Solving Carnot Heat Problem: 1637.8BTU Answered

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SUMMARY

The discussion centers on solving the Carnot heat problem involving a heat engine connected to a 300-watt motor with a 40% efficiency rating. The calculations reveal that the heat extracted from the heat source amounts to 1637.8 BTU after powering the motor for 4 hours. The formula used includes QH = W + QC, where QH represents the total heat, W is the work done, and QC is the waste heat. The conversion from watts to BTU is confirmed as 300W equating to 1023.6 BTU over the specified time period.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically the Carnot cycle.
  • Familiarity with heat engine efficiency calculations.
  • Knowledge of unit conversions between watts and BTU.
  • Basic grasp of work-energy principles in physics.
NEXT STEPS
  • Study the Carnot efficiency formula and its implications in real-world applications.
  • Learn about the differences between BTU and joules for thermal energy measurements.
  • Explore the impact of efficiency on heat engine performance and design.
  • Investigate residential heating systems and their efficiency ratings in the U.S.
USEFUL FOR

Students studying thermodynamics, engineers designing heat engines, and professionals involved in residential heating system optimization will benefit from this discussion.

Windseaker
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Homework Statement


Problem: A heat engine is connected to a 300watt motor. If we power the motor for 4hrs and heat engine is 40% efficient,how much heat is extracted from heat source in?

Homework Equations


Given: Q= heat QC=waste heat QH=W+QC and Power=E/t or Work/t

The Attempt at a Solution

This is a diagram equation of heat.
QH-----l----->QC
l
l
V
300w

300W(3.412btu/1W)= 1023.6btu (4hr) = 4094.4 btuh
----- 4094.4btu(40%)=1637.8btuh
 
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The engine uses more heat energy than the work it yields: the work is 40 % of the heat: W=0.4*Q.

Do you really use btu units for heat instead of joule?

ehild
 
So, are you saying that time is not used here (4hrs)? its just the starting heat loss.

yes btu, this is more about residential usage in US.
 

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