This equation with a value of 150 instead of 180 is called the Ergun equation and is simply the sum of Eqs (13-15) and (13-16). (The more recent references favor the value of 180, which is also more conservative.) Obviously, for NRe;PM < 10 the first term is small relative to the second, and the Ergun equation reduces to the Blake-Kozeny equation. Likewise, for NRe;PM > 1000 the first term is much larger than the second, and the equation reduces to the Burke-Plummer equation.

If the definitions of fPM and NRe;PM are inserted into the Ergun equation, the resulting expression for the frictional energy loss (dissipation) per unit mass of fluid in the medium is

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