LT maintenance maintenance


Dissolve 50 g. of benzoic acid in 230 ml. of concentrated sulphuric acid in a litre flask fitted with a ground-glass reflux water-condenser. (Rubber or cork must not be used.) Now add a few ml. of the fuming nitric acid down the condenser, shake the flask well and keep it cool by immersion in ice-water, Continue the intermittent addition of nitric acid (about 10 ml. at a time) with continuous shaking and cooling a great deal of heat is evolved on each addition and a clear yellow solution is obtained. When the addition is complete, add a few pieces of unglazed porcelain and transfer the flask to a cold water-bath. Raise the temperature of the latter gradually during 45 minutes to 100 . [At 70-80 the reaction sometimes tends to become vigorous, and should then be moderated by careful immersion in cold water.] Maintain the mixture at 100° for 15 minutes, with occasional shaking, and then transfer the flask to an oil-bath at 100°. Raise the temperature gradually to 130 during 30 minutes and then maintain it between 130" and 140 for i hour. Thus the total period of heating Is 2 hours during w hich the temperature is gradually raised to 140 . Now cool the flask crystals of 3,5-dinitrobenzoic acid begin to separate at about 90 . When cold pour the contents of the flask in 3-4 1. of ice-water. Filter oflF the crystals on a Buchner funnel and wash with water. After drying, the crystals have m.p. 204 (yield, 49 g.) and are sufficiently pure for the preparation of 3,5-dinitrobenzoyl chloride (see below).  [c.242]

A charge of —e circulating in an orbit is equivalent to a current flowing in a wire and therefore causes a magnetic moment. That due to orbital motion, is a vector which is opposed to the corresponding orbital angular momentum vector I, as shown in Figure 7.2(a). The classical picture of an electron spinning on its own axis indicates that there is a magnetic moment associated with this angular momentum also. Figure 7.2(a) shows that this vector is opposed to s. The magnetic moments and can be regarded as acting rather like tiny bar magnets. For each electron they may be parallel, as in Figure 7.2(a), or opposed, as in Figure 7.2(b).  [c.204]

Each of the three time-averaged momentum equations contains three unknown turbulent stresses, pu[u j, commonly termed Reynolds stresses, only six of which are independent. The Reynolds stress pu[ for example, is the rate at which x-momentum, pu[, is being transported in the jy-direction by the velocity fluctuation u 2. A hierarchy of equations for velocity correlation functions, ie, averages of products of ti-, can be obtained, but each equation so derived involves an unknown higher order correlation function and hence the set of equations is not closed. A turbulence model is needed to determine the turbulent transport terms before the set of equations can be solved. Turbulence modeling is concerned with the development and testing of closure assumptions for the Reynolds stresses. A large number of closure models are available. They are usually divided into two groups, eddy viscosity models and Reynolds stress models, according to whether or not the Boussinesq assumption is appHed.  [c.102]

To illustrate the use of the momentum balance, consider the situation shown in Figure 21c in which the control volume is bounded by the pipe wall and the cross sections 1 and 2. The forces acting on the fluid in the x-direction are the pressure forces acting on cross sections 1 and 2, the shear forces acting along the walls, and the body force arising from gravity. The overall momentum balance is  [c.108]

Typically, seawater enters the solar pond system and moves successively from one pond to the next. Operators control the quantity of flow with mechanical gates to maintain target brine densities and pond levels. Iron, calcium, and magnesium carbonates crystallize when the concentration of brine is 3.5—13°Bh. About 85% of the calcium sulfate crystallizes as gypsum and then anhydrite at brine concentrations from 13—25.4°Bh. Solar salt production is a form of fractional crystallization. Brine reaching the crystallizers contains in solution calcium sulfate, magnesium sulfate, magnesium chloride, and small amounts of potassium chloride, plus minuscule amounts of other elements. The saturated brine at a specific gravity of 25.4°Bh is fed onto level, rectangular crystallizing ponds to maintain a brine depth of 30 cm or less. As evaporation proceeds, sodium chloride precipitates and forms a salt layer 10—25 cm thick. In many solar salt faciUties, the first crop of salt deposited remains on the crystallizer bottoms as salt floors to prevent contamination from soil and to increase the strength of the crystallizer bottoms to support harvesting equipment. When the brine reaches 25—30°Bh, the bittern is discharged. Most of the magnesium sulfate and magnesium and potassium chlorides remains in the bittern.  [c.183]

