Demister pad selector
Size a knitted-mesh mist eliminator from vessel diameter, gas velocity and densities. Returns the Souders–Brown limit, pad density, thickness, wire diameter and the material the service actually needs.
How the sizing works
- What is the Souders–Brown equation?
- It sets the maximum gas velocity a mist eliminator can handle: V_max = K × √((ρ_liquid − ρ_gas) / ρ_gas). K is an empirical capacity factor — about 0.107 m/s for a horizontal pad in vertical flow. Operate below V_max and the pad separates; above it, liquid re-entrains and carries over.
- Why does the K factor change with service?
- K is calibrated for clean, standard conditions. A vertical pad in horizontal flow has less effective capture area, so K drops by roughly a quarter. Vacuum service, fouling duty and vessel motion all reduce it further. The selector applies these as multipliers on the base figure.
- Why 85% rather than 100% of maximum velocity?
- Because V_max is the point at which the pad floods, not a target. Process conditions swing, and a design sitting at 98% will carry over the first time throughput rises. Standard practice is to leave margin — the gauge marks 85% as the design limit.
- Why does a larger vessel fix flooding?
- Velocity through the pad is volumetric flow divided by cross-sectional area, and area goes with the square of diameter. Increasing the vessel diameter therefore drops velocity sharply. When the selector detects flooding it calculates the diameter that brings loading back to 80%.
- Can I rely on this for final design?
- No — it is indicative sizing for preliminary engineering. The K factors are empirical and the pressure drop is an estimate rather than a vendor curve. Send us your process data sheet and we will review the selection properly.