Underwood Equations

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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.

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Underwood Equations (L/D)min
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1st Underwood Equation f Roots
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Underwood Equations Cases
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Underwood Equations Case A Methodology
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Underwood Equations Case A Methodology
(continued)
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Underwood Equations Case A Methodology
(continued)
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Underwood Equations Case B Methodology
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Underwood Equations Case B Methodology
(continued)
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Underwood Equations Case B Methodology
(continued)
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Underwood Equations Case C Methodology
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Underwood Equations Case C Methodology
(continued)
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Underwood Equations Case C Methodology
(continued)
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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.

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Gilliland Correlation
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Gilliland Correlation Curve Fits
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Gilliland Correlation NF