GATE — Life Sciences (XL) with Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersFluid properties, pumping, thermodynamics and heat transfer worked as dairy plant problems.
In the exams: ICAR AICE subject 38 Units 1 and 4; ICAR AIEEA-PG group 17 Unit III (fluid mechanics, pumps, heat transfer, thermodynamics, dimensional analysis); GATE XL-U Section 4; GATE AG dairy and food engineering
How our questions for GATE spread across the units of Fluid Flow, Thermodynamics & Heat Transfer in Dairy Plants. Difficulty: 6 easy, 43 medium, 0 hard.
| Sanitary centrifugal and positive displacement pumps; pump selection | 6 | |
| Diffusion and mass transfer coefficients | 6 | |
| Dimensionless numbers and dimensional analysis | 6 | |
| Fluid properties and Bernoulli's equation | 5 | |
| Pipe flow, Reynolds number and friction losses | 5 | |
| Flow of non-Newtonian dairy fluids | 4 | |
| Laws of thermodynamics; steam tables | 4 | |
| Conduction, convection and radiation | 4 | |
| Fins and insulation | 4 | |
| Heat exchangers: LMTD and effectiveness-NTU | 3 | |
| Mass and energy balances in dairy processes | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In Bernoulli's equation written in head form, the term v²/2g represents:
A. Velocity head
p/ρg is pressure head, z elevation head, v²/2g velocity head; friction losses are added for real flow.
Further reading: Singh and Heldman, Introduction to Food Engineering
In a regenerative plate pasteuriser, pasteurised milk is kept at a higher pressure than raw milk so that:
A. Any leak runs from pasteurised to raw
A pinhole must not let raw milk contaminate pasteurised milk; pressure differential is a public-health control.
Further reading: Tetra Pak Dairy Processing Handbook
Pipe flow is generally laminar when the Reynolds number is below about:
B. 2,100
Below about 2,100–2,300 laminar; above about 4,000 turbulent.
Further reading: Singh and Heldman, Introduction to Food Engineering
Doubling the velocity of a fully turbulent flow in a smooth pipe raises the friction head loss by a factor of about:
A. 3.4
h_f ∝ f v² with f ∝ Re^(−0.25), so h_f ∝ v^1.75; 2^1.75 ≈ 3.4.
Further reading: Singh and Heldman, Introduction to Food Engineering
Stirred yoghurt loses viscosity when pumped and recovers only partly at rest. This is:
D. Thixotropy
Shearing breaks the protein network; only part rebuilds with time.
Further reading: Steffe, Rheological Methods in Food Process Engineering
Air left in a steam sterilising chamber is harmful mainly because:
C. It lowers the temperature at that pressure
The temperature depends on steam partial pressure; air pockets give cold spots.
Further reading: Steam tables
Which mode of heat transfer needs no material medium?
B. Radiation
Radiation travels as electromagnetic waves; conduction and convection need matter.
Further reading: Incropera et al., Fundamentals of Heat and Mass Transfer
Halving the thickness of a cheese reduces the time for salt to equalise by diffusion to about:
D. One quarter
Diffusion time scales with distance squared.
Further reading: Geankoplis, Transport Processes and Separation Process Principles
Which dimensionless number is used to characterise natural convection?
B. Grashof
Gr = gβΔTL³/ν² measures buoyancy against viscosity.
Further reading: Incropera et al., Fundamentals of Heat and Mass Transfer
Multiple-effect evaporators save energy mainly because:
B. Vapour from one effect heats the next
Reusing latent heat in successive effects raises steam economy roughly in proportion to the number of effects.
Further reading: Singh and Heldman, Introduction to Food Engineering
Ten here, 49 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
An AI operating system for agriculture: free guides, manuals and tools written for every country.