Mass-transfer equipment — On sieve trays, the perforations (holes) are commonly laid out on a triangular pitch equal to how many times the hole diameter?

Introduction:
Sieve tray hydraulics depend strongly on hole size, pitch, fractional open area, and weir/downcomer layout. Triangular pitch improves vapour dispersion and tray rigidity while controlling the open area to prevent weeping and minimise pressure drop.

Given Data / Assumptions:

• Conventional sieve trays with typical hydrocarbon service.
• Hole diameters often 3–8 mm (about 1/8–5/16 in).
• Need a practical pitch range used in industry.

Concept / Approach:
The triangular pitch is usually a few multiples of the hole diameter to achieve an open area roughly 6–15% of the active tray area. Too close a pitch increases open area (risking weeping); too wide a pitch limits vapour distribution and capacity. The common design range is 2.5–5 times the hole diameter.

Step-by-Step Solution:
Relate pitch to desired fractional open area and structural spacing.Select the standard design guidance: triangular pitch ≈ 2.5–5 × hole diameter.Verify that this yields reasonable open area (≈6–15%).

Verification / Alternative check:
Vendor practices and tray handbooks list triangular pitch multiples in this range for common services and hole sizes.

Why Other Options Are Wrong:

• 1.5–2: pitch too tight, open area often excessive.
• 5–10 or 10–15: pitch too wide, risking maldistribution and limited capacity.

Common Pitfalls:
Ignoring fouling tendency which may motivate slightly larger holes or pitch; neglecting the interaction with weir height and froth regime.

Final Answer:
2.5 to 5