MAE 115 APPLIED ENGINEERING THERMODYNAMICS Hw#3

Java Python APPLIED ENGINEERING THERMODYNAMICS

MAE 115

1. Consider an ideal Ericsson cycle with air as the working fluid executed in a steady-flow system. Air is at 27°C and 120 kPa at the beginning of the isothermal compression process, during which 150 kJ/kg of heat is rejected. Heat transfer to air occurs at 1200 K. Determine (a) the maximum pressure in the cycle, (b) the net work output per unit mass of air, and (c) the thermal efficiency of the cycle.

2. An air-standard Stirling cycle operates with a maximum pressure of 3600 kPa and a minimum pressure of 50 kPa. The maximum volume is 12 times the minimum voltage, and the low-temperature reservoir is at 20°C. Allowing a 5°C temperature difference between the external reservoirs and the air when appropriate, calculate the specific heat added to the cycle and its net specific work.

3. A gas turbine power plant operates on the simple Brayton cycle between the pressure limits of 100 and 2000 kPa. The working fluid is air, which enters the compressor at 40°C at a rate of 700 m3/min and leaves the turbine at 650°C. Using variable specific heats for air and assuming a compressor isentropic efficiency of 85% and a turbine isentropic efficiency of 88%, determine (a) the net power output, (b) the back work ratio, and (c) the thermal efficiency.

4. The idea of using gas turbines to power automobiles was conceived in the 1930s, and considerable research was done in the 1940s and 1950s to develop automotive gas turbines by major automobile manufacturers such as the Chrysler and Ford corporations in the United States and Rover in the United Kingdom. The world’s first gas turbine-powered automobile, the 200-hp Rober Jet 1, was built in 1950 in the United Kingdom. This was followed by the production of the Plymouth Sport Coupe by Chrysler in 1 MAE 115 APPLIED ENGINEERING THERMODYNAMICS Hw#3 954 under the leadership of G.J. Huebner. Several hundred gas turbine-powered Plymouth cars were built in the early 1960s for demonstration purposes and were loaned to a select group of people to gather field experience. The users had no complaints other than slow acceleration. But the cars were never mass-produced because of the high production (especially material) costs and failure to satisfy the provisions of the 1966 Clean Air Act.

A gas turbine-powered Plymouth car built in 1060 had a turbine inlet temperature of 1700°F, a pressure ratio of 4, and a regenerator effectiveness of 0.9. Using isentropic efficiencies of 80% for both the compressor and the turbine, determine the thermal efficiency of this car. Also, determine the mass flow rate of air for a net power output of 95 hp. Assume the ambient air to be at 540°F and 14.5 psia.

5. A stationary gas turbine power plant operates on an ideal regenerative Brayton cycle (ε=100%) with air as the working fluid. Air enters the compressor at 95 kPa and 290 K and the turbine at 760 kPa and 1100 K. Heat is transferred to air from an external source at a rate of 75,000 kJ/s. Determine the power delivered by this plant (a) assuming constant specific heats for air at room temperature and (b) accounting for the variation of specific heats with temperature.

6. Air enters a gas turbine with two stages of compression and two statges of expansion at 100 kPa and 17°C. This system uses a regenerator as well as reheating and intercooling. The pressure ratio across each compressor is 4; 300 kJ/kg of heat are added to the air in each combustion chamber; and the regenerator operates perfectly while increasing the temperature of the cold air by 20°C. Determine this system’s thermal efficiency. Assume isentropic operations for all compressors and the turbine stages and use constant specific heats at room temperature