Thermal Efficiency and Heat Extraction in Heat Engines: Figure Analysis

In summary, the thermal efficiency for the heat engine shown in the figure is 40/320, or 12.5%. The heat extracted from the hot reservoir is 320J and the heat leaving the engine is 280J. The formula for efficiency is Wout/Qh.
  • #1
Ravey
5
0
1. What is the thermal efficiency for the heat engine shown in the figure?
What is the heat extracted from the hot reservoir for the heat engine shown in the figure?t

Figure shown here:
knight_Figure_19_16.jpg




2.Wout = 1/2 B*H Also, Qc=Qh-Wout, efficiency: Wout/Qh



3. Wout = .5 * 200KPA* (400x10^-6m^3). I have no idea how to obtain Qc (cold reservoir) or Qh (hot)
 
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  • #2
Hi Ravey, welcome to PF. What's the significance of the heat flows marked on the image?
 
  • #3
Thanks!

I believe that is heat leaving the engine*, but what do I do? Add them? According to some note Qc is the sum of the heat leaving the engine. So I assume so. However, qh is not 280-40 = 240. What's going wrong?
 
Last edited:
  • #4
Stumped too I see ;)
 
  • #5
Hint: No energy is stored in the engine from cycle to cycle.
 
  • #6
Got it!


Qh=Q_c+W_out = 280J + 40J = 320J.

40/320 = efficiency.
 
  • #7
Sounds good!
 

Related to Thermal Efficiency and Heat Extraction in Heat Engines: Figure Analysis

1. What is a heat engine?

A heat engine is a device that converts thermal energy into mechanical energy, which can then be used to do work. This process is governed by the laws of thermodynamics.

2. How does a heat engine work?

A heat engine works by utilizing a heat source, such as burning fuel or steam, to produce mechanical work. This is achieved through the use of pistons, turbines, or other mechanical components that convert the heat energy into rotational motion.

3. What are the different types of heat engines?

There are several types of heat engines, including steam engines, internal combustion engines, Stirling engines, and gas turbines. Each type operates in a slightly different way and has its own advantages and disadvantages.

4. What is the efficiency of a heat engine?

The efficiency of a heat engine is a measure of how well it converts thermal energy into mechanical work. It is typically expressed as a percentage and is governed by the laws of thermodynamics. The maximum possible efficiency for a heat engine is given by the Carnot efficiency.

5. How are heat engines used in everyday life?

Heat engines are used in a wide variety of applications in everyday life, such as in cars, power plants, and household appliances. They are also used in industrial processes, such as refrigeration, air conditioning, and manufacturing. Without heat engines, many of the modern conveniences we rely on would not be possible.

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