Gas turbine power plant Flashcards
What are the processes in a Joule/Brayton cycle?
1-2 : adiabatic/isentropic compression
2-3: isobaric heat supply
3-4: adiabatic/isentropic expansion
4-1: isobaric heat removal
What is the difference between an open and closed gas turbine cycle?
Open: working fluid is fresh air
Closed: working fluid is recycled
Write eqution for relationship between temperature and pressure in a turbine
T_high / T_low = (p_high / p_low) ^ (k-1)/k
Equation for isentropic compressor efficiency. (Using 1 and 2 as index)
n_ic = (h2s - h1) / (h2-h1) = (T2s - T1) / (T2 - T1)
Equation for isentropic turbine efficiency. (Using 1 and 2 as index)
n_it = (h1 - h2) / (h1 - h2s) = (T1 - T2) / (T1 - T2s)
What is the meaning of Beta? What is the typical value of Beta?
Beta is the pressure ratio of a compressor/turbine inlet and outlet. Usually 15-30
How does regeneration increase the efficiency? (2 answers)
- Increasing average temperature of heat addition (Less heat needed in combustion chamber)
- Decreasing average temperature of heat rejection
(= Heat from turbine exhaust gives heat to compressor exhaust, before entering the comubstion chamber)
What is the regenerator’s effectiveness? What does it mean if it equals 1?
1 = gas entering, from compressor
2 = gas leaving, to combustion chamber
3 = gas entering, from last turbine
E = (T2 - T1) / (T3 - T1)
If E = 1: T2= T3. Perfect exchange of heat.
What is intercooling and where is it placed?
Compression is divided into 2 or more stages with cooling between. Reduces the work for the compressor due to removed moisture in the air.
What is reheat and where is it placed? What is the optimum reheat conditions?
Heat addition between expansion steps (turbines). Increased work output, decreased efficiency. Optimum: Equal temperature drops (or pressure ratio) in LP and HP turbine stages.
