An improved apparatus is disclosed for cooling the power dissipating components of a computer subsystem, including microprocessors and hard disk drive assemblies. The apparatus utilizes the computer subsystem's chassis or enclosure, by configuring it as a roll bond panel formed from two sheets bonded together to define a fluid channel therebetween. Various concentrated sources of power dissipation are mounted within the enclosure on special component panels that themselves define a fluid channel. A working fluid is disposed within the channels of the component panels and the enclosure panel. During operation, heat generated by the sources of power dissipation is transferred to the working liquid within the fluid channels of the component panels and, in turn, to the working fluid disposed within the fluid channel of the enclosure panel, for dissipation by convection. In one disclosed embodiment, the working fluid undergoes a reversible phase change, to facilitate an efficient transfer of heat throughout the enclosure panel and thereby to heat the panel to a substantially uniform temperature.