Text Exercise 1

Pagina 1

Joule-Brayton Part 1 – Ideal cycle in closed system An ideal Joule-Brayton cycle works with a compression ratio (p 2/p1) equal to 16 and the temperature of the cycle points are respectively T1 = 300 K, T2 = 662 K, T3 = 1’250 K and T4 = 566 K. Considering that the working fluid is air (C p = 1.007 kJ/kgK) and the useful power produced by the cycle is 200 MW, evaluate: • the energy exchanges of each single transformation of the cycle • first law and second law efficiency • the air mass flow rate • the overall generation of irreversibilities (specifying if internal and/or external) assuming the hot and cold heat reservoirs at constant temperature, respectively equal to Th = T3 and Tc = T1. • the overall destroyed exergy, assuming ambient temperature T0 = 300 K, separating the contributions of each single transformation. Part 2 – real cycle in open system A real Joule-Brayton cycle is taken that shares the same compression ratio (p 2/p1) and temperatures T1 and T3 as in the Part 1. Comparison is also performed at same input thermal power (Qin). Consider also: • real turbine and compressor are introduced, with isentropic efficiency equal to 0.9. • heat is provided by combustion, assuming LHVCH4 = 50 MJ/kg. Compute the net produced power, air and fuel flow rate, cycle efficiency and destroyed exergy, separating the contributions. Part 3 – partial load of real cycle (for individual study, results provided) Repeat all the calculations for the real cycle at 50% power load, assuming that turbine and compressor isentropic efficiency are lower and equal to 85%.