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

AI Thread Summary
A heat engine rejecting 200 BTU/h with 30% efficiency uses approximately 76.2 watts in total, which includes both work and wasted heat. The calculation involves converting BTU to watts, resulting in 58.6 watts of waste heat. To find the power used, the total energy output (work plus waste heat) is multiplied by the efficiency. This leads to a power usage of about 17.9 watts, which some participants find surprisingly low but within acceptable limits. The discussion emphasizes the importance of correctly applying efficiency to total energy output for accurate calculations.
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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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