Underwood Equations – (L/D)min We have looked at one limiting condition, Nmin, determined using the Fenske method at total reflux conditions. The other limiting condition for multi-component systems is the solution for the minimum reflux ratio, (L/D)min, which gives us an infinite number of stages. This method is known as the Underwood method or the Underwood equations. Lecture 18

Underwood Equations – (L/D)min Lecture 18

1st Underwood Equation – φ Roots Lecture 18

Underwood Equations – Cases Lecture 18

Underwood Equations – Case A Methodology Lecture 18

Underwood Equations – Case A Methodology (continued) Lecture 18

Underwood Equations – Case A Methodology (continued) Lecture 18

Underwood Equations – Case B Methodology Lecture 18

Underwood Equations – Case B Methodology (continued) Lecture 18

Underwood Equations – Case B Methodology (continued) Lecture 18

Underwood Equations – Case C Methodology Lecture 18

Underwood Equations – Case C Methodology (continued) Lecture 18

Underwood Equations – Case C Methodology (continued) Lecture 18

Gilliland Correlation – N and NF Empirical relationship which relates the number of stages, N, at finite reflux ratio, (L/D)actual to the Nmin and (L/D)min. Nmin is determined from the Fenske equation. (L/D)min is determined from the Underwood equations. Lecture 18

Gilliland Correlation Lecture 18

Gilliland Correlation – Curve Fits Lecture 18

Gilliland Correlation – NF Lecture 18