Thermal Conductivity
Heat is transferred along a material by collisions from molecule to molecule. This form of heat transfer is called heat conduction.
Let's consider a bar having a length L and a cross sectional area, A. One end of the bar is kept at a hot temperature T2 , the other end is at a cold temperature T1. The
heat transfer rate (amount of heat transferred per unit time) ΔQ/ Δt is proportional to the difference in temperature, ΔT,
between the two sides of the bar.
ΔQ/ Δt =KA (T2 –T1)/L
K is defined as thermal conductivity and is a material property.
It has units of Watts per meter per degree C.
(T2 - T1)/L is also called temperature gradient and is the "driving force"
Heat conductors (such as metals) have a large value of K, heat insulators (such as wood, brick) have a low value of K. This is the reason why houses are
made of wood and brick (to keep us warm) and for example the heat sink of a CPU is made of aluminum (to be an efficient hear extractor!)
Continue...
Home page Back to topic ........ Previous page ......... Next page
|
