PC case fans are used for keeping your PC cool no matter if you are air cooling or liquid cooling. They are used to bring cool air into your PC case and exhaust hot air from it. Alternatively, they are also used to dissipate heat from air coolers and liquid cooling radiators.
PC case fans are necessary to remove heat in most all custom cooled PC builds with the rare exception of passively cooled PCs. Important considerations are, fan diameter and thickness, noise levels, CFM, lighting, RPM, static pressure and PWM connections.
TITAN RIG offers a vast selection of PC case fans from all the top brands in a wide range of sizes, styles and price that are sure to work well in your custom cooled PC.