CFTRI M.Sc. (Food Technology) Food Engineering Syllabus

What is the function of baffles in a mixing tank?

Baffles prevent swirling and vortex formation, convert rotational flow into top-to-bottom turbulence, and improve mixing efficiency.

What is the Power number (Np) in mixing?

A dimensionless number relating impeller power to fluid properties: Np = P/(ρN³D⁵), where N=impeller speed and D=impeller diameter.

How is the impeller Reynolds number defined for mixing?

Re = ρND²/μ, where N is rotational speed (rev/s) and D is impeller diameter.

What is the difference between mixing of low-viscosity liquids and high-viscosity/pastes?

Low-viscosity liquids use high-speed turbines/propellers relying on turbulence; high-viscosity pastes use low-speed, large close-clearance mixers (ribbon, planetary, kneaders) relying on shear and folding.

Name common equipment for mixing dry powders/solids.

Ribbon blender, tumbling (V-cone, double-cone) mixers, fluidized-bed mixers, and screw/sigma-blade mixers.

What is the difference between dispersion and emulsification?

Dispersion distributes solid particles in a fluid; emulsification creates a stable mixture of two immiscible liquids (e.g., oil in water) using shear and emulsifiers.

Define a unit operation in food engineering.

A basic physical step in processing (e.g., mixing, filtration, evaporation, drying) that is common across many processes and governed by the same engineering principles.

What is the working principle of a centrifugal pump?

A rotating impeller imparts kinetic energy to the liquid, which is converted to pressure head in the casing/diffuser; used for low-viscosity liquids at moderate-high flow.

When are positive displacement pumps preferred over centrifugal pumps?

For high-viscosity fluids, precise/metered dosing, high pressures, or shear-sensitive products; they deliver a fixed volume per cycle (e.g., gear, lobe, peristaltic pumps).

What is the principle of a plate heat exchanger?

Thin corrugated plates create alternating channels for hot and cold fluids, giving a large surface area and turbulence for efficient heat transfer; widely used in pasteurization.

What is the function of a heat exchanger in food processing?

To transfer thermal energy between fluids for heating, cooling, pasteurization, or sterilization without mixing the streams (in indirect types).

Define separation processes in food engineering.

Operations that divide a mixture into two or more fractions of different composition based on differences in physical/chemical properties (size, density, solubility, volatility).

What is filtration?

Separation of solids from a fluid by passing the suspension through a porous medium that retains solids (cake/filtrate) while allowing the fluid to pass.

State the basic relationship governing filtration rate.

Filtration rate is proportional to pressure drop and inversely proportional to medium plus cake resistance and fluid viscosity (dV/dt ∝ ΔP·A / [μ(Rcake+Rmedium)]).

What is the difference between dead-end and cross-flow filtration?

Dead-end: feed flows perpendicular to the filter, cake builds up. Cross-flow: feed flows parallel/tangential to the membrane, sweeping away solids to reduce fouling (used in membrane filtration).

Rank microfiltration, ultrafiltration, nanofiltration, and reverse osmosis by pore size/retained species.

Microfiltration (largest, ~0.1–10 µm, bacteria/fat globules) > Ultrafiltration (proteins/macromolecules) > Nanofiltration (divalent ions, small molecules) > Reverse osmosis (smallest, only water passes, retains ions/sugars).

What drives reverse osmosis?

Applied pressure greater than the osmotic pressure forces water through a semipermeable membrane against the concentration gradient, retaining dissolved solutes.

What is the principle of centrifugal separation?

Centrifugal force (much greater than gravity) accelerates the settling of denser components, separating phases by density difference (e.g., cream separation, clarification).

Differentiate a centrifugal separator (clarifier) from a centrifugal decanter.

A clarifier/separator removes fine solids or separates immiscible liquids (e.g., cream from milk); a decanter (scroll) handles higher solids and continuously discharges the solid phase via a screw conveyor.

State Stokes' law for settling velocity.

v = d²(ρp − ρf)g / 18μ, the terminal settling velocity of a small spherical particle in laminar (creeping) flow.

What is sedimentation?

Gravity-driven separation of suspended solid particles from a liquid by allowing them to settle, forming a clarified supernatant and a sediment.

What is the difference between distillation and evaporation as separation methods?

Distillation separates components by differences in volatility and recovers the vapor (e.g., alcohol). Evaporation concentrates a solution by boiling off and discarding the volatile solvent (usually water).

What is extraction (leaching/solvent extraction)?

Separation of a soluble component from a solid or liquid by dissolving it into a selective solvent (e.g., oil extraction from seeds with hexane).

What is the principle of sieving/screening in solids separation?

Particles are separated by size using a screen; particles smaller than the aperture pass (undersize), larger ones are retained (oversize).

Define mechanical operations (size reduction) in food processing.

Physical operations that change the size or form of solids—such as crushing, grinding, cutting, and milling—to increase surface area, aid mixing, or meet product specifications.

State Rittinger's law of size reduction.

Energy required is proportional to the new surface area created: E = KR(1/d₂ − 1/d₁); best suited for fine grinding.

State Kick's law of size reduction.

Energy needed is proportional to the size reduction ratio: E = KK·ln(d₁/d₂); applies best to coarse crushing.

State Bond's law of size reduction.

Energy is proportional to the new crack length: E = KB(1/√d₂ − 1/√d₁); used for intermediate grinding (work index).

Name common size-reduction equipment and the materials they suit.

Hammer mill (brittle/fibrous solids), ball mill (fine grinding of hard solids), roller mill (grains/flour), disc/attrition mill (wet/fibrous), and cutters/slicers (fruits, vegetables, meat).

What is the principle of a ball mill?

A rotating cylinder partly filled with grinding balls; impact and attrition from cascading balls reduce particle size—effective for fine grinding of hard, brittle materials.

What is the critical speed of a ball mill?

The rotational speed at which centrifugal force pins the balls to the wall so they no longer cascade (no grinding); mills operate at 65–80% of critical speed.