The energy of a backscattered particle detected at a given angle depends upon two processes the loss of energy by the particle due to the transfer of momentum to the target atom during the backscattering event, and the loss of energy by the particle during transmission through the sample material (both before and after scattering). Figure 1 is a schematic showing backscattering events occurring at the surface of a sample and at a given depth in the sample. For scattering at the sample s surface the only energy loss is due to momentum transfer to the target atom. The ratio of the projectile s energy after a collision to the its energy before a collision Ei/Ef is defined as the kinematic factor  [c.477]

The somewhat controversial theory of risk homeostasis is relevant to a discussion of risk taking. RHT was developed initially in the area of driving behavior (Wilde, 1984). The theory states that accident rates are not determined by actual levels of intrinsic risk but by the levels of risk acceptable to individuals in the situation. The theory implies that people adjust their risk-taking behavior to maintain a constant level of perceived risk. Thus, if improved safety measures are introduced (e.g., better guarding, improved protection systems then individuals will behave in a more risky fashion in order to maintain their accustomed levels of risk.  [c.138]

If one just concentrates on the radioactive material in SNF, the volume is very small, especially compared to waste from other power production practices. However, one can only discuss the separated radioactive material if it has undergone extensive reprocessing. If SNF is to be isolated, as in a place such as Yucca Mountain, with perhaps 70 miles of tunnels, the volume is that of the interior of this minor mountain. Isolation of up to 100,000 metric tons of SNF in Yucca Mountain means that for the United States, approximately all the SNF made to date and that expected in the operating lifetime of all current reactors can be put there. Approximately 2,000 metric tons of SNF are produced each year in the United States. Waste volume and placement depend on the amount of compaction and consolidation at the sites. The plans for the Yucca Mountain present a realistic and understandable picture of the volume of SNF.  [c.884]

Conservation of Momentum. If the mass of a body or system of bodies remains constant, then Newton s second law can be interpreted as a balance between force and the time rate of change of momentum, momentum being a vector quantity defined as the product of the velocity of a body and its mass.  [c.164]

Large values of the uncertainty are assigned to the generated points, because the primary purpose of the generated points is not to have them fit accurately, but rather to maintain a reasonable slope of the function in the range outside the experimental points.  [c.140]

More often than not, solid-catalyzed reactions are multiple reactions. For reactions in parallel, the key to high selectivity is to maintain the appropriate high or low concentration levels of reactants at the catalyst surface, to encourage the desired reaction, and to discourage the byproduct reactions. For reactions in series, the key is to avoid the mixing of fluids of different compositions. These arguments for the gross flow pattern of fluid through any reactor have already been developed.  [c.47]

However, the laboratory data seem to indicate that a constant concentration in the reactor to maintain 63 percent sulfuric acid would be beneficial. Careful temperature control is also important. These two factors would suggest that a continuous well-mixed reactor is appropriate. There is a conflict. How can a well-defined residence time be maintained and simultaneously a constant concentration of sulfuric acid be maintained  [c.52]

An additional separator is now required (Fig. 4.2a). Again, the unreacted FEED is normally recycled, but the BYPRODUCT must be removed to maintain the overall material balance. An additional complication now arises with two separators because the separation sequence can be changed (see Fig. 4.26). We shall consider separation sequencing in detail in the next chapter.  [c.96]

