Food Processing Unit Operation Flashcards
7 cards from real Agricultural/Bioengineering practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Food Processing Unit Operation flashcards as text
In a counterflow heat exchanger used for milk pasteurization, which configuration provides the greatest thermal efficiency?
Answer: Counterflow with product and heating medium flowing in opposite directions
Counterflow configuration maintains a more uniform temperature driving force along the entire exchanger length, maximizing heat transfer efficiency.
The Reynolds number in a food processing pipeline is 1,800. What flow regime is present?
Answer: Laminar flow
A Reynolds number below 2,100 indicates laminar (streamline) flow in a pipe, where fluid layers move parallel without mixing.
Which drying method preserves heat-sensitive nutrients best while achieving very low final moisture content?
Answer: Freeze drying (lyophilization) under vacuum
Freeze drying removes water by sublimation at low temperatures, minimizing thermal degradation of vitamins, flavors, and bioactive compounds.
In centrifugal separation of cream from milk, increasing the bowl speed by a factor of 2 increases the centrifugal force by a factor of:
Answer: 4
Centrifugal force is proportional to the square of angular velocity (F = mω²r), so doubling speed quadruples the separating force.
What is the primary purpose of blanching vegetables before freezing?
Answer: To inactivate enzymes that cause quality deterioration during frozen storage
Blanching inactivates peroxidase, lipoxygenase, and other enzymes that cause off-flavors, color changes, and texture degradation during frozen storage.
In a rotary drum dryer processing grain, the 'critical moisture content' refers to:
Answer: The point where the drying rate transitions from constant to falling rate
Critical moisture content marks the transition from the constant-rate period (surface evaporation) to the falling-rate period (internal diffusion-controlled drying).
A plate-and-frame filter press is operating in constant-pressure filtration. As the filter cake builds up, the filtration rate:
Answer: Decreases as resistance through the cake grows
At constant pressure, increasing cake thickness adds resistance so that flow rate must decrease according to Darcy's law.