
34 Heat Transfer: Thermal Management of Electronics
W
A
is done on this system. Since the system is not insulated, heat may enter or
exit the system; we assume that heat Q
A
is transferring out of the system. Since
energy entering and leaving this system, the energy of system may change by
∆E
A
. If we choose gas B as our system, we will assume work W
B
is done by
this system and heat Q
B
is transferring out of the system and the energy of the
system changes by ∆E
B
. In the third choice for a system, gas A and B together,
there is no work done on the system as the cylinder does not change volume
but heat Q may enter that system and its energy may change ...