Practice questions for GATE Mechanical Engineering from the topic of SFEE (First Law of thermodynamics) and Power plant engineering from the the subject of engineering thermodynamics.
Q1) Air enters an isentropic nozzle at 1.30 atm and 25oC with a velocity of 2.5 m/s. The nozzle entrance diameter is 120 mm. The air exits the nozzle at 1.24 atm with a velocity of 90 m/s. Determine the temperature of the exiting air and the nozzle exit diameter.
Q2) Consider a steam turbine power plant operation near critical pressure, as shown in the figure. As a first approximation, it may be assumed that the turbine and pump processes are reversible and adiabatic. Neglecting any changes in KE and PE, calculate:
- The specific turbine work output and the turbine exit state
- The pump work input and enthalpy at the pump exit state
- The thermal efficiency of the cycle
Q3) Consider an ideal steam reheat cycle where steam enters the high pressure turbine at 4.0 MPa, 400oC, and then expands to 0.8 MPa. It is then reheated to 400oC and expands to 10 kPa in the low pressure turbine. Calculate the cycle thermal efficiency and the moisture content of the steam leaving the low pressure turbine.
Q4) An afterburner in a jet engine adds fuel after the turbine this raising the pressure and temperature due to the energy of combustion. Assume a standard condition of 800 K, 250 kPa after the turbine into the nozzle that exhausts at 95 kPa. Assume the afterburner adds 425 kJ/kg to that state with a rise in pressure for the same specific volume, and neglect any upstream effects on the turbine. Find the nozzle exit velocity before and after the afterburner is turned on.
Q5) An air standard Ericsson cycle has an ideal regenerator. Heat is supplied at 950oC and heat is rejected at 80oC. Pressure at the beginning of the isothermal compression process is 70 kPa. The heat added is 700 kJ/kg. Find the compressor work, the turbine work and the cycle efficiency.