Viscosity of dry atmospheric air:\nAt room temperature (around 20–25°C), the dynamic viscosity of air is approximately what value in centipoise (cP)?

Introduction / Context:
Dynamic viscosity is a measure of a fluid’s internal resistance to flow. For gases like air, viscosity values are much smaller than for liquids and are frequently needed in calculations for flow, heat transfer, and mass transfer around ambient conditions.

Given Data / Assumptions:

• Atmospheric air, dry, near 1 atm.
• Temperature ≈ 20–25°C (room temperature range).
• Viscosity unit conversion: 1 cP = 1 mPa·s.

Concept / Approach:
The dynamic viscosity of air at 20°C is about 1.8×10^-5 Pa·s, which equals 0.018 cP (since 1 Pa·s = 1000 cP). Rounded engineering estimates often use the 0.018–0.02 cP band. Many handbooks quote values between 0.017 and 0.020 cP depending on temperature and humidity. A value of 0.015 cP is a common approximate multiple-choice entry representing the same order of magnitude and is the only option in the correct range by powers of ten.

Step-by-Step Solution:

Verification / Alternative check:
Sutherland’s correlation for air viscosity near ambient yields values consistent with 0.017–0.020 cP; 0.015–0.02 cP is an acceptable MCQ bracket.

Why Other Options Are Wrong:

• 1.5, 15, 150 cP correspond to water-like or far higher viscosities, not gases.
• 0.5 cP is still ~25× too large for air at room temperature.

Common Pitfalls:
Confusing cP with cSt (kinematic viscosity) or mixing gas and liquid magnitudes by orders of magnitude.

Final Answer:
0.015 cP.