Fluid movement through an actual packed bed can be modeled approximately as a ________________ model?
Show answer Hide answer
Answer: B. Dispersion
Explanation
Fluid flowing through a packed bed encounters solid obstacles causing velocity variations and backmixing phenomena. The dispersion model accounts for this axial mixing superimposed on overall unidirectional bulk fluid movement. This approach bridges the gap between ideal plug flow and completely backmixed continuous stirred tank reactors. Packed beds consist of solid catalyst particles packed tightly inside cylindrical tubular reactor shells. Axial dispersion quantifies the spreading of fluid elements along the longitudinal axis of the packed bed. Ideal plug flow assumes zero mixing along the flow direction, which rarely occurs in actual beds.
Option A ideal plug flow ignores fluid channelling and boundary layer friction caused by solid packing particles. Option C mixed flow assumes instantaneous and complete fluid blending throughout the entire reactor volume. Option D tanks in series is an alternative mathematical approximation but dispersion is standard for packed beds.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. Regarding the endothermic dissociation of CaCO3 inside a sealed container (CaCO3 ⇌ CaO + CO2), the partial pressure of CO2 rises if____________________?
Show answer Hide answer
Answer: B. The temperature is increased
Endothermic reactions absorb heat, meaning higher temperatures shift chemical equilibrium toward the product side. According to Van't Hoff equation, raising the temperature increases the equilibrium constant for endother...
Q2. Exposing a photographic plate to form a latent image serves as an illustration of a _______________ reaction?
Show answer Hide answer
Answer: D. Both B. and C.
Exposing photographic plates involves rapid photochemical reactions initiated by light exposure. Light photons provide the precise activation energy needed to reduce silver halide crystals into metallic silver. Both rapi...
Q3. Identify a reaction mechanism that aligns with the rate expression and reaction presented below?
Show answer Hide answer
Answer: D. A + A ⇌ AA; AA + B → A2B
Reaction mechanisms featuring pre-equilibrium steps followed by a rate-determining surface reaction yield corresponding rate laws. Rapid reversible adsorption steps establish pre-equilibrium concentrations before the slo...
Q4. For a _____________ order reaction, the reaction rate and the rate constant share identical units?
Show answer Hide answer
Answer: A. Zero
Zero-order reaction rates do not depend on reactant concentration, meaning rate equals the rate constant. Since concentration terms have a power of zero, the units of rate and rate constant remain identical. Reaction rat...
Q5. When the Thiele modulus is 10 in a first-order chemical reaction within a porous catalyst, the effectiveness factor is roughly equal to ____________________?
Show answer Hide answer
Answer: C. 0.1
At a high Thiele modulus of 10, pore diffusion heavily restricts the reaction, resulting in an effectiveness factor of approximately 0.1. Severe internal mass transfer limitations mean only the outer shell of the catalys...
Q6. The space time for a first-order reaction performed inside a plug flow reactor is__________________?
Show answer Hide answer
Answer: A. (1/k) ln C0/C
Integrating the plug flow reactor mole balance equation for a first-order reaction produces a logarithmic term. Space time equals the reciprocal of the rate constant multiplied by the natural logarithm of concentration r...