Energy conversion devices Knowledge-Based Download PDF

Questions

1. 1.

   An industrial air compressor converts electrical energy into stored pneumatic energy. If the compressor receives an electrical input power of 12 kW and stores 2.7 MJ of useful pneumatic energy in 5.0 minutes, what is its energy conversion efficiency?

   • A) 25%
   • B) 45%
   • C) 75%
   • D) 80%
2. 2.

   An electric hoist operates with an electrical input power of 4.0 kW and delivers 3.2 kW of useful mechanical power. How much energy is dissipated as waste heat and sound when the hoist runs continuously for 2.0 minutes?

   • A) 1.6 kJ
   • B) 384 kJ
   • C) 96 kJ
   • D) 480 kJ
3. 3.

   A regenerative braking system on a 1500 kg electric car brings the vehicle from a speed of 20 m/s to a complete stop. If the system recovers 180 kJ of electrical energy and stores it in the battery, what is the energy conversion efficiency of the system?

   • A) 30%
   • B) 40%
   • C) 60%
   • D) 75%
4. 4.

   A power plant converts thermal energy into electrical energy using two consecutive stages: a steam generator operating with an efficiency of 75% and a turbine-generator unit operating with an efficiency of 40%. What is the overall efficiency of the power plant?

   • A) 58%
   • B) 35%
   • C) 30%
   • D) 25%
5. 5.

   An internal combustion engine delivers a mechanical power output of 45 kW while operating with an efficiency of 30%. At what rate does the engine consume chemical energy from its fuel?

   • A) 150 kW
   • B) 105 kW
   • C) 31.5 kW
   • D) 13.5 kW
6. 6.

   An electric generator converts mechanical energy into electrical energy. If the generator receives a mechanical input power of 80 kW and dissipates energy as heat and sound at a rate of 16 kW, what is its efficiency?

   • A) 20%
   • B) 80%
   • C) 84%
   • D) 75%
7. 7.

   A wind turbine extracts kinetic energy from the wind at an average rate of 2.0 MW. If the turbine-generator system operates with an efficiency of 35%, what total electrical energy does it deliver to the power grid in 15 minutes?

   • A) 10.5 MJ
   • B) 1170 MJ
   • C) 1800 MJ
   • D) 630 MJ
8. 8.

   Water falls through a hydroelectric turbine at a rate of 500 kg/s from a height of 20 m. If the turbine-generator system operates with an efficiency of 70%, what is the electrical power output produced by the system? (Take $g = 10\text{ m/s}^2$.)

   • A) 70 kW
   • B) 100 kW
   • C) 30 kW
   • D) 143 kW
9. 9.

   A photovoltaic panel with an energy conversion efficiency of 18% receives 800 W of radiant power from sunlight. At what rate is energy wasted as thermal energy by the panel?

   • A) 656 W
   • B) 144 W
   • C) 782 W
   • D) 512 W
10. 10.

    An electric motor supplied with an electrical input power of 500 W lifts a 20 kg mass vertically at a constant speed of 1.5 m/s. What is the efficiency of the motor? (Take g = 10 m/s2.)

    • A) 25%
    • B) 30%
    • C) 40%
    • D) 60%