A reversible polytropic process can be described by
PVn = constant
Polytropic Process Overview
In thermodynamics, a polytropic process is a generalized thermodynamic process that can be used to describe many different types of processes, including isobaric, isochoric, isothermal, and adiabatic processes.
Polytropic Process Definition
A polytropic process is defined by a simple mathematical relationship between pressure (P) and volume (V). For a reversible polytropic process, this relationship is expressed by the equation:
\[PV^n = \text{constant}\]
Let's break down the components of this equation:
- \(P\): Represents the absolute pressure of the gas or system.
- \(V\): Represents the volume of the gas or system.
- \(n\): Is known as the polytropic index or exponent. This value can be any real number and determines the specific type of thermodynamic process.
- \( \text{constant}\): Indicates that the product \(PV^n\) remains unchanged throughout the process.
Polytropic Index Significance
The value of the polytropic index, \(n\), is crucial as it dictates the characteristics of the process. Different values of \(n\) correspond to specific common thermodynamic processes:
| Value of \(n\) | Type of Process | Equation Form |
|---|---|---|
| \(n = 0\) | Isobaric Process (Constant Pressure) | \(P = \text{constant}\) |
| \(n = 1\) | Isothermal Process (Constant Temperature) | \(PV = \text{constant}\) |
| \(n = \gamma\) (ratio of specific heats, \(C_p/C_v\)) | Adiabatic Process (No Heat Transfer) | \(PV^\gamma = \text{constant}\) |
| \(n = \infty\) | Isochoric Process (Constant Volume) | \(V = \text{constant}\) |
This flexibility makes the polytropic process equation a powerful tool for analyzing various thermodynamic systems.
Reversible Polytropic Process Equation
The question specifically asks for the description of a reversible polytropic process. The equation \(PV^n = \text{constant}\) accurately describes such a process. A reversible process is an idealized process that can be reversed without leaving any trace on the surroundings, often implying slow, quasi-static changes and no dissipative effects like friction.
Therefore, among the given options, the equation \(PV^n = \text{constant}\) correctly represents a reversible polytropic process.
Important Questions from Thermodynamics System and Processes
Select the right expression for Vander Waal’s equation for a real gas.
Which of the following pairs of thermodynamic properties can uniquely fix the state of a substance like water, irrespective of its thermodynamic state?
A Monoatomic ideal gas (y = 1.67 Molecular weight = 40) is compressed adiabatically from 0.1 Mpa 300K to 0.2Mpa. The universal gas constant is 8.314KJ/kgK. The work of the compression of gas in KJ/kg is. (Take (2)y-1/y = 1.32)
A gas goes through a process given by pv2 = c. It expands from state 1 of 350 kPa and 0.049 m3 to a final pressure of 150 kPa. Work delivered during this process in kJ is:
The pressure inside a balloon is proportional to the square of its diameter. It contains 2 kg of water at 150 kPa with 85% quality. The balloon and water are now heated so that a final pressure of 600 kPa is reached. The process undergone by the water is given by p-v equation as:
