Solving Carnot Heat Problem: 1637.8BTU Answered

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    Carnot Heat
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The discussion centers on calculating the heat extracted from a heat source by a heat engine connected to a 300-watt motor, operating at 40% efficiency for 4 hours. The calculations show that the total heat extracted is 1637.8 BTU, with the engine utilizing more heat energy than the work it produces. There is a debate about the use of BTU versus joules for heat measurement, with an emphasis on BTU being more common in residential contexts in the US. The time factor of 4 hours is confirmed to be relevant in the calculations. Overall, the focus is on understanding the efficiency and energy output of the heat engine.
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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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