Closed cycles efficiency

This is the inverse of the closed cycle thermal efficiency, when and W are expressed in the same units. 

In Chapter 1, the gas turbine plant was considered briefly in relation to an ideal plant based on the Carnot cycle. From the simple analysis in Section 1.4, it was explained that the closed cycle gas turbine failed to match the Carnot plant in thermal efficiency because of... 

The objective of the gas turbine designer is to make all the proces.ses in the plant as near to reversible as possible, i.e. to reduce the irreversibilities, both internal and external, and hence to obtain higher thermal efficiency (in a closed cycle gas turbine plant) or higher overall efficiency (in an open gas turbine plant). The concepts of availability and exergy may be used to determine the location and magnitudes of the irreversibilities. 

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. 

Gas turbines can operate in open or closed cycles. In a simple cycle (also known as an open cycle), clean atmospheric air is continuously drawn into the compressor. Energy is added by the combustion of fuel with the air. Products of combustion are expanded through the turbine and exhausted to the atmosphere. In a closed cycle, the working fluid is continuously circulated through the compressor, turbine, and heat exchangers. The disadvantage of the closed cycle (also known as the indirect cycle), and the reason why there are only a few in operation, is the need for an external heating system. That is an expensive addition and lowers efficiency. 

Lithium foil is commercially available. Its surface is covered with a "native film" consisting of various lithium compounds [Li0H,Li20,Li3N, (Li20-C02) adduct, or Li2C03], These compounds are produced by the reaction of lithium with 02, H20, C02, or N2. These compounds can be detected by electron spectroscopy for chemical analysis (ESCA) [2], As mentioned below, the surface film is closely related to the cycling efficiency. 

Highly efficient brown stock washing and closed-cycle brown stock screening... 

An engine operates on the closed Brayton cycle (Fig 4.8) and has a compression ratio of 8. Helium enters the engine at 47°C and 200 kPa. The mass flow rate of helium is 1.2 kg/sec and the amount of heat addition is 1 MJ/kg. Determine the highest temperature of the cycle, the turbine power produced, the compressor power required, the back-work ratio, the rate of heat added, and the cycle efficiency. 

The combined cycle is designed to gain maximum efficiency from the primary heat source. In most cases, both cycles are used for the same purpose—usually to generate electricity. The major combined-cycle options currently under development include open-cycle gas turbines, closed-cycle turbines, fuel cells, and magnetohydrodynamics with vapor cycles. Other combined cycles include the Diesel/Rankine cycle (Boretz, J.E.,... 

Cycle efficiency High benchmark small scale capacitors close to 100%, grid scale pumped hydro 80%... 

This reaction involves three reactants and the reason that it proceeds so efficiently is that a catalyst is used. Referring to Figure 1.5.3, note that the rhodium catalyst coordinates and combines the three reactants in a closed cycle, thus breaking the statistical odds of having all three reactants collide together simultaneously. Without a catalyst the reaction proceeds only at nonsignificant rates. This is generally true of reactions where catalysts are used. More about catalysts and their functions will be described later in this text. 

The existence of further complexes with M-Ng bonds of this type was deduced on the basis of shifts in the matrix UV/visible spectrum between argon and xenon matrices without recourse either to mixed matrices or neon matrices. (The use of neon matrices should become more frequent now that more efficient closed-cycle coolers are available.) Examples include complexes, Mo(CO)sNg, W(CO)sNg , Cr(CO)3(dfepe)Ng, Mn(dmpe)2(H)Ng, and Re(dmpe)2(H)Ng , and complexes Ru(CO)2(PMe3)2Ng ,... 

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