Question

For liquid foods, viscosity is inversely related to their ________. 
 

• A. Heat transfer efficiency
• B. Total soluble solids
• C. Concentration
• D. Stability

Hint:

Thicker, more viscous liquids do not circulate well during heating, which slows down heat transfer. This makes viscosity inversely proportional to heat transfer efficiency.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Viscosity is a measure of a fluid's resistance to flow and gradual deformation by shear or tensile stress.
In food engineering, physical properties such as viscosity directly influence processing parameters, including pumping, mixing, and thermal exchange.
Detailed Explanation:
The viscosity of liquid foods has an inverse relationship with their heat transfer efficiency, especially during convective heat transfer:
- High-viscosity fluids (such as purées, concentrates, or starch pastes) resist laminar and turbulent flow.
- This resistance reduces fluid circulation and limits convective currents near heat-exchange surfaces, which decreases the convective heat transfer coefficient ($h$).
- As a result, heat is transferred primarily via slower conduction rather than convection, lowering the overall heat transfer efficiency.
- Conversely, low-viscosity liquids (such as fruit juices or milk) flow easily, promoting mixing and turbulent flow, which increases heat transfer efficiency.
- Total soluble solids (B) and Concentration (C) generally have a direct relationship with viscosity (as solids or concentration increase, viscosity increases).

Step 2: Final Answer:
For liquid foods, viscosity is inversely related to their heat transfer efficiency.