Heat Transfer Processes
Process Description Facts About
Conduction  Atomic or molecular kinetic energy (internal energy) is
 transferred between particles by collisions or close
 encounters. 
 Mathematically the rate is described by ΔQ/Δt = kA(ΔT/L) for
 heat flow through of rod of length L and cross sectional area A,
 the ends of which differ in temperature by ΔT, where ΔQ/Δt is
 the rate of heat flow (ΔQ being the amount of energy
 transported in time Δt) and k [W/m°C] is the thermal conductivity
 or heat conductivity of the substance of the rod.		  (1) Slowest of the three processes
 (2) Rate varies a great deal depending on the
       conducting substance.  May be thousands
       of times faster in some substances
       (conductors) than in other substances
       (insulators).
      
 (3) Rate is proportional to the temperature
       gradient.
 (4) Won't work in a vacuum.
Convection  Energy is transported by movement of a fluid (either a liquid or
 a gas).  The process occurs naturally in a fluid subject to
 gravity.  Convection in a horizontal direction is sometimes
 called "advection."		  (1) Won't work in either a vacuum or a solid.
 (2) The wind and ocean currents are nature's
       natural convection.
 (3) It may be driven mechanically by pumps (in a
       liquid) or fans (in a gas).
 (4) Is the most difficult to model or describe
       mathematically.
Radiation  Energy is transported by electromagnetic radiation (visible light
 and radiation of other wavelengths).  Each quantum of EM
 radiation ("photon") travels at the speed of light (c = 3 ´ 108 m/s)
 and carries an amount of energy equal to E = hc /λ, where
 h = 6.6261 ´ 10-34 Joule·second is Planck's constant and λ is
 the wavelength of the photon in meters.		  (1) Works best in a vacuum.
 (2) Won't work in an opaque medium.  Most
       mediums are of variable opacity to
       radiation of different wavelengths.  (Water
       vapor and carbon dioxide are both
       transparent to visible light but quite opaque
       to most infrared wavelengths.)
 (3) Is the means by which the sun's energy
       reaches the earth.