During normal laminar airflow, resistance is dependent upon which characteristic of the gas?

During normal laminar airflow, resistance is dependent upon which characteristic of the gas?

• A. Density
• B. Viscosity
• C. Molecular weight
• D. Vapor pressure

Answer: (B)

In laminar flow, the resistance to moving the gas through a tube is governed by viscous (shear) forces. The pressure drop needed to drive a given flow is proportional to the dynamic viscosity of the gas, described by the relation ΔP ∝ μ for a cylindrical tube of fixed length and radius and a set flow rate. This means a gas with higher viscosity experiences more resistance and requires more pressure to achieve the same flow. Density can influence whether flow is laminar or turbulent (via the Reynolds number), but once laminar, density doesn’t set the resistance as directly as viscosity does. Molecular weight and vapor pressure don’t determine laminar flow resistance in this context. Therefore, viscosity is the key characteristic.

In laminar flow, the resistance to moving the gas through a tube is governed by viscous (shear) forces. The pressure drop needed to drive a given flow is proportional to the dynamic viscosity of the gas, described by the relation ΔP ∝ μ for a cylindrical tube of fixed length and radius and a set flow rate. This means a gas with higher viscosity experiences more resistance and requires more pressure to achieve the same flow. Density can influence whether flow is laminar or turbulent (via the Reynolds number), but once laminar, density doesn’t set the resistance as directly as viscosity does. Molecular weight and vapor pressure don’t determine laminar flow resistance in this context. Therefore, viscosity is the key characteristic.