I'm trying to design a cooling system for cooling nitrogen at 300°C. My original design (which is very open to modifications) is an aluminum ring block with exterior fins and vertical holes through the block connected end to end to form a continuously undulating gas line. An amazing engineer proposed flowing the gas through multiple holes simultaneously to address the pressure drop problem along the original single gas line, but any better approach is encouraged. My design operates by submerging the block into a water the size an Olympic swimming pool at 20°C. 468 g of nitrogen driven out of a vessel originally pressurized to ~5000 psi goes through the cooling system in roughly 10 seconds. The aim is to be able to cool the nitrogen down to 25°C as it exits the cooling system at that staggering flow rate.
What mass, geometry, and feature of the aluminum block, and/or modifications to the original design is required to achieve the stated aim.