Standard sieve conversion (200 mesh)\nOn the standard sieve scale used in process engineering, a 200-mesh sieve corresponds to approximately how many micrometres (µm)?

Introduction / Context:
Mesh numbers are ubiquitous in lab work (sieving), quality control, and equipment specification. Converting between mesh and metric opening (micrometres) is essential for comparing to particle size analyzer outputs or setting cut points for classifiers and filters.

Given Data / Assumptions:

• Standard 200 mesh means roughly 200 openings per linear inch in the sieve cloth.
• Use of standard tables that account for wire diameter and series (Tyler/ASTM), giving 200 mesh ≈ 74 µm nominal opening.

Concept / Approach:
While a crude inverse of count per inch (25.4 mm/in divided by 200) gives 127 µm, standard sieves use specific wire diameters that reduce the open space. Thus, the accepted nominal aperture for 200 mesh in standard practice is 74 µm. This value is widely used for defining fine product specifications (e.g., “80% passing 200 mesh”).

Step-by-Step Solution:

Verification / Alternative check:
Handbooks and ASTM E11 tables list 200 mesh openings at approximately 0.074 mm (that is 74 µm), confirming the selection.

Why Other Options Are Wrong:

• 24 µm and 47 µm: too fine for 200 mesh; nearer to 500–325 mesh apertures.
• 154 µm or 200 µm: too coarse; align with meshes closer to 100 and 70.

Common Pitfalls:
Ignoring the role of wire diameter and relying only on 25.4/mm count; always consult standardized tables for nominal openings.

Final Answer:
74