Compression and Expansion Index

[EngNoob]

Could anyone tell me what the compression and expansion is used for in a Thermodynamics situation?

What is the notation for Compression and Expansion in a formula?

I am trying to calculate work done by a heat engine.

Thanks

 

[rohanprabhu]

Compression & Expansion basically relate to a change in Volume i.e. $\Delta V \ne 0$

Expansion is negative of Compression. Depending on your sign convention, either of them will be positive. Generally, $\Delta V$ is taken as $\Delta V = V_f - V_i$ and hence compression corresponds to a negative $\Delta V$ i.e. $-\Delta V_c > 0$

Also, if a conservative force is applied for either of the process, the work done for the same $|\Delta V|$ will have the same magnitude.

Under constant pressure, the work done in doing either of the process is given as:

$$W = P\Delta V$$

and for non-constant pressure, we express it in a differential equation. Note that here, Pressure will be some function of Volume and may also depend on Temperature which in turn maybe another function of Volume.

$$\int^{W}_0 dW = \int^{V_f}_{V_i}PdV$$

This holds only when there is no energy exchange from the system to the surrounding or vice versa in any form other than the force applied on the piston.

 

[sir-pinski]

for your question!

Compression and expansion are important concepts in thermodynamics that refer to changes in volume of a gas. In a thermodynamics situation, compression and expansion are used to describe the changes in volume of a gas as it undergoes a thermodynamic process. This can include changes in temperature, pressure, or both.

The compression index (k) and expansion index (n) are used to indicate the degree of compression or expansion in a gas. The compression index is used in isothermal compression, where the temperature remains constant, and the expansion index is used in isothermal expansion. These indices are typically represented in equations as subscripts, such as V1 and V2, indicating the initial and final volumes of the gas.

To calculate the work done by a heat engine, you can use the formula W = P(V2 - V1), where P is the pressure and V2 and V1 are the final and initial volumes, respectively. This formula takes into account the changes in volume (compression or expansion) that occur during the thermodynamic process.

I hope this helps clarify the concept of compression and expansion in thermodynamics and how it relates to calculating work done by a heat engine. Best of luck in your calculations!