A portable, self-contained liquid submersion cooling system that is suitable for cooling a number of electronic devices, including cooling heat-generating components in computer systems and other systems that use electronic, heat-generating components. The electronic device includes a housing having an interior space, a dielectric cooling liquid in the interior space, a heat-generating electronic component disposed within the space and submerged in the dielectric cooling liquid, and a pump for pumping the liquid into and out of the space, to and from a heat exchanger that is fixed to the housing outside the interior space. The heat exchanger includes a cooling liquid inlet, a cooling liquid outlet, and a flow path for cooling liquid therethrough from the cooling liquid inlet to the cooling liquid outlet. An air-moving device such as a fan can be used to blow air across the heat exchanger to increase heat transfer.