Packing geometry: the sphericity of a Raschig ring (length equal to its outside diameter) is expected to be

Introduction / Context:
Sphericity is a shape factor widely used in packed-bed calculations and particle technology. It compares a real particle’s surface-to-volume characteristics with those of a perfect sphere of the same volume.

Given Data / Assumptions:

• Sphericity, Φ = (surface area of sphere of equal volume) / (actual surface area of the particle).
• A perfect sphere has Φ = 1 by definition.
• A Raschig ring is a short, hollow cylinder whose length equals its outside diameter.

Concept / Approach:
Non-spherical particles expose more surface area per unit volume compared with a sphere. Since Φ uses the ratio of the smaller spherical area to the larger actual area, Φ for elongated, flaked, or hollow shapes is less than one. Random packings like Raschig rings therefore have Φ < 1.

Step-by-Step Solution:
Recognize definition: Φ = A_sphere / A_actual.For ring or cylinder segments, A_actual > A_sphere at same volume.Hence Φ < 1.

Verification / Alternative check:
Tabulated sphericities for cylinders, rings, and saddles are typically in the 0.3–0.9 range, always below unity.

Why Other Options Are Wrong:
Φ > 1 or Φ = 2 is impossible with this definition; no real particle has less actual area than the equal-volume sphere.Φ = 1 applies only to perfect spheres.

Common Pitfalls:
Confusing sphericity with roundness or aspect ratio; sphericity is a precise surface/volume-based metric, not a visual descriptor.

Final Answer:
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