Fabrication and experimental investigation of silicon micro heat pipes for cooling electronics

An experimental investigation was conducted to determine the thermal behaviour of micro heat pipe (MHP) arrays micromachined in silicon wafers. Two types of MHP arrays were tested, one with triangular channels, 230 mum wide, 170 mum deep, and the other with triangular channels, 500 mum wide, 340 mum deep, coupled with arteries. Both types of arrays were fabricated using an anisotropic etching process. Once fabricated, a plain Si wafer was used to seal the pipe array hermetically. Two working fluids were tested, ethanol and methanol. A polysilicon heater was used to supply the heat input, and cooling water flowing through the condenser was used as a heat sink. Fill charges from 0% up to 66% were tested. The axial temperature variation along the length of the pipe was measured using T-type thermocouples connected to a data acquisition system. The effective thermal conductivity was evaluated using the experimental temperature profiles and 3D thermal modelling. The results show a maximum improvement of 300% in effective thermal conductivity at high heat flux, which demonstrates enhanced heat transfer in a prototype with liquid arteries.