Chapter 9 Learning Outcomes Learning Outcomes Learning Outcomes

Chapter 9 Learning Outcomes Learning Outcomes Learning Outcomes www.phwiki.com

Chapter 9 Learning Outcomes Learning Outcomes Learning Outcomes

Miss E,, Midday Host has reference to this Academic Journal, PHwiki organized this Journal Chapter 9 Gas Power Systems Learning Outcomes Conduct air-st in addition to ard analyses of internal combustion engines based on the Otto, Diesel, in addition to dual cycles, including the ability to sketch p-v in addition to T-s diagrams in addition to evaluate property data at principal states. apply energy, entropy, in addition to exergy balances. determine net power output, thermal efficiency, in addition to mean effective pressure. Learning Outcomes Conduct air-st in addition to ard analyses of gas turbine power plants based on the Brayton cycle in addition to its modifications, including the ability to sketch T-s diagrams in addition to evaluate property data at principal states. applying mass, energy, entropy, in addition to exergy balances. determine net power output, thermal efficiency, back work ratio, in addition to the effects of compressor pressure ratio on per as long as mance.

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Learning Outcomes Analyze subsonic in addition to supersonic flows through nozzles in addition to diffusers, including the ability to describe the effects of area change on flow properties in addition to the effects of back pressure on mass flow rate. explain the occurrence of choking in addition to normal shocks. analyze the flow of ideal gases with constant specific heats. Considering Gas Turbine Power Plants Gas turbine power plants are more quickly constructed, less costly, in addition to more compact than the vapor power plants considered in Chapter 8. Gas turbines are suited as long as stationary power generation as well as as long as powering vehicles, including aircraft propulsion in addition to marine power plants. Gas turbines are increasingly used as long as large-scale power generation, in addition to as long as such applications fueled primarily by natural gas, which is relatively abundant today. Considering Gas Turbine Power Plants Gas turbines may operate on an open or closed basis, as shown in the figures. The open gas turbine is more commonly used in addition to is the main focus of our study of gas turbines. Study of the individual components of these configurations requires the control volume as long as ms of the mass, energy, in addition to entropy balances. Open to the atmosphere Closed

Considering Gas Turbine Power Plants The open mode gas turbine is an internal combustion power plant. Air is continuously drawn into the compressor where it is compressed to a high pressure. Combustion products exit at elevated temperature in addition to pressure. Combustion products exp in addition to through the turbine in addition to then are discharged to the surroundings. Air then enters the combustion chamber (combustor) where it mixes with fuel in addition to combustion occurs. Considering Gas Turbine Power Plants The closed gas turbine operates as follows: A gas circulates through four components: turbine, compressor, in addition to two heat exchangers at higher in addition to lower operating temperatures, respectively. The turbine in addition to compressor play the same roles as in the open gas turbine. As the gas passes through the higher-temperature heat exchanger, it receives energy by heat transfer from an external source. The thermodynamic cycle is completed by heat transfer to the surroundings as the gas passes through the lower-temperature heat exchanger. Considering Gas Turbine Power Plants The heat transfer associated with the higher-temperature heat exchanger of the closed gas turbine originates from an external source, which may include External combustion of biomass, municipal solid waste, fossil fuels such as natural gas, in addition to other combustibles. Waste heat from industrial processes. Solar thermal energy. A gas-cooled nuclear reactor.

To conduct elementary analyses of open gas turbine power plants, simplifications are required. Although highly idealized, an air-st in addition to ard analysis can provide insights in addition to qualitative in as long as mation about actual per as long as mance. An air-st in addition to ard analysis has the following elements: The working fluid is air which behaves as an ideal gas. Ideal gas relations are reviewed in Table 9.1. The temperature rise that would be brought about by combustion is accomplished by heat transfer from an external source. With an air-st in addition to ard analysis, we avoid the complexities of the combustion process in addition to the change in composition during combustion, which simplifies the analysis considerably. Combustion is studied in Chapter 13. In a cold air-st in addition to ard analysis, the specific heats are assumed constant at their ambient temperature values. Air-St in addition to ard Analysis of Open Gas Turbine Power Plants Air-St in addition to ard Brayton Cycle The schematic of a simple open air-st in addition to ard gas turbine power plant is shown in the figure. The energy transfers by heat in addition to work are in the directions of the arrows. Air circulates through the components: Process 1-2: the air is compressed from state 1 to state 2. Process 2-3: The temperature rise that would be achieved in the actual power plant with combustion is realized here by heat transfer, At state 1, air is drawn into the compressor from the surroundings. Air-St in addition to ard Brayton Cycle Air returns to the surroundings at state 4 with a temperature typically much greater than at state 1. After interacting with the surroundings, each unit of mass returns to the same condition as the air entering at state 1, thereby completing a thermodynamic cycle. Process 3-4: The high-pressure, high-temperature air exp in addition to s through the turbine. The turbine drives the compressor in addition to develops net power,