Example 6.2 A process is to be divided into two operationally independent areas of integrity, area A and area B. The stream data for the two areas are given in Table 6.6." Calculate the penalty in utility consumption to maintain the two areas of integrity for = 20°C.  [c.182]

Find a way to overcome the constraint while still maintaining the areas. This is often possible by using indirect heat transfer between the two areas. The simplest option is via the existing utility system. For example, rather than have a direct match between two streams, one can perhaps generate steam to be fed into the steam mains and the other use steam from the same mains. The utility system then acts as a buffer between the two areas. Another possibility might be to use a heat transfer medium such as a hot oil which circulates between the two streams being matched. To maintain operational independence, a standby heater and cooler supplied by utilities is needed in the hot oil circuit such that if either area is not operational, utilities could substitute heat recovery for short periods.  [c.184]

Figure 6.25a shows the same grand composite curve with two levels of saturated steam used as a hot utility. The steam system in Fig. 6.25a shows the low-pressure steam being desuperheated by injection of boiler feedwater after pressure reduction to maintain saturated conditions. Figure 6.256 shows again the same grand composite curve but with hot oil used as a hot utility.  [c.186]

Solution First, we must construct the balanced composite curves using the complete set of data from Table 7.1. Figure 7.5 shows the balanced composite curves. Note that the steam has been incorporated within the construction of the hot composite curve to maintain the monotonic nature of composite curves. The same is true of the cooling water in the cold composite curve. Figure 7.5 also shows the curves divided into enthalpy intervals where there is either a  [c.220]

Consider changing from batch to continuous operation. Batch processes, by their very nature, are always at unsteady state and thus are difficult to maintain at optimal conditions.  [c.290]

Consider die following intuitive scheme, in which the timing between a pair of pulses is used to control the identity of products [ ]. The scheme is based on the close correspondence between the centre of a wavepacket in time and that of a classical trajectory (Elirenfest s theorem). The first pulse produces an excited electronic state wavepacket. The time delay between the pulses controls the time that the wavepacket evolves on the excited electronic state. The second pulse stimulates emission. By the Franck-Condon principle, the second step prepares a wavepacket on the ground electronic state with the same position and momentum, instantaneously, as the excited-state wavepacket. By controlling the position and momentum of the wavepacket produced on the ground state through the second step, one can gain some measure of control over product fonnation on the ground state. This pump-dump scheme is illustrated classically in figure Al.6.27. The trajectory originates at the ground-state surface minimum (the equilibrium geometry). At t = 0 it is promoted to the excited-state potential surface (a two-dimensional hamionic oscillator in this model) where it originates at the Condon point, that is, vertically above the ground-state minimum. Since this position is displaced from equilibrium on the excited state, the trajectory begins to evolve, executing a two-dimensional Lissajous motion. After some time delay, the trajectory is brought down vertically to the ground state (keeping both the instantaneous position and momentum it had on the excited state) and allowed to continue to evolve on the ground-state, figure Al.6.27 shows that for one choice of time delay it will exit mto chaimel 1, for a second choice of time delay it will exit into channel 2. Note how the position and momentum of the trajectory on the ground state, innnediately after it comes down from the excited state, are both consistent with the values it had when it left the excited state, and at the same time are ideally suited for exiting out their respective chaimels.  [c.270]

Coherent states and diverse semiclassical approximations to molecular wavepackets are essentially dependent on the relative phases between the wave components. Due to the need to keep this chapter to a reasonable size, we can mention here only a sample of original works (e.g., [202-205]) and some summaries [206-208]. In these, the reader will come across the Maslov index [209], which we pause to mention here, since it links up in a natural way to the modulus-phase relations described in Section III and with the phase-fiacing method in Section IV. The Maslov index relates to the phase acquired when the semiclassical wave function haverses a zero (or a singularity, if there be one) and it (and, particularly, its sign) is the consequence of the analytic behavior of the wave function in the complex time plane.  [c.108]

