Semi-closure

Most of the novel cycles considered later in this chapter involve semi-closure , i.e. recirculation of some part of the exhaust gases into the compressor as indicated in the simplest example shown in Fig. 8.3. In effect, the exhaust products stream becomes an oxygen carrier. 

we first discuss whether such semi-closure (which is introduced so that CO2 separation can be undertaken more easily) is likely to lead to higher or lower thermal efficiency, and in this discussion it is helpful to consider recirculation in relation to an air standard cycle (see Fig. 8.4). Fig. 8.4a shows a closed air standard cycle with unit air flow Fig. 8.4b shows an open cycle similarly with unit air flow and an air heater rather than a combustion chamber. The cycles are identical in every respect except that in the former the turbine exhaust air from the turbine is cooled before it re-enters the compressor. In the latter, the turbine exhaust air is discharged to atmosphere and a fresh charge of air is taken in by the compressor. The quantities of heat supplied and the work output are the same for each of the two cycles, so that the thermal efficiencies are identical. 

We can then add the two cycles together as shown in Fig. 8.4c, to form a semi-closed plant. There is double the flow through this new plant, double the heat supply and double the work output. Strictly, the total heat rejected is not doubled half the turbine exhaust is now discharged to the atmosphere and half the heat rejected into a cooler before it is recirculated into the compressor. The thermal efficiency of this double semi-closed plant is unchanged from that of the original closed cycle and the original open cycle. So there is apparently no thermodynamic advantage in semi-closure it is undertaken for a different purpose. 

A similar argument can be used for a fuelled semi-closed cycle, assuming that it can be regarded as the addition of an open CBT plant and a closed CHT cycle with identical working gas mass flow rates (and small fuel air ratios). Suppose the latter receives its heat supply from the combustion chamber of the former in which the open cycle combustion takes place. If the specific heats of air and products are little different, then the work output is doubled when the two plants are added together, but the fuel supply is also approximately doubled. The efficiency of the combined semi-closed plant is, therefore, approximately the same as that of the original open cycle plant. 

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A number of plants have been proposed in which pure oxygen is used for combustion, usually in combination with the concept of cycle semi-closure. 

The mechanism of the cycloaddition reaction of benzaldehyde 2a with Danishefsky s diene 3a catalyzed by aluminum complexes has been investigated theoretically using semi-empirical calculations [14]. It was found that the reaction proceeds as a step-wise cycloaddition reaction with the first step being a nucleophilic-like attack of Danishefsky s diene 2a on the coordinated carbonyl compound leading to an aldol-like intermediate which is stabilized by interaction of the cation with the oxygen atom of the Lewis acid. The next step is the ring-closure step, giving the cycloaddition product. 

Closure liners of pulpboard or cork, unless specially treated with a preservative, foil or wax coating, are often a source of mould contamination for liquid or semi-solid products. A closure with a plastic flowed-in linear is less prone to introduce or support microbial growth than one stuck in with an adhesive, particularly if the latter is based on a natural product such as casein. If required, closures can be sterilized by either formaldehyde or ethylene oxide gas. 

Make a preliminary mechanical design for the vertical thermosyphon reboiler for which the thermal design was done as Example 12.9 in Chapter 12. The inlet liquid nozzle and the steam connections will be 50 mm inside diameter. Flat plate end closures will be used on both headers. The reboiler will be hung from four bracket supports, positioned 0.5 m down from the top tube plate. The shell and tubes will be of semi-killed carbon steel. 

Primary container-closure system-related data will need to cover storage, transportation, and use. The choice of materials of construction, their description, and the ability of the container-closure system to protect from moisture and/or light will need to be considered. The compatibility of the container-closure and its contents will need to consider sorption, leaching, and safety. The performance of the container-closure system will also need to be considered in terms of dose delivery from any associated device that is to be supplied as part of the product. Container-closure components will require adequate specifications covering description, identification, critical dimensional tolerances, and test methodology (including pharma-copeial and noncompendial methods). More data are likely to be required for liquid or semi-liquid products than for solid dosage forms. In the latter, product stability data and container-closure system specifications may suffice. 

Hakonson, T.E., Capping as an alternative for land fill closures-perspectives and approaches, Environmental Science and Research Foundation, Proceedings, Landfill Capping in the Semi-Arid West Problems, Perspectives, and Solutions, Grand Teton National Park, WY, ESRF-019, May 21-22, 1997, pp. 1-18. 

Comment After approximately 72 hours with little sleep, Burns is now intermittently in contact with his surroundings. He will spend much of the next 24 hours alternating between periods of sleep and semi-oriented wakefulness. Some episodes of delirium will continue, followed by a rapid return of awareness and improvement on his Number Facility and Speed of Closure scores, as well as his ability to conceptualize and draw a normal picture of a man. Incapacitation was longer in this case than in most, by at least 24 hours. A graphical illustration of his time course appears at the end of this chapter. 

The first synthesis of a semibuckminsterfullerene was accomplished by a procedure analogous to the preparation of corannulene except that 1,2,5,6-tetrake-topyracene served as the starting material (Scheme 5). Flash vacuum pyrolysis of the tetrachloro compound led to a remarkable quadruple ring closure to produce the semi-buckminsterfullerene 27. The NMR shows three methine carbons and five quaternary carbons at 125.5, 126.8, 127.3, 128.6, 136.7, 137.3, 142.0, and 145.4 ppm. The latter signals compare favorably to the single resonance observed at 143 ppm for buckminsterfullerene. 

Although direct numerical simulations under limited circumstances have been carried out to determine (unaveraged) fluctuating velocity fields, in general the solution of the equations of motion for turbulent flow is based on the time-averaged equations. This requires semi-empirical models to express the Reynolds stresses in terms of time-averaged velocities. This is the closure problem of turbulence. In all but the simplest geometries, numerical methods are required. 

To explain the enantioselectivity obtained with semi-stabilized ylides (e.g., benzyl-substituted ylides), the same factors as for the epoxidation reactions discussed earlier should be considered (see Section 10.2.1.10). The enantioselectivity is controlled in the initial, non-reversible, betaine formation step. As before, controlling which lone pair reacts with the metallocarbene and which conformer of the ylide forms are the first two requirements. The transition state for antibetaine formation arises via a head-on or cisoid approach and, as in epoxidation, face selectivity is well controlled. The syn-betaine is predicted to be formed via a head-to-tail or transoid approach in which Coulombic interactions play no part. Enantioselectivity in cis-aziridine formation was more varied. Formation of the minor enantiomer in both cases is attributed to a lack of complete control of the conformation of the ylide rather than to poor facial control for imine approach. For stabilized ylides (e.g., ester-stabilized ylides), the enantioselectivity is controlled in the ring-closure step and moderate enantioselectivities have been achieved thus far. Due to differences in the stereocontrolling step for different types of ylides, it is likely that different sulfides will need to be designed to achieve high stereocontrol for the different types of ylides. 

A semi-classical estimate is obtained by dropping the excitation energy of one of the systems in the denominator in Eq. (3-11), assuming instantaneous instead of frequency-dependent interaction. Then, by means of the closure relation, it is easy to show that in the dipole approximation Eq. (3-11) transforms into [3,38]... 

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