Whenever I upgrade a computer, I always try to salvage and reuse as many of the old parts that I can. One part that I have collected a lot of over the years is the cooling fan. You find these in power supplies, on CPU's and in tower cooling systems.
So what do you do with a bunch of small fans? You combine them into one big fan. In this project I take 16 PC cooling fans and mount them together to make a single 12 volt box fan. It is thin, light weight, strong, and quiet. It also stores easily. It can fit behind furniture or in a packed car. It can be powered by your computer's power supply, an AC adapter, or a 12 volt car battery.
For step by step instructions, check out the instructable: