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GATE XL: Undergraduate Subjects in Engineering/Technology/Architecture

GATE XL · Work through your exam, one topic at a time.

All guide sections

Undergraduate Subjects in Engineering/Technology/Architecture

Domain scope

This domain covers the undergraduate engineering, technology, and architecture material that GATE XL draws on, chiefly through Food Technology (Section U) and the quantitative parts of life-science papers. The exam tests whether you can apply conservation laws, transport principles, unit operations, reaction kinetics, process control, and safety/environmental constraints to biological and food systems, not whether you can memorize equipment diagrams.

Core rules and concepts

  • Start every material-balance problem with a control volume and a basis, such as 1 h or 1000 kg feed. Write total mass and each component balance; do not assume volumes are additive unless densities are known.
  • Energy balances use enthalpy with a reference state; latent heat dominates in evaporation and drying. Heat-transfer rate is Q = U A ΔT_lm for a clean exchanger; fouling adds resistance.
  • Unit operations such as filtration, centrifugation, evaporation, drying, extraction, and sterilization are selected by driving force, phase behavior, and product quality. Thermal processes need D-value, z-value, and F0 reasoning, not just temperature.
  • Reaction and bioprocess kinetics depend on limiting substrate, biomass, and inhibition; continuous culture at steady state has dilution rate D = μ.
  • Process control uses sensor, transmitter, controller, and final element; PID tuning trades offset, oscillation, and stability. Safety includes CIP/SIP validation, allergen control, and effluent load.

Worked example

A juice evaporator concentrates 1000 kg/h of feed from 12% to 48% solids. Solids balance: 1000×0.12 = 0.48P, so P = 250 kg/h concentrate. Total balance: water removed = 1000 − 250 = 750 kg/h. Check water: feed water 880 kg/h; product water 130 kg/h; difference 750 kg/h. The answer is not 520 kg/h, which comes from subtracting solids percentages incorrectly.

Traps

Wet-basis versus dry-basis solids; forgetting solids in the removed stream; mixing mass and molar balances; using arithmetic mean ΔT instead of log mean; ignoring non-Newtonian viscosity; and treating D-value as a time independent of temperature.