This is an easy to build air amplifier for 12cm case fan. It uses the same principle as the Dyson air multiplier. Low pressure air is sucked in through the small holes in the fan duct creating a stronger airflow.
Parts:120mm fanhttps://www.banggood.com/custlink/mDmmqlYRWT
fan mount screw x 4https://www.banggood.com/custlink/DmGKUoyYVK
3mm screw and nut
12v battery or power supply