Fair’s Distillation Tray Flooding Velocity & Column Diameter Formula

Sizing sieve and valve distillation towers safely at 80% of James Fair’s jet-flooding ceiling!

If superficial vapor velocity inside a trayed distillation or absorption column rises too high, upward vapor jets carry liquid droplets onto the tray above (jet entrainment flooding), collapsing stage efficiency and spiking column ΔP! James R. Fair (Petro/Chem Engineer, 1961; Perry’s Chemical Engineers’ Handbook) extended Souders-Brown with a surface-tension droplet-breakup correction (σ_dyn_cm / 20)^0.2: u_flood = C_sb * SQRT((ρ_L - ρ_V) / ρ_V) * (σ / 20)^0.2 (m/s), where capacity parameter C_sb (typically 0.05–0.11 m/s) depends on tray spacing and flow parameter F_LV!

Size a hydrocarbon splitter with Fair capacity factor C_sb = 0.085 m/s, liquid density ρ_L = 780 kg/m^3, vapor density ρ_V = 2.60 kg/m^3, and surface tension σ = 16.5 dyn/cm (mN/m): jet flooding velocity u_flood = 1.414 m/s, giving a safe 80%-of-flood design velocity u_op = 1.131 m/s!

Fair Net-Area Vapor Flooding Velocity u_flood (m/s)

Computes C_sb * SQRT((ρ_L - ρ_V) / ρ_V) * (σ / 20)^0.2 across Fair capacity factor B2 (m/s), liquid density B3 (kg/m^3), vapor density B4 (kg/m^3), and surface tension B5 (mN/m = dyn/cm).

=IF(OR(B2 <= 0, B3 <= B4, B4 <= 0, B5 <= 0), "Invalid Tray Hydraulic Inputs", ROUND(B2 * SQRT((B3 - B4) / B4) * ((B5 / 20) ^ 0.2), 3))

Design Operating Vapor Velocity at Fractional Percent Flood (e.g., 80% Flood)

Multiplies u_flood by fractional flood factor B6 (0.80 = 80% of flooding).

=IF(OR(B2 <= 0, B3 <= B4, B4 <= 0, B5 <= 0, B6 <= 0, B6 >= 1), "Invalid Tray Hydraulic Inputs", ROUND(B6 * B2 * SQRT((B3 - B4) / B4) * ((B5 / 20) ^ 0.2), 3))

Further reading

• Microsoft Support — SQRT function