Factors Influencing Thermal Efficiency

Increase in thermal efficiency with the core outlet temperature is shown in Fig. 3.11. The thermal efficiency is about 41% in the Super LWR plant with the core outlet temperature of 400°C. It is about 45% when the core outlet temperature is 566°C, the same outlet temperature as the supercritical FPP. The present design criteria require the outlet temperature be higher than 500°C, which corresponds to a thermal efficiency higher than 43.8%. 

At the same time, the ratio of extracted steam flow rate from the moisture separator to the fourth HP feedwater heater (S 4 in Fig. 3.9a [4]) should be greatly reduced when enhancing the core outlet temperature. As shown in Fig. 3.12c, when the core outlet temperature is set at 400 C, 8 4 is about 20% of the total flow rate, while 5x4 is nearly 0 when the core outlet temperature is raised to 600°C. Again, it should be remembered that the extraction points are decided to obtain the highest thermal efficiency. 

As shown in Fig. 3.12d, the steam flow rate through the condensers increases with the core outlet temperature. 

The relationship between the overall branch steam flow rate and the core outlet temperature is shown in Fig. 3.12e. 

The feedwater temperature can be gradually decreased by removing the HP feedwater heaters [6]. When the feedwater temperature is 280 C, the BOP requires four HP and four LP low pressure feedwater heaters. When it is 210°C, the cycle has two HP and four LP feedwater heaters. There are only four LP feedwater heaters in the case of ISO C. 

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Symmetry is another factor to affect Tm. The salts with symmetric ions generally show higher Tm than those with asymmetric ones. For example, 1,3-dimethylimidazolium tetrafluoroborate showed higher Tm than 1-methylimi-dazolium or l-ethyl-3-methylimidazolium salts, as shown in Figure 3.1. In the case of tetraalkylammonium salts, their Tm also increased with increasing symmetry of the cation structure [18]. This tendency is understood to relate to the structural effect on crystallinity [19], i.e., highly symmetric ions are more efficiently packed into the crystalline structure than unsymmetric ones. Other kinds of chain structures such as polyether [20], perfluorocarbon [21], etc. [22] are obviously also effective in influencing thermal properties. 

Considerations of steam cycle efficiency and cost of the pressure circuit influence selection of coolant pressure. Heat transfer performance has not been a contributory factor in determination of pressure as there is no significant change in performance over the range of Interest. Higher thermal efficiency leads to a requirement for higher coolant pressure which increases the pressure circuit cost, largely due to the influence of the zlrcaloy pressure tubes. In addition to capital cost, fuel cost is also affected because of neutron absorption by the thicker pressure tube. Circuit pressure is therefore selected to obtain the optimum balance between these factors. 

Wang et al. [96] reported a decrease of char residue by increasing the amount of OMMT in addition-type sihcone rubber composites, whereas the initial and center temperatures of thermal degradation of these samples showed first an increase followed by decrease. Similar behavior was reported for hydroxyl-containing (condensation type) sihcone rubber composites, that are known to vulcanize via dehydration of the hydroxyl end groups [97]. It was concluded that there are two factors influencing the thermal stability of composites (i) the incorporation of efficiently dispersed OMMT, that can prevent heat transport and thus improve the thermal stability of composites, and (ii) the OMMT contains some molecules that are able to evolve even at low temperatures and, some of them, would certainly impair the thermal stability of composites. 

Efficiency Total system thermal efficiency is influenced by many factors including... 

The factors affecting the gas turbine thermal efficiency and specific output (specific output = output per kg/s of gas flowing through the engine) can be divided into two groups— thermodjuiamic factors and the influence of ambient conditions. 

The compressor pressure ratio and the turbine inlet temperature have a great influence on the unit thermal efficiency and the specific output. Further, those two factors interact in such a way that a certain pressure ratio is optimum for a certain turbine inlet temperature. See Figs. T-48 and T-49. 

The decoupling efficiency depends on two factors [Engl, Mehl] (1) The amplitude (Oil = - y fii/ of the decoupling field in comparison with the strength of the heteronuclear dipole-dipole interaction. (2) The modulation of the heteronuclear dipole-dipole coupling by flip-flop transitions in the system of the abundant / spins, which communicate by the homonuclear dipole-dipole interaction. In addition to this, the influence of thermal motion has to be considered [Mehl]. 

Oxley et al.[53, 54] have shown that the thermal stability of AN is significantly influenced by the type of additives used in mixtures with AN. For example, basic additives such as carbonate, formate, oxalate, and mono-phosphate salts significantly raise the temperature of the AN exotherm and enhance AN stability. However, stability seems to be increased even in the absence of an increase in pH of the AN solution, as is the case for urea additives which upon decomposition form ammonia which only then increases the basisity of the medium.[54] As the most efficient stabilizers were found to contain carbon, it was speculated that formation of carbon dioxide may be an important factor in the ability of a compound to... 

Some characteristics of initiators used for thermal initiation arc summarized in Table 3.1. These provide some general guidelines for initiator selection. In general, initiators which afford carbon-ccntcrcd radicals e.g. dialkyldiazcncs, aliphatic diacyl peroxides) have lower efficiencies for initiation of polymerization than those that produce oxygen-centered radicals. Exact values of efficiency depend on the particular initiators, monomers, and reaction conditions. Further details of initiator chemistry are summarized in Sections 3.3.1 (azo-compounds) and 3.3.2 (peroxides) as indicated in Table 3,1. In these sections, we detail the factors which influence the rate of decomposition i.e. initiator structure, solvent, complexing agents), the nature of the radicals formed, the susceptibility of the initiator to induced decomposition, and the importance of transfer to initiator and other side reactions of the initiator or initiation system. The reactions of radicals produced from the initiator arc given detailed treatment in Section 3.4. 

The efficiency and randomness of the incorporation of a second monomer depend on the copolymerization parameters (see Section 3.1) and the type of chain growth method applied. For each monomer pair these factors have to be evaluated and considered for defining stmcture and functionality. In addition, basic polymer properties like solubility and thermal properties defined by the major monomer are strongly influenced by a second monomer of different functionality thus, in any random copolymerization process, it is usually not possible to introduce a second functionality without compromising the properties of the parent homopolymer, and this is enhanced with increasing the comonomer ratio. 

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