Air-St in addition to ard Brayton Cycle Air returns to the surroundings at state 4 with a temperature typically much greater than at state 1. After interacting with the surroundings, each unit of mass returns to the same condition as the air entering at state 1, thereby completing a thermodynamic cycle. Process 3-4: The high-pressure, high-temperature air exp in addition to s through the turbine from state 3 to state 4. The turbine drives the compressor in addition to develops net power, We imagine process 4-1 being achieved by a heat exchanger, as shown by the dashed line in the figure. Air-St in addition to ard Brayton Cycle Cycle 1-2-3-4-1 is called the Brayton cycle. The compressor pressure ratio, p2/p1, is a key Brayton cycle operating parameter. Air-St in addition to ard Brayton Cycle Analyzing each component as a control volume at steady state, assuming the compressor in addition to turbine operate adiabatically, in addition to neglecting kinetic in addition to potential energy effects, we get the following expressions as long as the principal work in addition to heat transfers, which are positive in accord with our convention as long as cycle analysis. Turbine Compressor (Eq. 9.15) (Eq. 9.16) (Eq. 9.17) (Eq. 9.18) Heat addition Heat rejection

Air-St in addition to ard Brayton Cycle The thermal efficiency is (Eq. 9.19) The back work ratio is (Eq. 9.20) Since Eqs. 9.15 through 9.20 have been developed from mass in addition to energy balances, they apply equally when irreversibilities are present in addition to in the absence of irreversibilities. Note: A relatively large portion of the work developed by the turbine is required to drive the compressor. For gas turbines, back work ratios range from 20% to 80% compared to only 1-2% as long as vapor power plants. Ideal Air-St in addition to ard Brayton Cycle The ideal air-st in addition to ard Brayton cycle provides an especially simple setting as long as study of gas turbine power plant per as long as mance. The ideal cycle adheres to additional modeling assumptions: Frictional pressure drops are absent during flows through the heat exchangers. These processes occur at constant pressure. These processes are isobaric. Flows through the turbine in addition to pump occur adiabatically in addition to without irreversibility. These processes are isentropic. Accordingly, the ideal Brayton cycle consists of two isentropic processes alternated with two isobaric processes. In this respect, the ideal Brayton cycle is in harmony with the ideal Rankine cycle, which also consists of two isentropic processes alternated with two isobaric processes (Sec. 8.2.2). Process1-2: Isentropic compression of air flowing through the compressor. Process 2-3: Heat transfer to the air as it flows at constant pressure through the higher-temperature heat exchanger. Ideal Air-St in addition to ard Brayton Cycle The ideal air-st in addition to ard Brayton cycle consists of four internally reversible processes: Process 3-4: Isentropic expansion of the air through the turbine. Process 4-1: Heat transfer from the air as it flows at constant pressure through the lower-temperature heat exchanger.

