Gas viscosity: estimation of molecular diameter

Principle

Expressed most simply, the viscosity of a fluid (liquid or gas) relates to its resistance to flow. The viscosity of a gas is determined in particular by the rate of transfer of the flow momentum from faster moving layers (laminas) to slower ones. The so-called transpiration methods provide a convenient way of measuring gas viscosities. In the approach used here, the flow rate of the gas (which is inversely proportional to its viscosity) is recorded by monitoring the evacuation of a vessel through a capillary tube under a constant pressure differential.

Tasks

1. Meassure the viscosities of the gases nitrogen, carbon dioxide, hydrogen and helium.
2. Use simple gas kinetic theory to estimate the molecular diamenter of each of the gases measured.

What you can learn about

• Kinetic theory of gases
• Mean free path
• Transport properties
• Laminar and turbulent flow
• Poiseuille's equation

Literature for this article als follows

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