Engineering Board Exam Reviewer · Thermodynamics · medium

A refrigerator removes heat from a cold space at 5 kW with a COP of 2.5. What is the power input required?

  1. 12.5 kW
  2. 7 kW
  3. 0.5 kW
  4. 2 kW

Answer

D. 2 kW

Solution

W = QL/COP = 5/2.5 = 2 kW.

More Thermodynamics questions

  1. A Carnot heat pump extracts heat from outside air at 270 K and delivers heat to a house at 300 K. What is its COP?
  2. An inventor claims that an engine operating between 500 K and 250 K has a thermal efficiency of 60%. The claim is:
  3. A Carnot engine has an efficiency of 40% and rejects heat to a sink at 300 K. What is the source temperature?
  4. A Carnot engine receives 1000 kJ of heat from a source at 600 K and rejects heat to a sink at 300 K. How much work does it produce?
  5. What is the maximum possible efficiency of a heat engine operating between 800 K and 300 K?
  6. 1000 kJ of heat is transferred directly from a reservoir at 600 K to a reservoir at 300 K. What is the total entropy generated?
  7. Air changes from 100 kPa, 300 K to 500 kPa, 500 K. What is the change in specific entropy? (cp = 1.0 kJ/kg· K, R = 0.287 kJ/kg· K)
  8. One kilogram of air expands isothermally to three times its initial volume. What is the change in entropy? (R = 0.287 kJ/kg· K)
  9. One kilogram of water is heated from 300 K to 350 K. What is its change in entropy? (c = 4.187 kJ/kg· K)
  10. A system receives 500 kJ of heat reversibly at a constant temperature of 400 K. What is its change in entropy?

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