
24 Heat Transfer: Thermal Management of Electronics
It is impractical to calculate all these different modes of microscopic energies
individually. Instead, the total internal energy, denoted by U, is dened as the sum
of all these microscopic energies.
U =+++EEEE
translationrotationvibrationelectroonic nuclear
.+ E
(2.8)
Let’s dene a system as something identied for an engineering analysis. A system
may be an object such as the masses shown in Figures 2.2 and 2.3, the spring shown
in Figure 2.4, the gas inside the cylinder shown in Figure 2.5, the air inside a computer
chassis, an electrical resistor, or an integrated circuit. A system may also ...