Calculating Efficiency of a Heat Engine with COP = 5.0 and 25kJ Heat Removal

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SUMMARY

The discussion focuses on calculating the efficiency of a heat engine with a coefficient of performance (COP) of 5.0 that removes 25 kJ of heat from a cold reservoir. The relationship between the heat removed (QL), work done (W), and heat added (QH) is established using the formula COP = QL/W, leading to a work output of 5 kJ. The correct efficiency formula is confirmed as e = W/QH, emphasizing that QH is not equal to QL. The efficiency calculation ultimately reveals that the efficiency of the heat engine is 20%.

PREREQUISITES
  • Understanding of Coefficient of Performance (COP)
  • Knowledge of thermodynamic principles, specifically conservation of energy
  • Familiarity with efficiency formulas in thermodynamics
  • Basic calculations involving heat transfer and work
NEXT STEPS
  • Study the relationship between heat engines and refrigerators
  • Learn about the Carnot efficiency and its implications
  • Explore advanced thermodynamic cycles and their efficiencies
  • Investigate real-world applications of COP in HVAC systems
USEFUL FOR

Students studying thermodynamics, engineers designing heat engines, and anyone interested in the principles of energy conversion and efficiency calculations.

kasse
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Homework Statement



A machine with COP = 5.0 removes 25kJ of heat from a cold reservoar. If the machine is reversible and driven the other way as a heat engine, what is the efficiency?

The Attempt at a Solution



COP = QL/W --> W = 5kJ

e = QH/W

Is QH the same as QL som that e = 20%
 
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Hi kasse,

No, I don't believe that [itex]Q_H[/itex] and [itex]Q_L[/itex] are the same. Using conservation of energy, you can find out how Qh, QL, and W are related. What do you get?

Also, your efficiency formula needs to be:

[tex] e=\frac{W}{Q_H}[/tex]
 

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