10. Central processing units inside of modern desktop computers radiate consider
ID: 1397247 • Letter: 1
Question
10. Central processing units inside of modern desktop computers radiate considerable thermal energy. In order to cool the CPU effectively, a device known as a heatsink (or heat sink) is installed on top of the CPU to remove heat from the CPU quickly. Between the CPU and the heatsink, there is a conductive paste with a thermal conductivity of 0.94 W/m K. A fan forces air through the heatsink, cooling the heatsink to a constant temperature of 30 C Suppose the thickness of the thermal paste is 0.05 mm and the area of contact between the CPU and the heatsink is 260 mm (a) What must the temperature of the CPU be in order to transfer heat to the heatsink at a rate of 110 W? (b) When heat moves from the CPU, though the thermal paste, into the heat sink, is this an example of conduction, convection, or radiation? (c) When the air caries heat away from the heat sink and then out of the computer, is this heat primarily conduction, convection, or radiation?Explanation / Answer
a)
Rate of heat loss per unit area is proportional to the temperature gradient
Power/Area = K dT/dx
K thermal conductivity, dT is the temperature difference and dx is the thickness of the conductor.
dT = (Power x dx) / (K x Area).
= (110 x 0.05 x 10-3) / (0.94 x 260 x 10-6) = 22.5o C.
Temperature of the CPU = 30 + 22.5 = 52.5o C.
b)
This is an example of conduction, as the heat transfer involves direct contact between the substances.
c)
This is an example of convection since air acts as a medium to transfer heat indirectly
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