The second most important source of short-term financing is notes payable from commercial banks. Banks normally reqmre a Borrower to maintain a compensating balance. For example, if a company requires a loan of 100,000, it must borrow more than this, say, 120,000 (on which it pays interest), in order to maintain a minimum checldng-accouut balance of 20,000. Commercial banks also provide a wide variety of other services that can be of great help to companies in temporary financial difficulties.  [c.852]

The energy E of the levels is more conveniently represented on a momentum scale. The sequence of levels at the left vertical axis corresponds to the infinitely deep well without the central barrier. The presence of the barrier primarily affects energy levels with low angular momentum because only these have a high probability density near the center of the well. Also drawn in Fig. 14 is the zigzagging path of the highest occupied level of a C o Cs, cluster taking on various values of Rc,j /Rqm as it grows from x = 1 to x = 500. To determine this path, we used Rq = 4 A and the Cs-density bulk value of 0.009 atoms per A . The (sub-)shells resulting from this path are listed in Table 1. Obviously, the agreement with the experimentally observed shell closings has not been improved by including C40 as an impenetrable barrier at the center of the metal cluster. Varying Rcff, and the Cs-density within reasonable bounds does not significantly improve the situation. On the other hand, this simple model shows that the shell structure of a metal sphere does not  [c.179]

Stirred tanks are the most eommon form of erystallizers. Nevertheless, due to high loeal gradients of the energy dissipation, the fluid dynamies are not well understood and depend to a large extent on the geometry of the vessel. Different forms of impellers, baffles and draft tubes ean produee very different flow fields. As a stirred tank eontains a moving impeller, the fluid eells surrounding the impeller are modelled as rotating bloeks in CFD (Bakker etai, 1997). A sliding mesh teehnique has been developed to aeeount for the movement of the rotating impeller grid relative to the surrounding motionless tank eells. Xu and MeGrath (1996) eompared the sliding mesh simulation results for a stirred tank with experimental laser doppler anemometry (LDA) data and found that the data eorresponded very well. An alternative to the sliding mesh teehnique is the momentum souree model, where the impeller region is modelled as a blaek-box souree of momentum. In this ease, however, experimental data eoneerning the forees aeting on the impeller are neeessary. Furthermore, no loeal data in the impeller region ean be obtained (blaek box) when using the momentum souree model. For a sliding mesh simulation, on the other hand, no experimental data are neeessary and the flow field in the vieinity of the impeller is readily obtained.  [c.48]

Let us consider systems which consist of a mixture of spherical atoms and rigid rotators, i.e., linear N2 molecules and spherical Ar atoms. We denote the position (in D dimensions) and momentum of the (point) particles i with mass m (modeling an Ar atom) by r, and p, and the center-of-mass position and momentum of the linear molecule / with mass M and moment of inertia I (modeling the N2 molecule) by R/ and P/, the normalized director of the linear molecule by n/, and the angular momentum by L/.  [c.92]

Montan-, mountain mining montanic, montan, -alkohol, m. montanic alcohol, -Industrie, /. mining industry, -skure, /. montanic acid, -wachs, n. montan wax.  [c.304]

During these past few decades, the bicycle itself has vastly improved. The bicycles of the early 1970s usually had mechanical idiosyncrasies. Competition among manufacturers, led by the Japanese companies that entered the U.S. market, resulted in vastly improved quality control. The mountain bike, first made available on a widespread basis m 1983, offered a delightful alternative that mushroomed in popularity, and a decade later, traditional road bicycles had all but disappeared from stores. The mountain bike has become most people s vehicle of choice for city riding as well as recreational trail riding.  [c.147]

How might the interaction between two discrete particles be described by a finite-information based physics Unlike classical mechanics, in which a collision redistributes the particles momentum, or quantum mechanics, which effectively distributes their probability amplitudes, finite physics presumably distributes the two particles information content. How can we make sense of the process A scatters J5, if B s momentum information is dispersed halfway across the galaxy [minsky82]. Minsky s answer is that the universe must do some careful bookkeeping,  [c.663]

