of the first condition is as discussed before and the second condition is again satisfied by setting the boundary line integral (i.e. Nj a n dr in Equation (3.58) to zero. We note that along the exit line components n of are (1,0) and hence in this case the nomial component of the surface force, expressed as = -/ + 2ri(dvrJdx) will be set to zero. In addition, along the exit line (dv Jdy) 0, which using the incompressible continuity equation gives (Ov ldx) = 0. Therefore setting = 0 implies a pressure datum of zero at the domain outlet. This also shows that if the normal component of surface force is not given at any part of the domain boundary then zero pressure at a single node may be imposed as a datum, The setting of pressure boundary conditions is, in general, inconsistent with the incompressibility constraint and should be avoided. In the specific case where the pressure in a single node is prescribed, the continuity equation relating to that node should be removed from the set of discretized equations to avoid algebraic inconsistency. The validity of imposing fully developed exit boundary conditions in a flow model depends on factors such as the type of elements used, number of element layers between the inlet and outlet, inlet and wall boundary conditions and generally on fluid viscosity. Inappropriate imposition of developed flow conditions at a domain outlet reduces the accuracy of the solution and may give rise to spurious oscillations (Gresho et al., 1980). In the flow domains that are not considered to be long enough to impose developed flow conditions, stress-free conditions at the domain outlet may be used. In this case, both shear and normal components of the surface forces at the exit are set to zero. This is again satisfied by setting of the boundary integral along the exit line to zero.  [c.97]

Of the large number of readily available gases, the proportion that turn out to be suitable for surface area determination is quite small, because a number of conditions have to be met. In the first place it is necessary that the isotherm of the adsorptive on a wide range of adsorbents shall have the characteristics described in the previous Section, 2.8 the isotherm must have a sharp knee and a well defined Point B. A number of requirements of a practical kind must also be satisfied the adsorptive must be chemically inert towards the solid the saturation vapour pressure, p , at the working temperature must be large enough to allow the accurate measurement of the relative pressure over a reasonably wide range ( 0O01 < p/p < 0-5) but, for reasons of experimental convenience, p should not exceed 1 to 2 atmospheres. In addition, the working temperatures tend to be limited to those which can be obtained with the common refrigerants, notably nitrogen (b.p. 77 K), oxygen (b.p. 90 K), carbon dioxide slush (195 K), melting ice (273 K), along with the range, l53 to 323 K, which can be conveniently attained by an adjustable thermostat bath. Finally, it is desirable that the shape of the adsorbate molecule shall not be far removed from spherical symmetry, so as to minimize the uncertainty in a arising from the different possible orientations on the surface.  [c.73]

Air heated by steam heat exchangers or direct flame is blown through the dryers and moves the fibers in suspension as they dry and pass through the dryer. Temperatures are in the 120—150°C range at the inlet to the dryer and about 70°C at the dryer exit. Fiber moisture should be in the 6—12% range at this point if blowline blending is used. It must be lower if machine blending is to be used later because of water added with the adhesive resin. The resin will not cure in the dryer because of both the short residence time and the cooling effect of evaporating water in the dryer. Where there is moisture in the fiber, this drying and evaporating effect prevents the resin from becoming hot enough to cure.  [c.389]

Wet ground mica products account for approximately 15% of the total mica market. These products are produced by grinding either scrap or flake mica or both in a Muller or Chaser mill which consists of a 4.57-m diameter tub containing two 1.22-m diameter steel spiked wheels or rollers. A 1.13 t charge of mica is placed in the tub along with enough water to represent 25—35% of the batch. The necessary water content for good delamination and grinding varies for micas from different deposits. After charging the mill, rollers rotate at 30 rpm through the mica pulp for six to eight hours to cause the mica flakes to sHde across each other, and thereby cause delamination by friction while producing a grinding action that reduces particle si2e.  [c.289]

Mean Field Approximations. The two cases outlined above may be regarded as the extreme limits of polymer—polymer interactions. There is an important intermediate situation for somewhat polar polymer pairs where equation 6 is not vaUd, but the interactions are far from specific enough to be regarded in quasichemical terms. These cases may lead to exothermic interactions as clearly illustrated by the following well-known examples poly(phenylene oxide)—polystyrene (PPO—PS) (76) tetramethyl bisphenol polycarbonate—PS (9) bisphenol A polycarbonate—polyesters (43,54,108,109) PS—poly(vinyl methyl ether) (PVME) (110) etc. As of this writing (ca 1995), there is no method for predicting a priori the interaction energies for such systems. However, patterns emerge from the Hterature which can help to guide the selection of pairs that are likely to be miscible. Eor example. Table 1 summarizes a variety of observations (111) that suggest a high incidence of miscibility of polymers containing halogen units with members of three families of polymers with ester units in their chains or pendent groups other examples of this kind also exist (112,113). Some authors suggest that systems like those in Table 1 involve hydrogen bonding, via hydrogen atoms that are either a or P to the halogen (1,75). Small shifts in the infrared carbonyl bands  [c.411]

