Ribbon blenders (U-trough with helical ribbons) are most suitable for homogeneous mixing of which type of materials?
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ALumpy solids and low-viscosity liquids
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BDry powders
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CHigh-viscosity liquids
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DThick pastes
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ESticky gums
Answer
Correct Answer: Dry powders
Explanation
Introduction / Context:Ribbon blenders are common in foods, chemicals, and pharmaceuticals. The counterflow motion of inner and outer ribbons promotes convective mixing in free-flowing bulk solids.
Given Data / Assumptions:
- Blender has a U-trough and a double-helix ribbon agitator.
- Target materials vary in flow properties.
Concept / Approach:Ribbon blenders excel with free-flowing dry powders and granules (e.g., flour, polymer pellets, additives). They provide reasonable mixing times and gentle handling with low power compared to high-shear mixers.
Step-by-Step Solution:Match mechanism (bulk conveyance) to material flowability.Select “Dry powders.”Exclude viscous/pasty feeds that require high-torque kneaders or planetary mixers.
Verification / Alternative check:OEM datasheets specify recommended bulk density and angle of repose ranges for effective ribbon mixing.
Why Other Options Are Wrong:High-viscosity/pastes/gums: need sigma-blade or double planetary mixers.Lumps with liquids: not ideal without pre-breaking and may smear.
Common Pitfalls:Overfilling the trough, which reduces mixing efficiency.
Final Answer:Dry powders