What is the engine's thermal efficiency?

In summary, the conversation discusses a heat engine using helium as the working substance and its thermal efficiency. The attempt at a solution involves calculating work using the formula for a triangle, but the correct method is to integrate dW = P*dV. The question is raised about the assumption of Q_h being a temperature of 2200 K instead of a heat transfer value.
  • #1
Bigworldjust
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Homework Statement



A heat engine using 110g of helium as the working substance follows the cycle shown in the figure.

http://session.masteringphysics.com/problemAsset/1074114/5/19.P59.jpg

What is the engine's thermal efficiency?

Homework Equations



n=W/Q_h

The Attempt at a Solution



Alright so up to this point I have figured out p1,p2,p3, T1,T2,T3, V1,V2, and V3.

I tried doing W = area of triangle = .5(5-1)atm*(5.0*10^-3-1.0*10^-3)m^3 and got .008J. I assumed Q_h was 2200K because that is what I got for the temperature between T2 and T3, and that is where the heat should be going in. So I divided and 36.36% but that is wrong. Any help here? Thanks!
 
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  • #2
Bump any help?
 
  • #3
Work is not a triangle in this case. You'll have to integrate dW = P*dV, where P = nRT/V.

Also, why is Q_h a temperature of 2200 K and not a heat transfering into the engine cycle?

Heat units = Joules

Temperature units = Kelvin
 

Related to What is the engine's thermal efficiency?

1. What is thermal efficiency?

Thermal efficiency is a measure of how well an engine converts heat energy into mechanical work. It is expressed as a percentage and is calculated by dividing the amount of useful work produced by the engine by the total amount of heat energy supplied to the engine.

2. How is thermal efficiency determined?

Thermal efficiency is determined by measuring the amount of heat energy input and the amount of useful work output from the engine. This can be done using various instruments and calculations, such as the first and second law of thermodynamics.

3. What factors affect an engine's thermal efficiency?

There are several factors that can affect an engine's thermal efficiency, including the type of fuel used, the design and size of the engine, and the operating conditions (such as temperature and pressure). Additionally, regular maintenance and proper tuning can also impact an engine's thermal efficiency.

4. Why is thermal efficiency important?

Thermal efficiency is important because it indicates the effectiveness of an engine and its ability to convert energy into useful work. A higher thermal efficiency means that the engine is using its fuel more efficiently, resulting in better performance and potentially lower fuel consumption.

5. How can an engine's thermal efficiency be improved?

There are several ways to improve an engine's thermal efficiency, including using higher quality fuels, improving the design and size of the engine, optimizing the combustion process, and reducing heat loss through proper insulation. Regular maintenance and tuning can also help improve an engine's thermal efficiency.

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