Temperature Effect – Dynamic Viscosity of Gases For most common gases, the dynamic viscosity increases as temperature rises due to enhanced molecular momentum transport.

Introduction:
This item contrasts the temperature–viscosity trends of gases versus liquids. Understanding the trend helps in heat-transfer and flow-friction predictions at elevated temperatures.

Given Data / Assumptions:

• Ideal or near-ideal gases over engineering temperature ranges.
• No phase change or chemical reaction.
• Pressure variations modest.

Concept / Approach:

Gas viscosity arises from molecular momentum exchange. As temperature increases, molecular speeds rise, increasing the rate and distance of momentum transport, hence dynamic viscosity mu increases (e.g., Sutherland’s formula for air).

Step-by-Step Solution:

Verification / Alternative check:

Empirical correlations (Sutherland) and tabulated data show monotonic increase of mu for air from ambient to high temperatures.

Why Other Options Are Wrong:

Unaffected or decreases contradict gas behavior (decrease applies to liquids). Other options introduce patterns not generally observed.

Common Pitfalls:

Applying liquid trends to gases; confusing dynamic viscosity with kinematic viscosity (which also depends on density).

Final Answer:

increases