Lecture 1 Flashcards
Intro to biotransports
What are transport phenomena
They describe the movement of mass, momentum, energy and electrical charge
Mass transfer & driving force & ex
Done through diffusion with concentration gradient as a driving force
Drug delivery, nutrient and molecular transport for cell metabolism, exchange of molecules across membranes
Diffusion
mvm of molecular species through random collisions
Convection
Transport of momentum by bulk fluid motion causing velocity differences between layers causing momentum transfer
Viscocity
Frictional resistance to flow
Can be thought of as a measure of the rate of momentum transfer between layers of fluid
Momentum transfer driving force + ex
Done by convection, driving force: velocity gradient
ex: biofluids, drug delivery, biomedical devices (lung-heart pump)
Heat transfer
Done through heat conduction, convection or radiation
Driving force: temperature gradient
Examples: sweating, biomedical (cryogenic freezing)
Heat conduction
transfer of energy through molecular collisions
Heat convection
Transfer of energy through fluid motion
Radiation
Radiation: Transfer of energy through electromagnetic waves
System, environment
System: portion of the universe directly involved with a particular process
Environment: rest of the universe
Boundary
Boundary: Interface between system and universe
Closed vs open system
Closed system has fixed mass (but E can change)
Open system has exchange of mass and energy across its boundary
Intensive vs extensive properties
Intensive properties are independant on size of the system
- Temp, density, viscosity, diffusivity, thermal conductivity, pressure?
Extensive properties depend on system size
- mass, heat, volume, momentum
- Can flow in and out of the system
Density in continuum
Mass per unit volume as volume approaches zero
Conservation equation
Within a system: Rate of accumulation = Net rate of production + Net rate of quantity entering system boundary
System in equilibrium vs not
Equilibrium with environment = no net change in extensive properties or spatial variations in temp and pressure
Not: driving force (gradient) causing flow
Constitutive relationship for molecular transport mechanisms
Empirical equation relating motion of an extensive property (mass, heat, volume, momentum) with the negative gradient of an intensive property (conc, temp, velocity)
Flux
Amount of an extensive property X passing through a unit area A (perpendicular to n direction of flux) per unit time
Vector
Gradient and potential
Potential: Intensive property (concentration, temperature,
velocity) inducing flux of X.
Gradient of the potential: Rate at which the potential varies in the n-direction at that point
Scalar
Constitutive property
ability of a material to facilitate the transport process
Ex: viscosity, diffusivity, thermal conductivity
Whats molar volume and how to relate it to volume
Vm (m^3/mol) = Molecular weight (g/mol) / density (kg/m^2)
Volume = n (mols) * Vm (m^3/mol)
Whats denstiy equation and the continuum equation rules
density at a pt (x, y, z) = lim deltaV -> delV of delta m/ delta V
del V = smallest volume at which we can ignore molecular nature of the material and preserve the concept of density
If the delta V we are looking at is larger than the critical volume del V then delta V is a continuum and not too small for density to be uniform
