Now for the more detailed explaination if you are interested.
We can consider most of the heat from a computer comes from the power supply and the CPU. The powersupply generally has its own fan which moves most of the heat out. The cpu moves most of its heat into air inside the computer via the heatsink and fan. This heat transfer is aided by having colder air inside your case.
For the case itself to actually transmit any heat, it would have to be warmer than the surroundings by several degrees. Since the motherboard is mostly insulated from the case, this requires the air to be several degrees higher than the case temperature to heat up the case, and if this is true, then your CPU's cooling is getting worse because the air it is using to cool is much hotter than air outside the case.
But assuming it does heat up to a few degrees above room temperature without melting your processor, then it would be cooling in a free convection environment, which doesn't work well at all (that is why you put a fan on your heatsink, to make it a forced convection environment).
You can easily see that making a case of aluminum will not make your computer any cooler. If you want it to run cooler, you need cooler air inside the computer. This makes your CPU's cooler work better, and carries heat from the rest of the computer away. To do this you need either a big, high flow case fan, or a window in the side of the case. And if you are going to waste money on either of these, just take off the side of your case.
This is something you can easily test. Start up your computer and let it run a few minutes, so that it heats up to its operating conditions. Then take off the side of the case. Unless you have it buried under in a tight spot where the airflow is likely to be no different than with the side of the case on, you will notice that your cpu will be a few degrees cooler. If you really want to see forced convection in action, go to Big Lots and get a cheap 8 dollar desk fan and point at your open case. It will run colder than you've ever seen.
But dont spend 200 dollars on a case thinking it will make your computer run cooler, because it won't. Aluminum does conduct heat better than steel and plastic of other cases, but it is limited by a convection environment on both sides, and it just wont transmit enough heat to be worth the money.
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Now for the more detailed explaination if you are interested.
We can consider most of the heat from a computer comes from the power supply and the CPU. The powersupply generally has its own fan which moves most of the heat out. The cpu moves most of its heat into air inside the computer via the heatsink and fan. This heat transfer is aided by having colder air inside your case.
For the case itself to actually transmit any heat, it would have to be warmer than the surroundings by several degrees. Since the motherboard is mostly insulated from the case, this requires the air to be several degrees higher than the case temperature to heat up the case, and if this is true, then your CPU's cooling is getting worse because the air it is using to cool is much hotter than air outside the case.
But assuming it does heat up to a few degrees above room temperature without melting your processor, then it would be cooling in a free convection environment, which doesn't work well at all (that is why you put a fan on your heatsink, to make it a forced convection environment).
You can easily see that making a case of aluminum will not make your computer any cooler. If you want it to run cooler, you need cooler air inside the computer. This makes your CPU's cooler work better, and carries heat from the rest of the computer away. To do this you need either a big, high flow case fan, or a window in the side of the case. And if you are going to waste money on either of these, just take off the side of your case.
This is something you can easily test. Start up your computer and let it run a few minutes, so that it heats up to its operating conditions. Then take off the side of the case. Unless you have it buried under in a tight spot where the airflow is likely to be no different than with the side of the case on, you will notice that your cpu will be a few degrees cooler. If you really want to see forced convection in action, go to Big Lots and get a cheap 8 dollar desk fan and point at your open case. It will run colder than you've ever seen.
But dont spend 200 dollars on a case thinking it will make your computer run cooler, because it won't. Aluminum does conduct heat better than steel and plastic of other cases, but it is limited by a convection environment on both sides, and it just wont transmit enough heat to be worth the money.
A word from a thermo guru:
An aluminum case shouldn't make much difference. Most of the heat put off by the computer is moved out by the case fan.