Background potential energy
= Background potential energy
{title2=$P_b$}
The background potential energy is the <gravitational potential energy> of the statically stable state obtained by adiabatically sorting a fluid's parcels. The difference $A=P-P_b$ is <available potential energy>. Pure rearrangement changes $A$ but not $P_b$; irreversible density mixing can increase $P_b$. Molecular exchange with <internal energy> must be separated when defining an irreversible mixing rate.