Polytropic Processes: Reversible vs Irreversible

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SUMMARY

Polytropic processes are defined by the equation pVn = constant, applicable to both reversible and irreversible processes under specific conditions. For ideal gases, the isothermal process follows the relationship PV = nRT, valid for both reversible and non-reversible scenarios. However, the adiabatic condition, represented as PVγ = K, is exclusive to reversible adiabatic changes. In cases where the polytropic index n falls between 1 and γ, the process can be characterized as a reversible polytropic process, but the presence of friction or other irreversibilities complicates this characterization.

PREREQUISITES
  • Understanding of polytropic processes and the equation pVn = constant
  • Knowledge of ideal gas laws, specifically PV = nRT
  • Familiarity with adiabatic processes and the equation PVγ = K
  • Basic thermodynamics concepts, including reversibility and irreversibility
NEXT STEPS
  • Study the implications of the polytropic index in thermodynamic processes
  • Explore the differences between reversible and irreversible adiabatic processes
  • Investigate the effects of friction on thermodynamic systems
  • Learn about real gas behavior and deviations from ideal gas laws
USEFUL FOR

Students and professionals in thermodynamics, mechanical engineers, and anyone studying the principles of energy transfer and process efficiency in thermodynamic systems.

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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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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:

PV^\gamma = K applies only to a reversible adiabatic change.

AM
 
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?
 

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