Cooling of CPU with a thermosyphon

In this study the tested evaporator is made from small blocks of copper with 11 vertical channels with a diameter of 2.5 mm and length of 30 mm. The riser and downcomer connected the evaporator to the condenser, which is cooled by air in free or forced convection. The condenser is made from 10 mm aluminium heat sink profile of the size of 365times365 mm with a fin length of 20 mm at a distance of 8 mm. In the top part of the heat sink a condenser channel system with 2times2 mm cross section is milled. The CPU used in this study is an Intel Pentium 4 with 3.2 GHz. The maximum heat load to the processor is 104 W, and the highest temperature allowed on the processor is 65degC. Temperatures are measured for idle, 50% and maximum heat load of the processor at the CPU, evaporator wall, condenser wall and in the ambient. Temperature differences in the thermosyphon system, between the CPU and the evaporator wall, the condenser wall and ambient are presented. Isobutane has been used as the working fluid, due to the fact that it has low saturation pressure and that this refrigerant is friendly to the environment.