This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Paddle”.
1. Which of the following type of paddle agitators are most commonly used?
a) Two Bladed
b) Three Bladed
c) Four Bladed
d) Two bladed and four bladed
View Answer
Explanation: Both two bladed and four bladed paddle agitators are most commonly used in the chemical industry as it provides uniformity and homogeneity in agitation operation.
2. In some designs the blades conform to the shape of a dished or a hemi-spherical vessel.
a) True
b) False
View Answer
Explanation: In some designs the blades conform to the shape of a dished or a hemi-spherical vessel so that they scrape the surface or pass over it with close clearance. A paddle of this kind is known as anchor agitator.
3. Anchor agitator is recommended for higher-viscosity operations.
a) False
b) True
View Answer
Explanation: Two-bladed anchors are for use in blending and heat transfer, with viscosities from 10,000 to 100,000 centipoises. Anchor agitators are available in several configurations for use with moderate to high viscosity materials.
4. Which of the following is not an application of paddle agitator?
a) Mixing ingredients in cooking
b) Mixing ingredients for construction products, such as pastes, slurries or paints
c) Dispersing solids within liquids
d) Mixing low viscosity liquids
View Answer
Explanation: Various applications of a paddle agitator are mixing of ingredients in cooking, mixing ingredients for construction products, such as pastes, slurries or paints, dispersing solids with liquids, pigmenting caulking or paint with powder additives.
5. Which of the following is/are examples of paddle agitators?
a) Grout agitator
b) Turbine agitator
c) Hydrostatic agitators
d) Propeller agitator
View Answer
Explanation: Some of the examples of paddle agitators are mudwhip agitator, grout agitators, anchor agitators and many others. Grout agitators are used to slowly stir the materials and prevent separation. The agitators are designed with a vertical shaft and feature specially designed blades and baffles to bring out gentle mixing action.
6. Paddle agitators are used to maintain which of the following flow pattern?
a) Laminar
b) Turbulent
c) Intermediate
d) Non-uniform
View Answer
Explanation: Paddle agitators are used where a uniform laminar flow of liquids is desired which is provided by the help of long paddles which provide uniform mixing and homogeneity in the process.
7. Which of the following agitator is commonly used in reactors?
a) Anchor agitator
b) Paddle agitator
c) Radial propeller agitator
d) Turbine agitator
View Answer
Explanation: Anchor agitator is generally used in reactors because the anchor impeller is the most economical laminar flow impeller, and by the perspective of the industry this is the biggest advantage. It is most effective in slurry-like batches where vertical pumping is not that important.
8. Which of the following is a feature of anchor agitator?
a) Most economical laminar flow impeller available
b) Vertical flow well-suited for low liquid level geometries
c) Solve mass transfer problems with optional wall scrapers
d) High liquid level geometries
View Answer
Explanation: Anchor agitator has various features like; it is most economical laminar flow impeller, it has horizontal flow which is well suited for low liquid level geometries, the upright length can be varied, Teflon wipers can be mounted on the anchor to provide complete tank mixing.
9. Anchor agitator operates at low rpm.
a) True
b) False
View Answer
Explanation: It is true that anchor agitator is operated at low rpm. Anchor agitators are usually used for operations at relatively slow speeds and generally require a heavy system which is capable of generation and giving required torque to the agitator.
10. What is the range of time required for standard mixing applications?
a) Between 1 and 3 minutes
b) Between 5 and 10 minutes
c) Between 3 and 5 minutes
d) Between 10 and 15 minutes
View Answer
Explanation: The mixing time depends on the process that we are using and the characteristics of products in our process. For standard mixing processes the mixing time lies between 3 to 5 minutes.
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