When you open the case of a desktop computer, you see some dust, especially around the fans. What can you use to clean the fans out?

Using an enclosure, which is basically an extra case, is one approach to keep dust and debris out of your computer. However, using compressed air instead of vacuuming is the best approach to get rid of dust and debris if they do get inside your case. In contrast to a vacuum could, compressed air is easier to direct and doesn't frequently result in ESD damage. Simply use a stream of compressed air to blow the dust out of the computer. Make sure to do this outside to avoid blowing dust all over your workspace or yourself, and place a pen or pencil in the fan so it won't spin while you're dusting it off. Because denatured isopropyl alcohol dries quickly, it is used to clean contacts. Demineralized water would not be utilized within the case, with the possible exception of a liquid cooling system.