Regarding particle shape, what is the typical sphericity value for pulverised coal particles used in combustion systems?

Introduction / Context:Sphericity (ψ) compares the surface area of a sphere with the same volume to the actual particle surface area. Real fragmented particles are irregular, influencing drag, settling, and combustion behavior.

Given Data / Assumptions:

• Pulverised coal results from mechanical grinding.
• Particles are angular/irregular rather than perfectly spherical.

Concept / Approach:A perfect sphere has ψ = 1. Irregular particles have greater surface area than a sphere of equal volume, so ψ < 1. Pulverised coal commonly exhibits ψ appreciably below unity, affecting aerodynamic and combustion characteristics (e.g., higher drag, quicker burnout due to higher specific surface).

Step-by-Step Solution:Define sphericity.Relate irregularity to increased surface area.Conclude ψ < 1 for pulverised coal.

Verification / Alternative check:Measured shape factors for milled coals in literature typically lie below 1, consistent with fragmented solids.

Why Other Options Are Wrong:=1 implies perfect spheres; >1 is impossible by definition; ∞/0 are nonphysical here.

Common Pitfalls:Assuming atomized liquids (nearly spherical droplets) when dealing with crushed solids.

Final Answer:<1