Stabilization of the T conformation under normal conditions is illustrated by the reaction of 2,3-diphosphoglycerate, (2,3-DPG) (Fig. 2). The negative charges on this polyphosphate form electrostatic, reversible interactions with eight positive charges on hemoglobin two a-amino groups of valine NAI(I)p, two S-amino groups of lysine EF6(82)p, and four histidines, NA2(2)p and HC3(I43)p. In the R state the dimensions of the pocket change enough so that 2,3-DPG does not fit as well, and it drops out. Thus 2,3-DPG preferentially stabilizes the Tconformation and has an overall effect of reducing oxygen affinity and increasing cooperativity. Analogues of 2,3-DPG, used to modify hemoglobin by forming permanent, covalent bonds, are variously effective, depending on molecular dimensions and charge. Some of the compounds react with only one of the reactive amino groups in the 2,3-DPG pocket others react with all four.  [c.162]

Ignition. To understand the phenomenon of ignition it is necessary to consider the following concepts ignition source, gas temperature, flame volume, and presence of quench wall surfaces. In general, there are two main methods of igniting a flammable mixture. In the self-ignition method, the mixture is heated slowly so that the vapor released as the temperature is raised ignites spontaneously at a particular temperature. In the forced ignition method, a small quantity of combustible mixture is heated by an external source and the heat released during the combustion of this portion results in propagation of a dame. The external ignition source can be an electric spark, pilot dame, shock wave, etc. For ignition to take place the following conditions should be satisfied (/) the amount of energy suppHed by the ignition source should be large enough to overcome the activation energy barrier (2) the energy released in the gas volume should exceed the minimum critical energy for ignition and (J) the duration of the spark or other ignition source should be long enough to initiate dame propagation, but not too long to affect the rate of propagation. Ignition models fall into two categories the thermal model explains the ignition as resulting from supplying the mixture with the amount of heat sufficient to initiate reaction. In the chemical diffusion model the main role of the ignition source is attributed to the formation of a large number of free radicals in the preheat 2one, where their diffusion to the surrounding region initiates the combustion process. The thermal model is appHed more widely in the Hterature and shows better agreement with experimental data.  [c.515]

The most difficult shades to produce level are pale shades, and the most difficult time ia the process to obtain level dyeiag is duriag the early stages of dyeiag whea the number of poteatial sites of attractioa greatly exceeds the number of dyestuff molecules. Reduciag the sites available is achieved by altering pH, electrolyte, etc. Ia practical dyeiag situatioas the early stages of dyeiag are always carried out uader coaditioas that promote level dyeiag, ie, slow dyeiag rates and working close to relative saturation. Once there is enough dye absorbed ia a level manner to dictate that the remainder will dye ia a level fashioa thea it is possible to change the conditions to iacrease the rate of dyeiag. This is doae ia order to obtaia commercially acceptable rates of dyebath exhaustioa. The definition of appHcatioa processes and classification of dyes is determined by the need for this control and how it can be achieved.  [c.353]

An attempt has been made to bring together most of the methods currently available for project evaluation and to present them in such a way as to make the methods amenable to modern computational techniques. To this end the practices of accountants and others have been reduced, where possible, to mathematical equations which are usually solvable with an electronic hand calculator equipped with scientific function keys. To make the equations smtable for use on high-speed computers an attempt has been made to devise a nomenclature vmich is suitable for machines using ALGOL, COBOL, or FORTRAN compilers. The number of letters and numbers used to define a variable has usually been limited to five. The letters are mnemonic in Enghsh wherever possible and are derived in two ways. First, when a standard accountancy phrase exists for a term, this has been abbreviated in capital letters and enclosed in parentheses, e.g., (ATR), for assets-to-turnover ratio (DCFRR), for discounted-cash-flow rate of return. Clearly, the parentheses are omitted when the letter group is used to define the variable name for the computer. Second, a general symbol is defined for a type of variable and is modified by a mnemonic subscript, e.g., an annual cash quantity Afc, annual total capital outlay, /year. Clearly, the symbols are written on one line when the letter group is used to define a variable name for the computer. In other cases, when well-known standard symbols exist, they have been  [c.803]

The pieces of random-dumped packing should be no larger than one-eighth of the tower diameter to minimize the wall effect which gives larger voids at the wall. The packing support can be an open grid or multiarch support if the dispersed phase is distributed to the top of the bed. But the packing support may also be a sieve plate with multiple light-liquid risers if the heavy phase is to be redispersed onto a lower bed. Or the packing support may be a sieve plate with multiple heavy-phase downcomers if the light phase is to be dispersed up into the bed. The streams of dispersed phase should be far enough apart to avoid coalescence at the dispersion plate, and the dispersed phase should not preferentially wet the packing. If the droplets wet the packing, they will coalesce and stream along the packing as rivulets. Eckert [Hydrocarbon Proce.ss., 117 (March 1976)] recommends the use of packed towers when the interfacial tension is below 10 mN/m (dyn/cm).  [c.1476]

