Mechanical Engineering Review Online

Consider a three-process air-standard power cycle given by: Process 1-2: Isentropic compression. Process 2-3: Constant pressure heat addition. Process 3-1: Constant volume heat rejection. The initial pressure and temperature of the air is P₁ = 150 kPa and T₁=300 K, respectively and the pressure at the end of the isentropic compression P₂=1200 kPa, Determine:

1. The isentropic compression ratio, r_k

a. 4.28

b. 4.55

c. 4.82

d. 4.41

2. The thermal efficiency of the cycle

a. 19.16

b. 18.35

c. 21.32

d. 25.41

3. The mean effective pressure, in kPa

a. 691.34

b. 752.11

c. 790.11

d. 630.22

4. Consider a three-process air standard power cycle in which process 1-2 is an isothermal compression, 2-3 is a constant pressure heat addition and 3-1 is an isentropic expansion. Given that the initial pressure and temperature is P₁=130 kPa and t₁=30^oC, respectively and P₂ = 1000 kPa. Determine the thermal efficiency of the cycle

a. 28.32%

b. 26.40%

c. 32.20%

d. 22.20%

5. A three-process power cycle operating with 0.5 kg/s of nitrogen as the working substance operates in the following processes: Process 1-2: Constant temperature compression (t₁=27^oC, P₁=100 kPa). Process 2-3: Constant volume heat addition. Process 3-1: Polytropic expansion (n=1.30). The maximum pressure of the cycle is 300 kPa and the isothermal compression requires -74 kJ/kg of work. Determine for the cycle: The work net in kW

a. 7.23

b. 5.79

c. 6.36

d. 4.22

6. Consider a three-process air-standard power cycle with the following processes: Process 1-2: Constant pressure heat rejection where P₁=P₂=1000 kPa and t₁=600^oC. Process 2-3: Polytropic expansion, PV^1.3=C. Process 3-1: Constant volume. If the mass of air is 3 kgs and the heat rejected in the cycle is 200 kJ. Determine, the heat added, in kJ

a. 197.14

b. 220.32

c. 180.22

d. 211.18

A three-process power cycle using 2 kg/s of air as the working substance, has the following reversible processes: Process 1-2: Constant volume heat addition. Process 2-3: Adiabatic expansion. Process 3-1: Constant pressure heat rejection. Given: P₁=100 kPa, T₁=300K and P₂=500 kPa. Determine:

7. The net work output, in kW

a. 474.2

b. 450.8

c. 430.2

d. 422.5

8. The thermal efficiency

a. 26.4%

b. 21.6%

c. 24.5%

d. 28.2%

A thermodynamic cycle uses 0.5 kg of air works in a three-process air-standard power cycle: Process 1-2: Isothermal expansion. Process 2-3: Constant volume. Process 3-1: Isentropic, k=1.4. Given: Pressure and temperature at the end of constant volume process is P₃=100 kPa and T₃=300K, respectively. If the isentropic compression ratio is 6.0, determine:

9. The work net output, in kJ

a. 45

b. 50

c. 40

d. 55

10. The thermal efficiency.

a. 28.5%

b. 32.5%

c. 36.7%

d. 25.8%

11. An air-standard power cycle works on the following processes: Process 1-2: Isothermal compression. Process 2-3: Constant volume. Process 3-1: Constant pressure. If the pressure limits of the cycle are 60 psi and 15 psi, and the volume at the beginning of isothermal compression is 5ft³, determine the work net output, in Btu.

a. -8.8

b. -10.9

c. -9.2

d. -12.3

Answer Key (Handwritten)