# Learn: Thermodynamics

## Ideal Gas Law

The ideal gas law defines the properties of a gas assuming it behaves ideally. For most cases, gases behave close enough to ideal that the ideal gas law can be employed to predict its behaviour with little error. The ideal gas law defines the relationship between a gas' pressure $P$ (Pa), the volume it occupies $V$ (m$^3$)and its temperature $T$ (K):

## Steady flow energy equation

For a steady flow through a control volume with a single inlet and single outlet, the energy equation can be written as:

$\dot{Q} - \dot{W}_s -\dot{W}_v = \dot{m}\left[(h_2 + \frac{1}{2}v_2^2 + gz_2) - (h_1 + \frac{1}{2}v_1^2 + gz_1)\right]$

## Enthalpy

Enthalpy, $H$ (kJ) is a measure of the total heat content of a system. It is defined as the system's internal energy $U$ (kJ) plus the product of the pressure $p$ (N/m$^2$) times volume $V$ ($m^3$):

$H = U + pV$

Because the $U + pV$ appears frequently in engineering calculations, the combination is given the name enthalpy. The enthalpy is the system's potential energy.

It's common to discuss the properties of fluids in terms of per unit mass: