# Food Processing Unit Operations Questions and Answers – Filtration at Constant Volumetric Flow

This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Filtration at Constant Volumetric Flow”.

1. How is flow rate calculated?
a) Driving force + total resistance
b) Driving force – total resistance
c) Driving force x total resistance
d) Driving force / total resistance

Explanation: Flow rate is defined as the volume of fluid which passes per unit time. The flow rate in the filtration can be calculated as the ratio of the driving force to total resistance offered by the filter cake.

2. How does the increase in filter cake affect the flow rate?
a) Increase then decrease
b) Increase
c) Decrease
d) Does not depend

Explanation: A filter cake is formed by the substances that are retained on a filter. The filter cake grows in the course of filtration. With increasing layer thickness, the flow resistance of the filter cake increases.

3. What law is applicable when the flow rate is laminar?
a) Poiseuille’s law
b) Newton’s law
c) Gauss’s law
d) Dalton’s law

Explanation: Filtration rate is directly proportional to the difference in pressure and inversely proportional to the fluid viscosity and to the hydraulic resistance of the cake and filter medium.

4. What is the relationship between temperature and filtrate volume?
a) Directly proportional
b) Indirectly proportional
c) Equal
d) Does not depend

Explanation: An increase in temperature increases the filtrate volume. This reduces the viscosity of the filtrate and therefore the filtrate volume also increases.

5. What is the demerit of increase in filtrate volume during filtration?
a) Solvent recovery
b) Time consumption
c) Efficiency
d) Power consumption

Explanation: Disadvantages of increased filtrate volume are solvent recovery and flammability issues. The use of surfactants such as sulphosuccinates can increase filtration rates and reduce equilibrium cake moisture during gas de-liquoring.
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6. What is constant rate filtration?
a) Q=dV/dt is kept constant
b) Q=dt/dV is kept constant
c) Q=dp/dt is kept constant
d) Q=dp/dV is kept constant

Explanation: The constant rate filtration Q=dV/dt is kept constant. The pressure drop is to be increased in order to overcome the increasing opposition due to cake build-up.

7. Which of the following is not the factor that controls the rate of filtration?
a) Particle Size of Solids.
b) Ratio of slimes to coarser particles.
c) Temperature
d) Feed solids concentration.

Explanation: Factors that control the rate of filtration are particle size of solids, ratio of slimes to coarser particles, filter aids, feed solids concentration, filter thickening, slurry pH and flocculation of fine solids

8. Does viscosity affect filtration?
a) True
b) False

Explanation: As concentration of the solids increases in the suspension, there is an increase in thickness of the filter cake. The filtration rate mainly depends on the viscosity of the slurry. Due to presence of solids in the suspension, a resistance force called viscosity is taken into consideration during the filtration.

9. What is the relationship between concentration and filtrate volume?
a) Directly proportional
b) Indirectly proportional
c) Equal
d) Does not depend

Explanation: Filtration rate is inversely proportional to concentration of the solution. When the solids are present in a very low concentration the filtration is high and rapid.

10. What is rate of filtration?
a) Pressure of filtrate per unit volume
b) Volume of filtrate collected per unit time
c) Pressure of filtrate per unit time
d) Volume of solution per unit time

Explanation: As the filter medium is penetrable only to the fluid, it retains the solid particles and permits only the fluid to pass through medium which is collected as the filtrate. The volume of filtrate collected per unit time is known as the rate of filtration.

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