Heat Sink 2
Category: Thermal Transfer
Define thermal radiation
Thermal radiation is the process of continual emission of infra-red waves from the surface of bodies, without the aid of a medium.
Define thermal convection
Thermal convection is the process of thermal energy transfer by means of currents in a fluid.
Define thermal conduction
Thermal conduction is the process of thermal energy transfer without any flow of material medium.
Describe in molecular terms, how thermal conduction occurs in a solid rod when one end of the rod is heated.
When one end of the solid rod gains heat, the heat energy absorbed is converted to kinetic energy in the rod particles. The particles at this end of the rod vibrated more vigorously in their fixed positions. The increased vibration is passed on to the neighbouring particles, causing the neighbouring particles to also vibrate more vigorously. Hence the increased vibration of the particles is passed on from particle to particle, till the particles at the other end of the rod also vibrate more vigorously.
When the average kinetic energy of the particles in the rod increases, the temperature of the rod increases. Heat energy is hence transferred from the hotter end of the rod to the cooler end of the rod through vibration of particles.
In metals, besides particle vibration, there is also electron diffusion to transfer the heat energy. The delocalised electrons are able to move more freely, hence heat conduction in metals is faster compared to non-metals.
Heat Sinks
a(i) Copper (or any metal).
Copper, being a metal, is a good conductor of heat. The heat generated by the electronic component will be conducted away at a faster rate by the heat sink, preventing the component from overheating.
ii) Black color.
Black colored surfaces are better emitter of radiant heat than bright colored surfaces. This will help the heat sink to emit its heat to the surroundings at a faster rate, so that the heat sink do not get too hot, and will still be able to gain heat from the electronic component effectively.
b)(i) 1W –> increase by 2 deg C
so 10W –> increase by 20 deg C
Answer: 20 deg C
b)(ii) As the temperature of the heat sink increase, the rate of heat conduction from electronic component will slow down, and the rate of heat radiated to surroundings will increase. Eventually, the rate of heat conducted into the heat sink will be equal to the rate of heat emitted from it. At this point, its temperature will remain constant.
Some ice cubes are added to a glass of water at room temperature. Describe in terms of density changes, how convection currents occur in the water to cause the water to cool down faster.
The water surrounding the ice cubes near the surface of the water lose heat to the ice cubes, contract and become denser.
The denser, cooler water then sinks downwards, causing the warmer, less dense water to rise upwards to take its place. This process repeats, setting up convection currents in the water, cooling down the water faster.