Question

Incompressible flow is that type of flow in which ____________ is constant for the fluid flow.

• A. Surface tension
• B. Density
• C. Temperature
• D. Thermal conductivity

Hint:

Liquid = Incompressible (Density stays same). Gas = Compressible (Density changes).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Fluids are generally classified as compressible or incompressible based on how easily their volume (and thus density) changes under pressure.

Step 2: Detailed Explanation:
A flow is defined as Incompressible if the Density ($\rho$) of the fluid remains constant throughout the flow process.
Mathematically, for an incompressible flow:
\[ \frac{d\rho}{dt} = 0 \]
Most liquids (including milk and water) are treated as incompressible because their volume changes only negligibly even under significant pressure.
Gases, however, are compressible; their density changes significantly with pressure and temperature changes.
The other options provided are:
- Surface tension (Option 1): Relates to surface properties, not volume/pressure relations.
- Temperature (Option 3): If temperature is constant, it's called "Isothermal" flow.
- Thermal conductivity (Option 4): Relates to heat transfer efficiency, not fluid compression.
In dairy engineering calculations (like using Bernoulli's equation), we almost always assume milk flow is incompressible to simplify the math.

Step 3: Final Answer:
In incompressible flow, Density is constant.