Thanks in advance, I wants to understand the concept and not just know the equations!
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Since the question is tagged “Physics” I’ll tackle that side of the problem.
Suppose you have some fluid in a box. You can measure its temperature (T), pressure (P), and volume (V). From those you can determinete its internal energy (U). As its name says, U is a measure of the energy of the fluid in its current state.
You can increase U by heating up the box (heat flow toward the fluid) and/or compressing the box (applying work to the fluid); and you can decrease U by cooling down the box (heat flow from the fluid) and/or letting the box expand (the fluid does work toward the environment).
But, for many practical applications, your fluid is not in a box, but it is flowing through a pipe or going throug a machine (think a pump, a turbine, a radiator, etc). You can still measure T and P for the fluid, and if you consider a fixed lenght of pipe you can still measure its volume, though it is generelly more useful to think in terms of density (d), as in d = volume / mass.
You can also still consider U, but once again it is not that useful. Since the fluid is in motion, it is constantly entering and exiting your volume, which creates an additional energy called Pulsion Work.
I am not talking about kinetic energy, which depends on the velocity of the fluid, that is a separate term.
This pulsion work is calculated as P * V. So if you managed to determinate U, you can also determinate the Pulsion Work. Given that it depends on the same properties as U, and that it is more significative for flowing systems, the Enthalpy (H) was defined as H = U + P * V.
I hope this helps.
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