Mechanical Operations Multiple Choice Questions on “Static Mixers”.
1. Which of the following are properties of an ideal static mixer?
a) Enables ideal mixing at the lowest pressure drop, for lowest installed cost
b) Enables ideal mixing at the highest pressure drop, for lowest installed cost
c) Enables ideal mixing at the highest pressure drop, for lowest installed cost and compact
d) Enables ideal mixing at the lowest pressure drop, for lowest installed cost and compact
Answer: d
Clarification: A static mixer is designed using appropriate design parameters such as length and diameter. This ensures the right size for the mixer to fit the available space. It must mix corresponding to the least pressure drop possible. Meanwhile, installation and maintenance costs should be low.
2. Which of the following is true about the use of baffles in static mixers?
a) They move streams axially
b) Baffles have high degree of backflow
c) Baffles can only be parallel bars
d) Baffles functioning is design dependent
Answer: d
Clarification: Streams are moved radially by a series of metal baffles. These baffles may be metal twists, sheets, parallel bars, or tabs sticking out from the wall. They have a small degree of back mixing and not high. Baffles are dependent on the exact design of the static mixer, therefore, not every static mixer can have the same baffles.
3. Which of the following is correct about static mixers during turbulent flow?
a) There is relatively more pressure drop in turbulent conditions
b) Number of static mixers are not dependent on viscosity
c) Static mixers are not limited by length
d) Turbulent shear is applied efficiently to the additive liquid or gas to create a dispersion or droplets or bubbles
Answer: d
Clarification: In turbulent conditions, mixing can be achieved with 4 or 6 elements and a relatively minor loss in pressure. The number of static mixer elements vary greatly with viscosity to produce a homogenous blend. If the process set-up is limited in length, then a different type of static mixer is recommended.