Loop heat pipe technology for cooling computer servers

An air cooled loop heat pipe (LHP) system was developed for cooling a dual CPU 1U server. The LHP uses newly developed flat plate evaporators and air cooled condensers with millimeter scale condensation channels and plain parallel fins. Bench tests were conducted using 20 x 20 mm uniform heat sources dissipating 100 watts and air preheating to simulate air-cooled operation within a 1U server chassis. Thermal resistance was decreased as the air temperature increased from 25degC to 50degC. At 50degC air temperature, the LHP evaporator surface temperature reached 65degC showing an effective evaporator surface to air thermal resistance of 0.15degC/W. A commercial 1U server with dual 100 W rated Intel Xeon processors was used to compare the effectiveness of the LHP cooling system to the standard processor fan heat sinks. Multiple instances of CPU Burn were used to exercise the CPU´s for maximum power dissipation. Under similar test conditions with room air temperature in the range 26-30degC, the interface temperature at the processors stabilized at ~75degC with the fan heat sinks and ~55degC with the LHP cooling system.