Sieve (seive) tray drilling practice: the normal hole pitch is what multiple of the hole diameter to achieve the desired open area?

Introduction / Context:
Sieve trays control vapor distribution through the liquid on a tray using a grid of perforations. The open area and the geometric pitch-to-diameter ratio drive vapor velocity through holes, weeping tendency, pressure drop, and overall contacting efficiency. Designers commonly use standardized multiples of hole diameter for layout convenience and repeatable hydraulics.

Given Data / Assumptions:

• Hole sizes from about 2.5 to 12 mm are typical; 5 mm is a widely used baseline.
• We assume non-foaming or mildly foaming systems under typical refinery/petrochemical conditions.

Concept / Approach:
The pitch must be large enough to maintain mechanical strength and proper ligament while providing sufficient open area. Empirical practice converges around a pitch between 2.5 and 4.0 times the hole diameter for common services. This achieves a target open fraction while preserving tray rigidity and manageable pressure drop.

Step-by-Step Solution:

Verification / Alternative check:
Vendor design manuals present similar guidance to hit open areas often in the range of roughly 8–12% for sieve trays, depending on duty and hydraulics.

Why Other Options Are Wrong:

• 0.5–1.5: Too tight; insufficient ligament and likely structural weakness.
• 5–10 or 10–15: Too wide; open area becomes too low for common vapor rates, risking weeping and low capacity.

Common Pitfalls:
Focusing only on percent open area without checking tray stiffness, downcomer design, and weir loading; ignoring fouling propensity which may require larger holes or altered pitch.

Final Answer:
2.5 to 4.0 times the hole diameter