Computational fluid dynamics in formulation MCQs With Answer

Introduction: Computational Fluid Dynamics (CFD) in formulation bridges fluid mechanics and pharmaceutical formulation design by using numerical simulations to predict fluid flow, heat and mass transfer, and particle behaviour in manufacturing processes. This blog presents targeted MCQs to help M.Pharm students strengthen core CFD concepts relevant to drug formulation — including governing equations, discretization methods, turbulence and multiphase models, mesh generation, solver selection, and practical applications such as mixing, spray drying, inhalation aerosols, and scale-up. The questions emphasize interpretation of results, model validation, and rheology of formulation media, equipping students to apply CFD for optimization, troubleshooting, and regulatory‑grade documentation in formulation development.

Q1. What is the fundamental set of equations solved in CFD for incompressible fluid flow?

• Maxwell’s equations
• Navier–Stokes equations coupled with continuity equation
• Schrödinger equation
• Arrhenius equation

Correct Answer: Navier–Stokes equations coupled with continuity equation

Q2. Which nondimensional number is most commonly used to predict whether flow in a pipe or mixer is laminar or turbulent?

• Biot number
• Reynolds number
• Péclet number
• Damköhler number

Correct Answer: Reynolds number

Q3. In CFD practice for pharmaceutical mixing, what does a high Péclet number indicate?

• Dominant chemical reaction over diffusion
• Dominant molecular diffusion over convective transport
• Dominant convective transport over molecular diffusion
• Flow is compressible

Correct Answer: Dominant convective transport over molecular diffusion

Q4. Which discretization method is most commonly used in commercial CFD codes for conservation laws in formulation processes?

• Finite Volume Method (FVM)
• Finite Difference Method (FDM)
• Boundary Element Method (BEM)
• Spectral Method

Correct Answer: Finite Volume Method (FVM)

Q5. For simulating turbulent flow in an industrial spray dryer for powders, which turbulence model is a good balance between accuracy and computational cost?

• Direct Numerical Simulation (DNS)
• Large Eddy Simulation (LES)
• Reynolds-Averaged Navier–Stokes with k-ε model
• Potential flow model

Correct Answer: Reynolds-Averaged Navier–Stokes with k-ε model

Q6. Which boundary condition is appropriate to model an impermeable wall where no slip is assumed?

• Periodic boundary
• Inlet velocity boundary
• No-slip wall boundary
• Pressure outlet boundary

Correct Answer: No-slip wall boundary

Q7. When modelling multiphase flows with a free surface (e.g., liquid film coating), which method tracks the interface between liquid and gas?

• Volume of Fluid (VOF) method
• Lattice Boltzmann method
• k-ω turbulence model
• Implicit Euler method

Correct Answer: Volume of Fluid (VOF) method

Q8. In particle-laden flows such as spray atomization, which approach treats the continuous fluid and discrete particles separately?

• Single-phase Eulerian method
• Homogeneous mixture model
• Eulerian–Lagrangian (discrete particle) approach
• Pure Lagrangian for fluid

Correct Answer: Eulerian–Lagrangian (discrete particle) approach

Q9. Which mesh property is most critical for resolving thin boundary layers near a coated tablet surface?

• Large, coarse cells near the wall
• High aspect ratio cells normal to the wall (fine layering)
• Uniform cubic cells everywhere
• No need for mesh refinement near walls

Correct Answer: High aspect ratio cells normal to the wall (fine layering)

Q10. What is the Courant–Friedrichs–Lewy (CFL) condition important for in transient CFD simulations?

• Ensuring chemical equilibrium
• Setting time step limit for numerical stability in explicit schemes
• Choosing boundary conditions
• Selecting turbulence models

Correct Answer: Setting time step limit for numerical stability in explicit schemes

Q11. Which rheological model is commonly used to represent shear-thinning behavior of polymeric or biologic formulations?

• Newtonian model
• Bingham plastic model only
• Power-law (Ostwald–de Waele) model
• Ideal gas model

Correct Answer: Power-law (Ostwald–de Waele) model

Q12. When validating a CFD model of a mixing vessel used for suspension formulations, which experimental measurement is most useful for direct comparison?

• Color of the mixture
• Residence time distribution and concentration profile over time
• Ambient laboratory temperature only
• Manufacturer’s mixer brand

Correct Answer: Residence time distribution and concentration profile over time

Q13. In modelling aerosol deposition in the respiratory tract, which physical phenomenon must be accounted for to predict particle fate accurately?

• Electrochemical reactions only
• Brownian diffusion, inertial impaction, and sedimentation
• Pure thermal conduction only
• Perfect mixing assumption

Correct Answer: Brownian diffusion, inertial impaction, and sedimentation

Q14. What is the main advantage of using Large Eddy Simulation (LES) over RANS for certain pharmaceutical mixing problems?

• LES is cheaper and always less accurate
• LES resolves large turbulent structures and provides more detailed transient flow information
• LES ignores turbulence entirely
• LES eliminates the need for boundary conditions

Correct Answer: LES resolves large turbulent structures and provides more detailed transient flow information

Q15. Which post-processing quantity is most informative for assessing mixing quality in a stirred tank for liquid formulation?

• Static pressure at one point
• Variance or coefficient of variation of tracer concentration field
• Only the maximum velocity magnitude
• Mesh cell count

Correct Answer: Variance or coefficient of variation of tracer concentration field

Q16. For numerical solution convergence monitoring, which criterion indicates that an iterative CFD solver has reached a steady solution?

• Residuals decrease and plateau at or below set tolerance
• Mesh size increases during iterations
• Physical time is negative
• Boundary conditions change each iteration

Correct Answer: Residuals decrease and plateau at or below set tolerance

Q17. In scale-up of a mixing process, which CFD-derived parameter is frequently scaled to preserve mixing performance?

• Color of stirrer
• Power number or power per unit volume (P/V)
• Number of operators
• Ambient humidity

Correct Answer: Power number or power per unit volume (P/V)

Q18. When coupling CFD with a population balance model (PBM) for particulate processes like crystallization, what does the PBM provide?

• Single-valued pressure field
• Particle size distribution evolution due to nucleation, growth, aggregation and breakage
• Only temperature distribution
• Mesh refinement strategy

Correct Answer: Particle size distribution evolution due to nucleation, growth, aggregation and breakage

Q19. Which numerical artifact can appear when the mesh is too coarse relative to flow gradients, causing unphysical oscillations in scalar fields?

• Gibbs phenomenon or numerical dispersion/oscillations
• True experimental noise
• Perfect agreement with experiments
• Automatic mesh refinement

Correct Answer: Gibbs phenomenon or numerical dispersion/oscillations

Q20. For modelling heat and mass transfer during spray drying of pharmaceuticals, which coupling is essential within the CFD model?

• Only hydrodynamics with no heat or mass transfer
• Coupling of airflow (fluid dynamics), droplet evaporation (mass transfer) and heat transfer with particle temperature change
• Only structural mechanics
• Purely steady-state incompressible assumption with no evaporation

Correct Answer: Coupling of airflow (fluid dynamics), droplet evaporation (mass transfer) and heat transfer with particle temperature change

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