How to cool down 4-5 KW of heat from the device packed into relatively tight place. My solution is air-cooling and precice airflow control.
All 4 nodes are housed inside the 24U closed rack. Cold air is sucked in near the floor at the bottom and pushed to the back side of closed rack. Then its sucked from back to front through GTX 295 GPU cards. Hot air isimmeadetly moved out from the rack, rising upwards to AC devices of the server room.
In the fan plate I use 3 x 170 mm diameter 240V AC fans at full speed.