Transport of Heat, Mass and Momentum - APHY 140 LECT 5

Gas Properties and Viscosity

• Kinematic viscosity (ν) is dependent on the dynamic viscosity (μ) and density (ρ) of a gas, expressed as ν = μ/ρ.
• The coefficient of dynamic viscosity (μ) defines the internal resistance of a fluid to flow and is a measure of momentum transfer relative to the velocity gradient in the fluid.

Momentum Transfer

• The direction of the flux of momentum relative to a surface is determined by the momentum gradient which indicates the flow direction.

Thermal Properties

• Thermal diffusivity (κ) is related to the thermal conductivity of air, heat capacity, and density, signifying how rapidly heat spreads through the material.
• The rate of heat transfer in heat transfer processes depends on the temperature gradient, area of transfer, and thermal conductivity of the material.

Molecular Motion

• The average distance a molecule travels between collisions is known as the mean free path.
• Viscosity in moving air arises from intermolecular friction and the interactions among air particles during movement.

Air Flow Dynamics

• Increased velocity of air flow over a solid surface is caused by a decrease in surface roughness or obstacles that disrupt airflow, leading to laminar flow conditions.

Kinetic Theory and Transfer Processes

• The kinetic theory of gases is significant in determining properties like pressure, temperature, and volume of gases based on molecular behavior.
• In micrometeorology, the process that involves the diffusion of water vapor and other gases is related to turbulent exchange in the boundary layer.

General Transfer Equation

• The symbol used to represent the vertical gradient of a property in the general transfer equation is typically denoted as ∂P/∂z.
• The downward flux of a property P in the general transfer equation depends on the gradient of that property, the diffusion coefficient, and the velocity field in the surrounding area.
• The mean square velocity of molecular motion in an ideal gas can be expressed using the formula: ( \langle v^2 \rangle = \frac{3kT}{m} ), where ( k ) is the Boltzmann constant, ( T ) is the temperature, and ( m ) is the mass of the gas molecules.

Momentum Transfer Representation

• In the context of momentum transfer, viscosity represents the resistance that materials experience when subjected to shear stress.
• The number of carriers moving towards one face of a cube at any instant in the general transfer equation is determined by the concentration gradient and the diffusion coefficient of the property in question.

This quiz covers topics related to the transport of heat, mass, and momentum in APHY 140 Lecture 5. It includes the general transfer equation, molecular transfer processes (momentum, viscosity, heat, thermal conductivity, mass transfer, and diffusivity), diffusion coefficients, and diffusion of particles through Brownian motion.