Basic Computer Thermodynamics
By Stephen Bucaro
That desk in front of you and everything else around you is made up of atoms. An
atom consists of electrons orbiting around a nucleus. An atom is increadibly tiny.
You could line up 10 million of them inside a millimeter. What if we could scale up
an atom so that the nucleus was the size of a basketball? The orbits of its electrons
would then be 15 miles away.
From this you can understand that atoms are almost all empty space. The nucleus of
the atom is composed of quarks. If you could see a quark or an electron up close, it
might appear as a tiny vibrating glow of energy. It turns out this world that is
causing us so many problems and so much stress is mostly an illusion!
The electrons orbit the nucleus at about the speed of light. If you could see them,
they might appear as a blur. They do not orbit in a plane like the pictures in books.
They create a shell. Sometimes two or more atoms will share electrons, causing them to
link together forming a molecule.
Looking at that desk in front of you again, it looks pretty solid. Actually, unless
your desk is floating in deep space where the temperature is close to absolute zero,
the molecules of your desk are vibrating like crazy. Picture the molecules bouncing
around and smacking into each other like balls on a pool table.
If you have ever played pool, you're very familiar with how when a pool ball hits
another pool ball, it transfers it's energy to the second pool ball. When heat causes
molecules to vibrate, they transfer energy between each other in a similar fashion.
This action is called "conduction".
Now picture the CPU of a computer cooking away because the designer wants to push
too much power through a small piece of silicon. If we don't take away that heat as
fast as it's created, that CPU will fry!
The problem is usually solved by mounting a heat sink on the CPU. Conduction causes
the heat to move from the hot CPU to the cooler heat sink. Because air doesn't conduct
heat as well as metal, We apply a thin layer of heat sink compound between the CPU and
the heat sink to fill in any gaps.
You'll notice that a heat sink has fins on it. The fins allow the heat sink to conduct
the heat to the air adjacent to the fins. The fins provide more surface area to aid in
conduction. Eventually the adjacent air will get as hot as the heat sink and conduction
If we move the air away from the heat sink, it will take the heat energy with it.
A fan mounted on the heat sink is used to move the air. This method of heat transfer
is called convection. Eventually all the air inside the computer case will get hot,
so fans are used to blow the air out of the case of the computer.
The heat has moved from the CPU, to the heat sink, to the air inside the case, to
the air in the room where you're sitting at your computer desk. The room starts to get
hot, and eventually the air conditioner turns on.
You can view an air conditioner as a "pipe". A fan blows the hot air from your room
through fins that transfer the heat to a liquid. The liquid is piped to fins outside
the house. A fan blows cooler outside air past the fins to remove the heat from the liquid.