1. The dispersion model accounts for ____
a) Deviation from ideal PFR
b) Modelling ideal CSTR
c) Combining batch and CSTR
d) CSTRs connected in parallel
Explanation: Dispersion model involves a modification of the ideal PFR. It imposes axial dispersion on plug flow
2. The the species continuity equation for the axial dispersion model is ____
a) u\(\frac{∂C_A}{∂z} = \frac{∂D_a}{∂z}\frac{∂C_A}{∂z}\) + (rA)C
b) u\(\frac{∂C_A}{∂z} = \frac{∂D_a}{∂z}\frac{∂C_A}{∂z}\) + C
c) \(\frac{∂C_A}{∂z} = \frac{∂D_a}{∂z}\frac{∂C_A}{∂z}\) + (rA)C
d) u\(\frac{∂C_A}{∂z} = \frac{∂D_a}{∂z}\frac{∂C_A}{∂z}\) + (rA)
Explanation: For statistically stationary flow, the species continuity equation for the axial dispersion model is u \(\frac{∂C_A}{∂z} = \frac{∂D_a}{∂z}\frac{∂C_A}{∂z}\) + (rA)C
u is taken to be the mean (plug flow) velocity through the vessel, and Da is an axial dispersion coefficient to be obtained by means of experiments.
3. If Da is diffusivity, CT is tracer concentration and UT is overall heat transfer coefficient, then the pulse tracer balance with dispersion is obtained as ____
a) \(\frac{∂^2 C_T}{∂z^2} – \frac{∂U_T}{∂z} = \frac{∂C_T}{∂z} \)
b) Da\(\frac{∂^2 C_T}{∂z^2} – \frac{∂U_T}{∂z} =\frac{∂C_T}{∂z} \)
c) Da\(\frac{∂^2 C_T}{∂z^2} + \frac{∂U_T}{∂z} =\frac{∂C_T}{∂z} \)
d) Da\(\frac{∂C_T}{∂z^2} – \frac{∂U_T}{∂z} =\frac{∂C_T}{∂z} \)
Explanation: The equation \(\frac{∂^2 C_T}{∂z^2} – \frac{∂U_T}{∂z} = \frac{∂C_T}{∂z} \) is obtained by a combination of mole balance on inert tracer and the molar flow rate of tracer by both convection and dispersion.
4. The range of reactor peclet number for open tubes is ____
a) 106
b) 1010
c) 102
d) 103
Explanation: Peclet number for open tubes is greater than that in packed beds. In open tubes, there is no restriction to flow velocity.
5. The dispersion model is a ____
a) Two parameter model
b) One parameter model
c) No parameter model
d) Three parameter model
Explanation: Dispersion model is a one parameter model. The parameter modelling the non – ideal condition is the dispersion coefficient.
6. State true or false.
The fluidized bed reactor is used for mixed flow of solids.
a) true
b) false
Explanation: Fluidised bed provides high agitation of solids by high fluid velocity. The gas flow is more complicated than mixed flow.
7. Which of the following does not provide plug flow of Solid – fluids?
a) Fluidised bed reactor
b) Countercurrent flow in blast furnaces
c) Crossflow in moving belt
d) Concurrent flow in driers
Explanation: Blast furnaces and cement kilns provide plug flow in countercurrent operation. Moving belt feeders are used in furnaces. Cocurrent flow is employed in polymer driers.
8. Which of the following does not control the design of fluid – solid reactor?
a) Reaction kinetics for single particles
b) Density of fluid being treated
c) Size distribution of solids
d) Flow patterns of solids and fluid
Explanation: The complexity of the reaction determines the use of flow reactor or plug flow reactor. The variation of temperature conditions determines the flow patterns of fluid by affecting the viscosity. The range of sizes determines the operational factors.
9. If \(\frac{τ}{t}\) = 0.5, average conversion for a particle B of constant size in a mixed flow reactor for film resistance controlling is ____
a) 0.45
b) 0.38
c) 0.536
d) 0.743
Explanation: 1-\(\overline{X_{(B)}}\) = 0.5(\(\frac{τ}{\overline{t}}) – \frac{1}{3!}(\frac{τ}{\overline{t}})^2+\frac{1}{4!} (\frac{τ}{\overline{t}})\)3-…, as obtained by expansion.
1-\(\overline{X_{(B)}}\) = 0.4635 and \(\overline{X_{(B)}}\) = 0.536
10. If \(\frac{τ}{t}=\frac{1}{3},\) average conversion for a particle B of constant size in a mixed flow reactor for chemical reaction controlling is ____
a) 0.92
b) 0.98
c) 0.75
d) 0.76
Explanation: \(\overline{X_{(B)}} = 3(\frac{\overline{t}}{τ}) -6 (\frac{\overline{t}}{τ})^2+ 6(\frac{\overline{t}}{τ})^3(1-e^\frac{τ}{\overline{t}}, 1-\overline{X_{(B)}}\) = 0.078 and \(\overline{X_{(B)}}\) = 0.92