In a two-phase system where the continuous phase remains in place, the gas hold

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Question
In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where V_s and V_t are the superficial gas velocity and bubble rise velocity)
Options
A. H = V_s/(V_s-V_t)
B. H = V_s/(V_s+ V_t)
C. H = V_s/(V_s.V_t)
D. H = (V_s+V_t)/V_s

Correct Answer

H = V_s/(V_s+ V_t)

2. The advantage of axial flow impellers over radial flow impellers is that axial flow impellers
Options
A. provide better lift of solids
B. provide high shear conditions
C. provide low shear conditions
D. are cheaper to build

5. If the stirrer speed is too slow, bubbles will accumulate and coalescese under the impeller. This phenomenon is known as a
Options
A. coalesced impeller
B. flooded impeller
C. river impeller
D. dry impeller

6. For turbulent flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Re_i, is Reynolds number for agitator; D_i, stirrer diameter and N, stirrer speed)
Options
A. N_p = K(Re_i)^-1
B. N_p = N²Di(Re_i)^-1
C. N_p = K
D. Can't be correlated

7. Which of the following will have the largest interfacial area per unit volume?
Options
A. A bubble with a diameter of 1 mm
B. A bubble with a diameter of 5 mm
C. A bubble with a diameter of 15 mm
D. A bubble with a diameter of 50 mm

8. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
Options
A. a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
B. as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
C. as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
D. A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate

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