# Food Processing Unit Operations Questions and Answers – Filtration at Constant Pressure Drop

This set of Food Processing Unit Operations Questions and Answers for Campus interviews focuses on “Filtration at Constant Pressure Drop”.

1. What happens when the net driving force is positive?
a) Net fluid filtration takes place
b) Net fluid reabsorption takes place
c) Net fluid filtration stops
d) Net fluid filtration stops

Explanation: The net driving force for fluid movement is the net pressure gradient is known by the sum of the individual hydrostatic and oncotic pressures. When the net driving force is positive, there is net fluid filtration takes place.

2. What happens when the net driving force is negative?
a) Net fluid filtration takes place
b) Net fluid reabsorption takes place
c) Net fluid filtration stops
d) Net fluid filtration stops

Explanation: The net driving force is the net pressure gradient for a fluid movement. It is calculated as the sum of the individual oncotic and hydrostatic pressures. When net driving force is negative, there is net fluid reabsorption.

3. Are these statements about the pressure drop in filtration true?
Statement 1: Due to the increase in the solids deposit in the pores.
Statement 2: For constant solids concentration at the inlet increase in this pressure drop with time is constant.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: The filter media exhibit a resistance to flow, which is increased by the solids deposit in the pores. For constant solids concentration at the inlet and constant retention the increase in this pressure drop with time is constant.

4. How does pressure drop at initial stage of filtration?
a) Pressure drop is small
b) Pressure drop is large
c) Does not depend on pressure drop
d) At equilibrium throughout the process

Explanation: In the early stages of the filtration cycle, the pressure drop across the filter medium is small and filtration proceeds at constant rate. As the cake increases, the process becomes more and more a constant pressure one.

5. When does the pressure difference increase in filtration?
a) If the constant rate is maintained
b) If the cake thickness decreases
c) If the cake thickness increases
d) There is no pressure difference throughout the process

Explanation: As the thickness of the cake increases the resistance to flow of filtrate increases and rate of filtration gradually decreases. If rate is maintained to be constant then pressure difference driving force will increase.
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6. Is filter press used to decrease pump pressure?
a) True
b) False

Explanation: A filter press uses increased pump pressure to maximize the filtration rate.Filter presses work in a batch manner. It is used in liquid/solid separation. It separates the solids and liquids using pressure filtration.

7. What is capillary pressure curve?
a) A plot of saturation of the cake versus pressure difference
b) A plot of saturation of the cake versus temperature difference
c) A plot of concentration of the filtrate versus temperature difference
d) A plot of concentration of the filtrate versus pressure difference

Explanation: A plot of saturation of the cake versus pressure difference in an equilibrium state is called capillary pressure curve. It is used in reservoir engineering primarily for calculating initial fluid contacts and transition zones.

8. What law is applicable when liquid velocity through the pores is low and pore size is small?
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.

9. What is the main driving force for the filtrate flow?
a) Difference between the atmospheric pressure and the pressure in the equipment
b) Atmospheric pressure only
c) Partial pressure only
d) Difference between the atmospheric pressure and the partial pressure

Explanation: The main driving force for the filtrate flow is difference between the atmospheric pressure and the pressure in the equipment. Though the hydrostatic pressure still contributes to the driving force, it is usually smaller than the vacuum pressure produced by the pump.

10. Are these statements about the Discontinuous pressure filters true?
Statement 1: Application of large pressure difference.
Statement 2: Economical and rapid filtration.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: Discontinuous pressure filters generally applies large pressure difference where it is economical and also have rapid filtration. Examples are plate and frame filter press and shell and leaf press.

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