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

In summary, the conversation discusses the calculation of power used by a heat engine that is rejecting 200btu/h and is 30% efficient. The formula QH=w+QC is mentioned, as well as a power diagram showing the relationship between wasted heat, work, and total energy output. The calculated value for power, 17.9 watts, is considered too small, but it is correct as it takes into account both work and wasted heat.
  • #1
Windseaker
46
0
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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  • #2
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.
 
  • #3
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??
 

1. How does a heat engine work?

A heat engine works by converting heat energy into mechanical energy. This is done by using a fuel source to create heat, which is then used to produce a high pressure gas. The gas expands and pushes a piston, which in turn creates mechanical work.

2. What is the efficiency of a heat engine?

The efficiency of a heat engine is the ratio of the work output to the heat input. This is known as the Carnot efficiency and is given by the formula: efficiency = 1 - (Tc/Th), where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir.

3. How much power can a heat engine produce?

The power output of a heat engine depends on several factors such as the efficiency of the engine, the temperature of the hot and cold reservoirs, and the amount of fuel being used. The maximum theoretical power output of a heat engine is given by the formula: P = Qh(1 - Tc/Th), where Qh is the heat input.

4. What is the difference between an internal combustion engine and an external combustion engine?

An internal combustion engine uses the combustion of fuel within the engine itself to produce heat, while an external combustion engine uses a separate heat source to produce heat, such as a boiler. Internal combustion engines are more common in cars, while external combustion engines are used in power plants and some large vehicles like ships.

5. How is the power output of a heat engine measured?

The power output of a heat engine can be measured in watts, which is a unit of power. This can be done by measuring the work output of the engine, which is the force applied multiplied by the distance traveled, and dividing it by the time it takes to complete the work. Other common units for measuring power include horsepower and kilowatts.

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