Heat engine, how much power does it use in watts?

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SUMMARY

A heat engine with a rejection of 200 BTU/h and an efficiency of 30% uses approximately 76.2 watts of total power. The calculation involves converting BTU to watts using the conversion factor of 1 kWh = 3412 BTU, resulting in 58.6 watts of waste heat. The effective power used by the engine is determined by multiplying the total energy output (work plus waste heat) by the efficiency, yielding a final value of 17.9 watts for the power consumed. This confirms that the initial calculation of 17.6 watts was incorrect due to not accounting for total energy output.

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  • Understanding of heat engine efficiency and thermodynamics
  • Familiarity with BTU and watt conversion factors
  • Knowledge of energy equations, specifically QH = W + QC
  • Basic grasp of power calculations over time
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1.A heat engine is rejecting 200btu/h and 30% efficient, how much power does it use in watts?

2. QH=w+QC and power=energy/time (1kwh=3412btu)
and a power diagram: QC= wasted heat, w=work

QH
l
30%l---->W
l
QC

3. 200btu/h(1kwh/3412btu)(1000w/1kw)=58.6watts (30%)=17.6watts
This value just seems too small??
 
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It is too small, but not by much. You're multiplying 58.6% watts, which is the waste heat produced by the heat engine, by efficiency. You need to multiply total energy output (work+waste heat) by efficiency to get the answer.
 
Your saying:

Work=17.6watts +waste heat=58.6watts---=76.2watts total

then 76.2watts (x) eff.=30%----=17.9watts used power??

Is this right??
 

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