Polytropic Processes: Reversible vs Irreversible

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In summary, polytropic processes are characterized by pvn = constant and are valid for both reversible and irreversible processes, depending on the specific conditions. The relationship PV=nRT applies to all isothermal processes, while the adiabatic condition PV^γ = K only applies to reversible adiabatic changes. For processes with heat flow and a non-constant temperature, the polytropic index may fall within the range of 1 < n < γ, and the process can still be characterized by pvn = constant if it is reversible. However, for processes with irreversibility, such as friction, the characterization of the process becomes more complex and may require additional considerations.
  • #1
jason.bourne
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polytropic processes are characterized by pvn = constant.

are they valid for both reversible as well as irreversible processes?
 
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  • #2
jason.bourne said:
polytropic processes are characterized by pvn = constant.

are they valid for both reversible as well as irreversible processes?
It depends.

The relationship PV= constant (ie n = 1) for an ideal gas applies for all isothermal processes, reversible or non-reversible (ie. PV=nRT)

However, the adiabatic condition for an ideal gas:

[itex]PV^\gamma = K[/itex] applies only to a reversible adiabatic change.

AM
 
  • #3
thanks Andrew.

suppose if there is a process in which heat flow is happening and the temperature of the system is not constant, let's assume that polytropic index is in the range 1 < n < γ.

if the process was reversible, then it is reversible polytropic process and we can characterize it by pvn = constant.

but what if there was friction or some other sort of irreversibility?
how do we take that into account? how can we characterize such polytropic processes?
 

1. What is a polytropic process?

A polytropic process is a thermodynamic process in which the relationship between pressure and volume can be described by the equation P*V^n=constant, where P is pressure, V is volume, and n is a constant. This equation is also known as the polytropic equation.

2. What is the difference between a reversible and irreversible polytropic process?

A reversible polytropic process is one in which the system can be returned to its original state by reversing the steps of the process. This means that the process is infinitely slow and does not result in any energy loss. An irreversible polytropic process, on the other hand, cannot be reversed and always results in some energy loss in the form of heat.

3. How can we determine if a polytropic process is reversible or irreversible?

The reversibility of a polytropic process can be determined by examining the entropy change of the system. If the entropy change is zero, the process is reversible. If the entropy change is positive, the process is irreversible.

4. What are some examples of polytropic processes?

A common example of a polytropic process is the expansion and compression of a gas in a cylinder. Other examples include adiabatic processes in a closed system and the compression or expansion of fluids in a pump or turbine.

5. What is the significance of polytropic processes in thermodynamics?

Polytropic processes are important in thermodynamics because they allow us to analyze and understand the behavior of systems undergoing changes in pressure and volume. They also provide a way to determine the work and heat transfer associated with these processes, which is essential in many engineering applications.

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