Brayton cycle examples

On the other hand, second law analysis of a Brayton cycle (Example 5 Section 23.6.5) reveals a high exergy content of the turbine exhaust. For this reason, great improvements in gas turbine plant efficiency can be achieved by recovering exergy in the turbine outlet with either recuperation (Example 7 Section 23.6.7) or through the use of a heat recovery boiler used to supply a secondary steam cycle in a cogeneration plant (Example 6 Sechon 23.6.6). 

For actual Brayton cycles, many irreversibilities in various eomponents are present. The T s diagram of an aetual Brayton cycle is shown in Fig. 4.6. The major irreversibilities occur within the turbine and compressor. To account for these irreversibility effects, turbine efficiency and compressor efficiency must be used in computing the actual work produced or consumed. The effect of irreversibilities on the thermal efficiency of a Brayton cycle is illustrated in the following example. 

The second step is to develop several conceptual plants (e.g., cycles A, B, and C) to meet the identified need. One of the several plants is described in Example 5.14. In this example, a three-stage regenerative steam Rankine cycle and a four-stage intercool and four-stage reheat air Brayton cycle are combined to meet the need. 

The schematic and T-s diagrams of the ideal finite-time Brayton cycle are shown in Fig. 7.26 and 7.27. The cycle is an endoreversible cycle that consists of two isentropic processes and two isobaric heat-transfer processes. The cycle exchanges heat with its surroundings in the two isobaric external irreversible heat-transfer processes. By taking into account the rates of heat transfer associated with the cycle, the upper bound of the power output of the cycle can be found as illustrated in Example 7.17. 

BRAYTON CYCLE (also referred to as the Joule Cycle) - A rotating machine in which compression and expansion take place. Gas turbine are such an example. 

As in fhe case of a turbine, rjj is generally higher than t] because the additional work supplied raises the exergy of the exit stream. It is possible to recover this exergy in later processes. For example in a Brayton cycle plant, efficiency less than unity results in a higher compressor exit temperature and enthalpy, which reduces the heat requirements of the combustion chamber. 

Analysis procedures for Brayton cycles are similar to the previous examples of Rankine cycles with the exception that properties are determined from gas fables. The gas turbine in Figure 23.21 is analyzed using air standard assumptions, which consider the working fluid to be air and treat combustion as a heat addition process. A more accurate analysis could employ tables that account for combustion products, such as Keenan and Kay (1960). The heat to the combustion chamber is assumed to be available at 2500°F. In the example, air from the dead state (14.7 psia, 75°F) enters the intake structure. Pressure drops before the turbine inlet in the intake ducting to 14.5 psia. It is compressed in a compressor with a... 

Absorption Air-Conditioning Brayton Gas Refrigeration Cycle Stirling Refrigeration Cycle Ericsson Cycle Liquefaction of Gases Nonazeotropic Mixture Refrigeration Cycle Design Examples Summary... 

The basic gas Brayton refrigeration cycle analysis is given by Example 6.12. 

A common method of producing mechanical work (usually for electrical power gene-ration) is to use a gas turbine and the Brayton or gas turbine power cycles. This open cycle consists of a compressor (on the same shaft as the turbine), a combustor in which fuel is added and ignited to heat the gas, and a turbine that extracts work from the high-temperature, high-pressure gas, which is then exhausted to the atmosphere. The open-cycle gas turbine is used, for example, in airplane jet engines and in some trucks. This cycle is shown in Fig. 5.2-87 -... 

Energy conversion efficiency is an important factor that defines the specific (i.e. per unit of the useful energy produced) values of the resource consumption, emissions and discharges. These values are inversely proportional to the efficiency, so that, for example, gas cooled SMRs with direct Brayton power cycles (energy conversion efficiency -50%) may offer a substantial reduction in the discharged (rejected) heat when compared to present day LWRs (energy conversion efficiency -32%). Heat discharges could also be minimized by purposeful use of the rejected heat (see Annex XV). 

Regarding the potential to share design and technology development with reactors of other types, a remarkable example is provided by the AHTR, a pre-conceptual system that is part of the U S. Department of Energy Generation IV reactor programme. About 70% of the R D required for the AHTR is shared with that for helium cooled high temperature reactors. This includes fuel development, materials development, and Brayton power cycles. Annex XXVI. 

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