National Technical Qualification — Food Engineer (식품기사) and Food Industrial Engineer (식품산업기사) · South Korea · Human Resources Development Service of Korea (HRDK), Q-Net
Original practice questions written to the published syllabus · not past papersMass and energy balances and the three transfer processes — momentum, heat and mass — applied to foods: pumping viscous products, heating cans and pouches, and moisture and gas movement through foods and packaging films.
In the exams: GATE XE-G Section 4 (mass and energy balance, momentum transfer, heat transfer, mass transfer); ICAR AIEEA-PG Code 18 Unit II
How our questions for National Technical Qualification spread across the units of Transport Phenomena in Food Processing: Fluid Flow, Heat & Mass Transfer. Difficulty: 1 easy, 7 medium, 7 hard.
| Energy balances and steam tables | 3 | |
| Heat exchangers: plate, tubular and scraped-surface; LMTD and effectiveness | 3 | |
| Material balances on mixing, concentration and drying | 2 | |
| Units, dimensions and dimensional analysis | 1 | |
| Flow in pipes: Reynolds number, friction factor and pressure drop for Newtonian fluids | 1 | |
| Flow of non-Newtonian foods in pipes | 1 | |
| Pumps for foods: centrifugal and positive-displacement | 1 | |
| Steady-state conduction through slabs, cylinders and composite walls | 1 | |
| Convection: film coefficients and dimensionless numbers | 1 | |
| Convective mass transfer | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
When scaling a mixing process from a 50 L pilot vessel to a 5,000 L production vessel, engineers commonly keep which quantity constant when the aim is similar turbulence intensity?
B. Power input per unit volume
Constant P/V is a common scale-up rule for turbulent mixing; constant rpm would give far higher power per volume in the large tank, and constant total power far lower.
Further reading: Earle, Unit Operations in Food Processing
100 kg of carrots at 88 % moisture (wet basis) are dried to 8 % moisture (wet basis). The water removed is closest to
A. 87.0 kg
Solids = 12 kg; dried product = 12/0.92 = 13.04 kg; water removed = 87.0 kg. 80.0 kg subtracts percentages; 88.0 kg removes all water; 81.0 kg takes 92 % of 88 kg.
Further reading: Singh and Heldman, Introduction to Food Engineering
2,000 kg/h of milk (cp = 3.9 kJ/kg K) is heated from 10 °C to 72 °C by steam condensing at 120 °C (hfg = 2,202 kJ/kg), condensate leaving saturated. The steam needed is closest to
A. 220 kg/h
ṁs = 2,000 × 3.9 × 62/2,202 = 220 kg/h. 214 uses hfg at 100 °C; 255 heats from 0 °C; 56 omits cp.
Further reading: Singh and Heldman, Introduction to Food Engineering
A cold-store wall has 100 mm of polyurethane (k = 0.025 W/m K) with surface coefficients 10 W/m² K (inside) and 25 W/m² K (outside). Inside −25 °C, outside 30 °C. The heat gain per m² is closest to
C. 13.3 W
R = 1/25 + 0.1/0.025 + 1/10 = 4.14 m² K/W; q = 55/4.14 = 13.3 W. 13.8 W ignores the films; 102 W uses 10 mm of insulation instead of 100 mm; 393 W omits the insulation.
Further reading: Singh and Heldman, Introduction to Food Engineering
A cooling section of a juice line underperforms. The juice-side film coefficient is about 800 W/m² K and the water side about 5,000 W/m² K. The most effective way to raise the overall coefficient is to
A. increase juice-side turbulence
The smaller film coefficient controls U; improving the juice side helps most. Raising water temperature reduces the driving force.
Further reading: Incropera and DeWitt, Fundamentals of Heat and Mass Transfer
Carcass weight loss during chilling can be reduced by
B. lowering air velocity and raising humidity once the surface is cool
Evaporation rate rises with km (air velocity) and the vapour-concentration difference; spray chilling and humid air reduce it.
Further reading: Earle, Unit Operations in Food Processing
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