Minimum Reflux Ratio Calculator

Minimum Reflux Ratio Formula

Worked Example

A saturated-liquid feed at 50 % with α = 2.5 and 95 % distillate:

1. Solve αx_F/(α − θ) + (1 − x_F)/(1 − θ) = 1 − q for 1 < θ < α → θ = 1.428571429
2. R_min + 1 = αx_D/(α − θ) + (1 − x_D)/(1 − θ) → R_min = 1.1

Typical operating reflux 1.2–1.5 R_min: 1.65

GATE tip

For a saturated liquid feed, the pinch is at x = x_F: R_min = (x_D − y*)/(y* − x_F) with y* from the equilibrium curve.

More Mass Transfer Calculators

• Fenske Equation Calculator

  N_min = ln[(x_D/(1 − x_D))((1 − x_B)/x_B)] / ln α

  N_min includes the reboiler as a stage

  Example: Separating to 95 % and 5 % with α = 2.5: Minimum number of stages N_min = 6.42687.

  Open the fenske equation calculator →

• Kremser Equation Calculator

  N = ln[((y_N+1 − mx₀)/(y₁ − mx₀))(1 − 1/A) + 1/A] / ln A

  A = L/(mV); N = (y_N+1 − y₁)/(y₁ − mx₀) when A = 1

  Example: Absorbing a gas from 5 % to 0.5 % with pure solvent, m = 1.2 and L/V = 1.8: Number of ideal stages N = 3.41902.

  Open the kremser equation calculator →

• Fick’s Law Calculator

  N_A = (D_AB P / RTz) ln[(P − p_A2)/(P − p_A1)]

  equimolar: N_A = D_AB (p_A1 − p_A2)/(RTz)

  Example: Water evaporating at 25 °C through 10 mm of still air (D = 0.26 cm²/s): Molar flux N_A = 0.00337961 mol/(m²·s).

  Open the fick’s law calculator →

• Evaporator Calculator

  S λ_s = F c_p (T₁ − T_F) + V λ

  P = F x_F/x_P, V = F − P, economy = V/S, A = Q/(U ΔT)

  Example: 10,000 kg/h of 5 % solution fed at 25 °C, concentrated to 25 % at 100 °C with 120 °C steam: Steam required S = 9562.22 kg/h.

  Open the evaporator calculator →

Frequently asked questions

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.