Fluid_Aspect_Course_2_2_5

Fluid Aspect Course 2.2.5: Entropy & Internal Energy

These are fluid state properties that are not modeled in GUNNS, and the ramifications of omitting them.

Internal Energy

GUNNS neglects to model the fluid internal energy because simplifications in the enthalpy negate the need for it.

h = U + pV

We neglect the pV term and then h = U. This is valid for all fluid phases up to about 1000 atmospheres or ~7350 psi (at 10% error), which is about as high pressure as we ever go.

Most heat transfers happen at near-constant pressure, so the difference in the enthalpy errors at the inlet & exit pressures of the process is small and introduces negligible error in heat transfer.

Entropy

GUNNS neglects to model the fluid entropy because isentropic flow relations for ideal gas are good at modeling constant-entropy processes without needing an entropy term.

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