Confusion over Thermodynamic process (heat and termperature)

In summary, the Carnot and Rankine Cycles involve four processes - 4-1, 1-2, 2-3, and 3-4 - that are represented by straight horizontal lines on a T-s diagram. While the temperature remains constant during processes 4-1 and 2-3, heat transfer in the form of latent heat occurs, causing a change in phase of the fluid. This explains why the temperature does not increase or decrease during these processes. However, in the Rankine cycle, there is also a sensible heat gain during process 4-1, which can be seen in a modified Rankine cycle as superheat.
  • #1
skaboy607
108
0
Hi

I have been learning about the Carnot and Rankine Cycles, where process 4-1 is through a evaporator, process 1-2 a turbine, 2-3 a condensor and 3-4 a compressor. Sketching this on a T-s diagram gives straight horizontal lines for processes 4-1 and 2-3. This is where the heat is extracted and put in, so I don't understand how temperature does not increase and decrease. i.e, you add heat in the form of flame to water and its temperature increases. Probably simple but it has been driving me crazy!

Any help would be most appreciated.

Thanks
 
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  • #2
If the water is at 100 C and atmospheric pressure and you add a flame to it, what happens to the temperature?
 
  • #3
You are neglecting the phase change of the water. The heat being put into and removed from the fluid is in the form of latent heat. So the temperature remains constant but the fluid changes phase. Since you have heat transfer at a temperature, you have entropy creation or removal, hence the strait horizontal line.
 
  • #4
skaboy607 said:
Sketching this on a T-s diagram gives straight horizontal lines for processes 4-1 and 2-3.

does so for carnot cycle, doesmt for rankine cycle. Rankine cycle also has a sensible heat gain part in the process 4-1(considering 4 is the pump outlet). If you have seen a modified rankine cycle, it has a sensible heat gain after the total evaporation(& its called superheat)
 

1. What is the difference between heat and temperature in a thermodynamic process?

Heat and temperature are often used interchangeably, but they are actually two different concepts in a thermodynamic process. Heat is a form of energy that is transferred from a hotter object to a cooler object. Temperature, on the other hand, is a measure of the average kinetic energy of the particles in a substance. In other words, heat is the transfer of energy, while temperature is a measure of the intensity of that energy.

2. How are heat and temperature related in a thermodynamic process?

In a thermodynamic process, heat and temperature are related through the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred or converted. This means that when heat is transferred to a substance, the temperature of that substance will increase. Similarly, when heat is removed from a substance, the temperature will decrease.

3. Why is there confusion over the terms heat and temperature in thermodynamics?

There is often confusion between the terms heat and temperature in thermodynamics because they are closely related, but they are not the same thing. In everyday language, these terms are often used interchangeably, but in the field of thermodynamics, they have specific definitions and meanings.

4. Can heat flow from a colder object to a hotter object in a thermodynamic process?

No, heat cannot flow from a colder object to a hotter object in a thermodynamic process. This is because heat always flows from a higher temperature to a lower temperature. This is a fundamental principle of thermodynamics known as the second law of thermodynamics.

5. How does the concept of entropy relate to confusion over heat and temperature in thermodynamics?

The concept of entropy, which is a measure of the disorder of a system, can also contribute to confusion over heat and temperature in thermodynamics. This is because heat transfer can increase the entropy of a system, making it more disordered, while a change in temperature may not necessarily have the same effect. Therefore, it is important to understand the difference between heat and temperature in order to fully grasp the concept of entropy in thermodynamics.

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