Industrial mixing — paddle agitators:\nSelect the typical speed range (revolutions per minute) for industrial paddle agitators used for low-to-medium viscosity fluids.

Introduction / Context:
Paddle agitators are radial-flow, low-shear impellers suited to blending, solid suspension (with limitations), and heat transfer in tanks where gentle circulation is preferred. Their operating speeds are much lower than those of high-shear impellers like turbines.

Given Data / Assumptions:

• Standard tank sizes in typical chemical plants.
• Newtonian or mildly non-Newtonian fluids of low-to-medium viscosity.
• Electric motor with gearbox or VFD speed control.

Concept / Approach:
Power draw and flow regime depend on tip speed and Reynolds number. Paddle impellers trade shear for broad circulation, so they typically operate in tens of rpm, not hundreds or thousands.

Step-by-Step Reasoning:

Verification / Alternative check:
Vendor datasheets and mixing handbooks list paddle ranges typically starting near 20 rpm and topping near 100–150 rpm depending on duty.

Why Other Options Are Wrong:

• 1–5 rpm or 5–10 rpm: too low for effective bulk circulation in most sizes.
• 500–750 rpm and 1000–2000 rpm: characteristic of smaller high-shear impellers (e.g., Rushton turbines), not paddles in production tanks.

Common Pitfalls:
Assuming “faster is better”; excessive rpm increases vortexing and power without proportional mixing benefits for paddles.

Final Answer:
20 to 100 rpm