Fixed-bed catalytic reactors. Tubular reactors are also used extensively for catal3dic reactions. Here the reactor is packed with particles of solid catalyst. Most designs approximate to plug-flow behavior. Figure 2.6 shows four possible arrangements for flxed-bed reactors. The first (Fig. 2.6a) is similar to a shell-and-tube exchanger in which the tubes are packed with catalyst. The second (Fig. 2.66) has the tubes constructed inside a furnace for high temperatures. The third (Fig. 2.6c) is a series of adiabatic beds with intermediate cooling or heating to maintain temperature control. The heating or cooling can be effected by internal or external exchangers. The fourth (Fig. 2.6rf) uses direct injection of a fluid to perform heat transfer. The injected fluid might typically be cold fresh feed or cooled recycled product to control the temperature rise in an exothermic reaction. This is known as cold-shot cooling. Many other arrangements are possible.  [c.55]

One common reason for imposing constraints results from areas of integrity A process is often normally designed to have logically identifiable sections or areas. An example might be reaction area and separation area of the process. These areas are kept separate for reasons such as start-up, shutdown, operational fiexibility, safety, etc. The areas are often made operationally independent through the use of intermediate storage of process materials between the areas. Such independent areas are generally described as areas of integrity and impose constraints on the ability to transfer heat. Clearly, to maintain operational indepedence, two areas cannot be dependent on each other for heating and cooling by recovery.  [c.181]

With wastewaters containing very high organic contents, the oxygen demand may be so high that it becomes very difficult and expensive to maintain aerobic conditions. In such circumstances, anaerobic processes can provide an efficient means of removing large quantities of organic material. Anaerobic processes tend to be used when BOD levels exceed lOOOmg/liter (Ikgm ). However, they are not capable of producing very high quality effluents, and further treatment is usually necessary.  [c.314]

Figure 13.5 shows a flowsheet for the manufacture of phthalic anhydride by the oxidation of o-xylene. Air and o-xylene are heated and mixed in a Venturi, where the o-xylene vaporizes. The reaction mixture enters a tubular catalytic reactor. The heat of reaction is removed from the reactor by recirculation of molten salt. The temperature control in the reactor would be diflficult to maintain by methods other than molten salt.  [c.332]

Quantitative analysis is the estimation of the amount of element or group present in a mixture or compound. This is done by various methods, in volumetric analysis a titration, in gravimetric analysis a precipitation followed by a weighing, in colorimetric analysis the estimation of a coloured species. Other quantitative methods include infra-red spectroscopy, estimation of the opalescence of a precipitate (turbidimeiry, nephelometry and fluorimetry), estimation of optical rotation, electrolytic decomposition, potentiometric, conductometric and amperometric titrations, and polaro-graphy. Organic quantitative analysis is generally carried out by physical methods or by conversion to known derivatives which can be estimated by weighing or by titration, anaplerotic sequences Ancillary routes to the catabolic cycles in organisms, which operate to maintain levels of intermediates in these cycles despite tapping off for anabolic purposes. An example is the glyoxylate cycle. Anaplerotic sequences are most obviously seen in micro-organisms where rapid biosynthesis occurs from simple carbon compounds.  [c.34]

Heisenburg uncertainty principle For small particles which possess both wave and particle. properties, it is impossible to determine accurately both the position and momentum of the particle simultaneously. Mathematically the uncertainty in the position A.v and momentum Ap are related by the equation  [c.201]


See pages that mention the term LT maintenance maintenance : [c.577]    [c.602]    [c.1109]    [c.969]    [c.65]    [c.11]    [c.315]    [c.48]    [c.125]    [c.152]    [c.197]    [c.199]    [c.207]    [c.272]    [c.282]    [c.283]    [c.288]    [c.342]   
Industrial power engineering and applications handbook (2001) -- [ c.0 ]