# Iron Making Questions and Answers – Ergun Equation for Packed Beds, Bed Fluidization and Elutriation

This set of Iron Making Multiple Choice Questions & Answers (MCQs) focuses on “Ergun Equation for Packed Beds, Bed Fluidization and Elutriation”.

1. The ∆P vs. v correlation is given by the ___________
a) Ergun equation
b) Euler equation
c) Eigen equation
d) Eureka equation

Explanation: The ∆P vs.v correlation for a packed bed of solid spheres of uniform size and density is well established and it is commonly known as the Ergun equation. A relation is derived between the friction factor and Reynolds number for lamellar flow and is further extended to turbulent flow, known as Ergun equation.

2. Solid particles in a packed bed start getting fluidized with the increasing in the ____________
a) Gas velocity
b) Liquid velocity
c) Vapour velocity
d) Hot metal velocity

Explanation: Solid particles in a packed bed start getting fluidized with the increasing in the gas velocity and is known as the onset of fluidization. Through further increase in the gas velocity the condition of elutriation can be achieved.

3. In Elutriation the individual particles start escaping the bed and combining the gas.
a) True
b) False

Explanation: In Elutriation the individual particles start escaping the bed and combining the gas. The minimum elutriation velocity (vt) is given by the famous Stokes equation. Strokes equation is used to obtain the critical value of velocity required for Elutriation to take place.

4. The bed permeability decrease in the case of particles with mixed sizes as the ___________
a) Void area decreases
b) Void area increases
c) Packed area decreases
d) Packed area increases

Explanation: The bed permeability decrease in the case of particles with mixed sizes as the void area also decreased. Low voidage means less space for the passage of gases through the bed which means less permeability of the bed.

5. The high gas velocity prevents the downward flow of liquid, known as ________
b) Flooding
c) Floating
d) Flowing

Explanation: The high gas velocity prevents the downward flow of liquid, known as loading. It is an extreme case as afterwards upward flow of liquid starts. It is an equilibrium state where pressure of the gas and the fluid is equal.

6. In which phenomena the liquid starts flowing upwards with the high increase in the gas velocity?
a) Flooding
b) Floating
c) Clogging
d) Clotting

Explanation: In flooding, the liquid starts flowing upwards with the high increase in the gas velocity. In this case the pressure applied by gas is very high which is used to flow the fluid mechanically upwards.

7. The granular zone of a blast furnace contains particles of non-uniform sizes and shapes.
a) True
b) False

Explanation: The granular zone of a blast furnace contains particles of non-uniform sizes and shapes. Also the densities of ore, coke and other materials are also different along with non-uniformity in sizes.

8. The void fraction is lower for ___________
a) Large spheres of uniform size
b) Small spheres of uniform size
c) Mixture of large and small spheres
d) Very large spheres of uniform size

Explanation: The mixture of large and small spheres is having the minimum void fraction as the packing efficiency is very high for this type of mixture. Smaller spheres fill the voids created between the larger spheres.

a) True
b) False

Explanation: When the gas pressure is equal to the fluid pressure, the condition is termed as loading. While when the gas pressure is higher than fluid pressure, fluid starts flowing upward. It is known as flooding.

Sanfoundry Global Education & Learning Series – Iron Making.

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