For a multiple-blade paddle agitator handling high-viscosity liquids or pastes, the paddle diameter is about 0.8 of the tank diameter. What is the usual range for blade width expressed as a fraction of paddle diameter?

Introduction / Context:
Paddle agitators are workhorses for viscous mixing in reactors, crystallisers, and paste kettles. Geometry—diameter, blade width, and clearance—directly impacts power draw, flow pattern, and shear. A standard design parameter is the blade width as a fraction of paddle diameter.

Given Data / Assumptions:

• Paddle diameter D_p ≈ 0.8 D_tank.
• High-viscosity or paste-like fluids; laminar to transitional regimes.
• Multiple-blade paddle with flat blades.

Concept / Approach:
For viscous mixing, broad blades can increase drag excessively without proportionate mixing benefits, while very narrow blades may not produce sufficient bulk motion. Empirical correlations and standard design guides converge on a moderate width range to balance torque and circulation.

Step-by-Step Solution:

Verification / Alternative check:
Design handbooks consistently show blade width between one-tenth and one-quarter of D_p for paddles, with blade count and baffling tailored to rheology.

Why Other Options Are Wrong:

• 0.30–0.50 and larger: Usually excessive, increasing torque without commensurate flow improvement.
• 0.02–0.05: Too narrow to move viscous masses effectively, causing poor turnover.

Common Pitfalls:
Omitting baffles in viscous mixing (leading to vortexing) or oversizing blade width, which can overload drives and shafts.

Final Answer:
0.10 to 0.25 of paddle diameter