Food Processing Unit Operations Multiple Choice Questions on “Resistance of the Filtering Cake”.
1. What is filter medium resistance?
a) Resistance by solids retained on filter
b) Resistance by liquid
c) Resistance due to pressure
d) Resistance due to concentration gradient
Answer: a
Clarification: Filter medium resistance is the resistance due to the solid particles which forms the cake and also the filter medium. It helps in measuring the average ability of solid.
2. What is the primary method of filtration?
a) Straining
b) Sedimentation
c) Centrifuge
d) Diffusion
Answer: a
Clarification: A particle is removed by straining when its size is larger than the size of the opening or the size of the pore in a filter bed. The primary method of filtration is straining.
3. What are the compressible cake forming materials?
a) Sand
b) Crystals
c) Salt
d) Cupric oxides
Answer: d
Clarification: A filter cake is formed by metal hydroxide particles substances that are retained on a filter are called compressible cake forming materials. Examples are Ferric hydroxide, cupric oxide and aluminum oxide.
4. What is present in filter medium in depth filtration?
a) Cellulose
b) Positive charge ions
c) Salt
d) Negative charge ions
Answer: a
Clarification: The filter medium consist of 0.5 to 3 m bed of coarse grains, layer of a few centimeters of fibers, cellulose sheets and a layer of granular filter aid.
5. What is the step involved in filter cake removal?
a) Washingand de-liquoring
b) Washing and adjusting temperature
c) Washing and adjusting pressure
d) De-liquoring and adjusting temperature
Answer: a
Clarification: Cake filtration is combined with washing and de-liquoring of the filter cake. The purpose of washing is to remove the mother liquor left behind in the cake after filtration when this liquid is regarded as contaminant or recovered as a valuable substance.
6. What is the demerit of de-liquoring by gas pressure?
a) Less efficacy
b) Less efficiency
c) Crack formation
d) Time consumption
Answer: c
Clarification: When the de-liquoring is done by gas pressure, cracks may appear which let pass the washing liquid. In any case, de-liquoring should be avoided before the washing.
7. What happens when de-liquoring is done by compression?
a) Cake becomes impermeable
b) Less efficiency
c) Crack formation
d) Time consumption
Answer: a
Clarification: If de-liquoring is done by compression the cake becomes impermeable. Therefore the squeezing pressure for intermediate de-liquoring should be lower than the pressure for washing.
8. What are the incompressible cake forming materials?
a) Sand
b) Ferric hydroxide
c) Salt
d) Cupric oxides
Answer: a
Clarification: Filter cakes which are composed of inorganic material with large size are incompressible materials. Some of the examples are sand and crystals.
9. What is added to increase the permeability of filtrate cake?
a) Filter aid
b) Salt
c) Sand
d) Ammonia
Answer: a
Clarification: Filter aids are inert powders which are added in the filtration unit to the liquid to be filtered and this increases the porosity and permeability of the cake.
10. Which of the following statements about expression of filter cake are correct?
Statement 1: It is used where de-liquoring by gas pressure is not possible.
Statement 2: It reduces the liquid content by mechanical means.
a) True, False
b) True, True
c) False, True
d) False, False