An enclosure for an electronic system that is configured to act as a heat exchanger to remove heat from a cooling liquid that is circulated through the electronic system for cooling the electronic components thereof which are submerged in the cooling liquid in direct contact therewith. The enclosure uses an arrangement of a combination of external fins on one or more walls and fluid passages formed in one or more of the walls through which the cooling liquid is circulated for cooling. The fluid passages and the external fins are preferably formed on the same wall. The fins and the fluid passages can be formed on any number of walls of the enclosure.