Ideal Air-St in addition to ard Brayton Cycle Since the ideal Brayton cycle involves internally reversible processes, results from Sec. 6.13 apply. On the p-v diagram, the work per unit of mass flowing is –vdp. Thus on a per unit of mass flowing basis, Area 1-2-a-b-1 represents the compressor work input. Area 3-4-b-a-3 represents the turbine work output. Enclosed area 1-2-3-4-1 represents the net work developed. Area 2-3-a-b-2 represents the heat added. Area 4-1-b-a-4 represents the heat rejected. Enclosed area 1-2-3-4-1 represents the net heat added or equivalently, the net work developed. Ideal Air-St in addition to ard Brayton Cycle On the T-s diagram, the heat transfer per unit of mass flowing is Tds. Thus, on a per unit of mass flowing basis, Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance That the compressor pressure ratio, p2/p1, is an important operating parameter as long as gas turbines is brought out simply by the following discussions centering on the T-s diagram:

Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance Increasing the compressor pressure ratio from p2/p1 to p2/p1 changes the cycle from 1-2-3-4-1 to 1-2-3-4-1. Since the average temperature of heat addition is greater in cycle 1-2-3-4-1, in addition to both cycles have the same heat rejection process, cycle 1-2-3-4-1 has the greater thermal efficiency. Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance Increasing the compressor pressure ratio from p2/p1 to p2/p1 changes the cycle from 1-2-3-4-1 to 1-2-3-4-1. Since the average temperature of heat addition is greater in cycle 1-2-3-4-1, in addition to both cycles have the same heat rejection process, cycle 1-2-3-4-1 has the greater thermal efficiency. Accordingly, the Brayton cycle thermal efficiency increases as the compressor pressure ratio increases. Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance Increasing the compressor pressure ratio from p2/p1 to p2/p1 changes the cycle from 1-2-3-4-1 to 1-2-3-4-1. Since the average temperature of heat addition is greater in cycle 1-2-3-4-1, in addition to both cycles have the same heat rejection process, cycle 1-2-3-4-1 has the greater thermal efficiency. Accordingly, the Brayton cycle thermal efficiency increases as the compressor pressure ratio increases. The turbine inlet temperature also increases with increasing compressor ratio – from T3 to T3.

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Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance However, there is a limit on the maximum temperature at the turbine inlet imposed by metallurgical considerations of the turbine blades. Let’s consider the effect of increasing compressor pressure ratio on Brayton cycle per as long as mance when the turbine inlet temperature is held constant. This is investigated using the T-s diagram as presented next. Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance The figure shows the T-s diagrams of two ideal Brayton cycles having the same turbine inlet temperature but different compressor pressure ratios. Cycle A has the greater compressor pressure ratio in addition to thus the greater thermal efficiency. Cycle B has the larger enclosed area in addition to thus the greater net work developed per unit of mass flow. For Cycle A to develop the same net power as Cycle B, a larger mass flow rate would be required in addition to this might dictate a larger system. Effects of Compressor Pressure Ratio on Brayton Cycle Per as long as mance Accordingly, as long as turbine-powered vehicles, where size in addition to weight are constrained, it may be desirable to operate near the compressor pressure ratio as long as greater net work per unit of mass flow in addition to not the pressure ratio as long as greater thermal efficiency.

Gas Turbine Power Plant Irreversibility The most significant irreversibility by far is the irreversibility of combustion. This type of irreversibility is considered in Chap. 13, where combustion fundamentals are developed. Irreversibilities related to flow through the turbine in addition to compressor also significantly impact gas turbine per as long as mance. They act to decrease the work developed by the turbine in addition to increase the work required by the compressor, thereby decreasing the net work of the power plant. Gas Turbine Power Plant Irreversibility Isentropic turbine efficiency, introduced in Sec. 6.12.1, accounts as long as the effects of irreversibilities within the turbine in terms of actual in addition to isentropic turbine work, each per unit of mass flowing through the turbine. Gas Turbine Power Plant Irreversibility Isentropic compressor efficiency, introduced in Sec. 6.12.3, accounts as long as the effects of irreversibilities within the compressor in terms of actual in addition to isentropic compressor work input, each per unit of mass flowing through the compressor.

The energy rate balance applicable to the nozzle takes the as long as m Gas Turbines as long as Aircraft Propulsion For the nozzle, i = 4 in addition to e = 5. Then, Since inlet velocity is negligible, the energy rate balance reduces to Since the final expressions obtained as long as the diffuser in addition to nozzle are deduced from mass in addition to energy rate balances, they apply equally when irreversibilities are present in addition to in the absence of irreversibilities. Gas Turbines as long as Aircraft Propulsion

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