ABSTRACT
Heat is energy transferred between materials due to tem-
perature differences (e.g., different amounts of internal
energy). There are three mechanisms that are responsible
for thermal energy transfer: convection, conduction, and
radiation. These mechanisms can occur individually or in
combination. An example of a situation where all three
mechanisms occur is heat being conducted through
a double pane window, Fig. 1. On the outside of the
window, air transfers heat by convection to the window
glass. Conduction transfers the energy through the glass.
On the inside surface of the glass, energy (heat) is radiated
between the two glass panes and is also conducted
through the air filled gap. Conduction occurs instead of
convection because the air gap is small and convection
currents cannot develop. The energy is then conducted
through this window glass to the inside of the room.
Convection then transfers the energy away from the
glass warming the room air. The direction of energy
transfer (heat) is always from high temperature (warm)
to low temperature (cold).