Sterilization by Filtration Air is almost always sterilized by filtration. The alternative of heating to sterilize has been successfm for small installations, but large equipment for heating an air stream to sterihzing temperatures has not been sufficiently rehable. While it seems simple enough to maintain a section of the air-supply pipeline at high temperature, automatic control is needed to adjust for varying heat transfer as flow rate changes, and an air cooling section is needed to prevent excessive heat load on the fermenter. Furthermore, energy costs are now much higher than when heating seemed a promising alternative to filtration. For exit gases from a fermentation that has hazardous organisms, heating is a reasonable precaution, and cost is not the key factor. A clever heating method failed in full-scale testing. The air was compressed to raise its temperature by the Joiile-Thompson effec t, out the method was abandoned because several batches became contaminated. Any flow system for heat sterilization is crippled by process upsets because a slug of material can have inadequate temperature or exposure time for filling.  [c.2141]

During a high-frequency (FOW) surge, the inductive impedance of the windings becomes very high and offers an open circuit to the arriving surge, and there is no inductive transference of voltage surges to the secondary. But at lower frequencies, such as during overvoltages, long-duration switching surges (250/2500 /J.s). and even during lightning surges, the windings acquire enough inductive continuity to transfer a part of these voltages to the secondary, depending upon theyj, of the arriving surge, in the ratio of their transformation (V2/V,), It is generally noticed that such transferences hardly exceed the power frequency withstand level of the windings and are thus less critical. Nevertheless they must be counter-checked while designing the surge protection scheme for the whole system. If it is higher, then  [c.601]

When visualizing a combustion process, it is useful to think of it in terms of the three Ts time, temperature, and turbulence. Time for combushon to occur is necessary. A combustion process that is just initiated, and suddenly has its reactants discharged to a chilled environment, will not go to completion and will emit excessive pollutants. A high enough temperature must exist for the combustion reaction to be initiated. Combushon is an exothermic reachon (it gives off heat), but it also requires energy to be inihated. This is iUustrated in Fig. 6-5.  [c.79]

Onee the rotor system has been installed, downtime is the key eost asso-eiated with vibration. For example, it is not unusual for lost produetion eosts to be measured in tens of thousands of dollars per day for a ehemieal plant eompressor. Obviously, shutting down the maehine to rebalanee the rotor is a deeision not taken lightly. The optimum approaeh is to determine eorreetions while the maehine is running, and shutdown only long enough to install the trim balanee weights. The multiplane balaneing proeedure permits  [c.598]

This approach will provide a number aecurate enough for initial planning. For detailed design, the proeess engineer should work elosely with the meehanieal engineer and/or vendor representative involved to set exact requirements, ineluding orifice type and size for the minimum flow line. Also, a eooler may be required in the minimum flow line or it may need to be routed to a vessel. For boiler feedwater pumps, a special stepped type orifice is often used to eontrol flashing.  [c.106]

Attempts to construct a model of this molecule will show that the geometry of the bicyclic system does not permit coplanarity of tiie atoms bound to the sfp carbons. As a result of the strain, the molecule has, at most, transitory existence.The absence of such bridgehead double bonds was noted long ago and formulated as Bredt s rule. As the structural basis for Bredt s rule became clear, it was evident that the prohibition against bridgehead double bonds would not be absolute. When the bridges of tiie bicyclic system are large enough to permit planarity of the double bond, bridgehead alkenes are capable of existence. It has been proposed that the limit for unstable but isolable bridgehead alkenes is reached when the largest ring containing the double bond is at least eight-membered. Bridgehead alkenes in which the largest ring is seven-membered are expected to be cspable only of short existence. These proposals have subsequently been tested and verified by the development of successful synthesis of bridgehead alkenes, such as those shown in Scheme 3.3." The strained double bonds in these molecules are exceptionally reactive and undergo a variety of addition reactions. The total strain in the bridgehead alkenes can be computed by molecular mechanics methods. Some of the calculated strain energies are included in Scheme 3.3. The total strain energy can be dissected to indicate that fiaction of tiie total strain which is due to the twist of the carbon-carbon double bond. This strain proves to be a quite reliable predictor of the stability of bridgehead alkenes.  [c.166]


See pages that mention the term Exhaust wall jet-enhanced : [c.33]    [c.2488]    [c.301]    [c.352]    [c.309]    [c.411]    [c.1229]    [c.1605]    [c.2526]    [c.685]    [c.467]    [c.38]   
Industrial ventilation design guidebook (2001) -- [ c.978 , c.979 , c.980 , c.981 , c.982 , c.983 ]