Engineering Calculators / Gas–Liquid Separation
Demister Pad Gas Velocity & Area Estimator
Quick definition: Use a selected, project-supported Souders–Brown capacity factor (K) and operating gas/liquid densities to estimate a preliminary superficial gas velocity and required net exposed mist-eliminator area. This is a process-engineering screening calculation, not a pad performance guarantee.
Formula and interpretation
K-based superficial capacity velocity: vK = K × √[(ρL − ρG)/ρG]. Selected screening velocity: vdesign = vK × f, where f is the entered fraction from 0 to 1. Net required active flow area: A = Qactual / (3600 × vdesign) when Q is in m³/h. The equivalent unobstructed circular diameter is D = √(4A/π), before wall allowances, internals and supports.
If a known exposed cross-section is supplied, the tool also calculates its superficial operating velocity and the percentage of vK. Being below the selected capacity velocity alone does not establish droplet capture efficiency; low gas velocities may reduce inertial interception. Confirm the full minimum/normal/maximum turndown range.
Critical limitations: K depends on mesh style, thickness, density, liquid viscosity and surface tension, droplet-size distribution, liquid loading, flow orientation, drainage paths and vessel geometry. The simple equation does not predict dry/wet pressure drop, flooding, liquid re-entrainment, liquid carrying capacity, target micron droplet capture, liquid slugs or corrosion suitability. These require manufacturer/process engineering validation. Density inputs must represent actual operating conditions.
Worked arithmetic example
For 1,000 actual m³/h, gas density 1.2 kg/m³, liquid density 1,000 kg/m³, an illustrative user-selected K of 0.10 m/s and 80% design fraction: vK ≈ 2.885 m/s, vdesign ≈ 2.308 m/s, net required area ≈ 0.1203 m² and equivalent clear circular diameter ≈ 0.391 m. The K value is an arithmetic placeholder, not a product recommendation.
Frequently asked questions
Can I use standard gas flow directly?
No. Convert it to actual m³/h at the temperature and absolute pressure inside the pad using the Standard to Actual Gas Flow Calculator first.
Can the K factor be calculated from mesh density alone?
No. Different mesh constructions, orientation, liquid loading and drainage performance require distinct supported values. Do not infer K from bulk mesh density or porosity alone.
Does this calculator predict a 2–5 µm droplet removal efficiency?
No. It makes no size-specific separation efficiency claim. Obtain tested or validated performance data for the chosen pad style and duty.
Is calculated diameter the pad or vessel outside diameter?
No. It is the diameter of an ideal open circular flow area. Installation, seal, support grid, vessel clearance and allowable bypass need separate design and drawing checks.
Sources and next step
Engineering references: Koch-Glitsch — Mist Elimination and Phase Separations and Sulzer — Applying the Right Mist Elimination Physics. Consult the relevant full design and test data for K selection and performance acceptance. View our custom demister pad manufacturing options or Contact Our Engineers.