The design and testing of the super fiber heat pipes for electronics cooling applications

Cooling of electronics is one of the major fields of application for heat pipes (3-9-mm outside diameter) with a worldwide demand exceeding one million per month. The high heat fluxes associated with electronics cooling require heat pipes with high maximum heat transfer at any inclination, and therefore improved wick structures are needed. In particular, the operation at top heat mode (vertical orientation) is required by most notebook manufacturers with a decrease of 30%-50% of the thermal resistance over conventional systems. A new wick structure has been developed so the capillary channels are increased with small effects on the heat pipe permeability. Using this new design criterion, (which balances the permeability and capillary needs), super fiber bundle heat pipes have been developed. The diameter of the wire used in the fabrication varied from 0.05 to 0.1 mm and the maximum input power was 16 W. It was found that the vapor space/liquid space ratio is an important parameter for this type of heat pipe. The test results show that the thermal resistance of the heat pipes is a strong function of the orientation. We have fabricated heat pipes with two to five times lower thermal resistance than previous conventional heat pipes (for the top heat mode operation). A comparison with other types of wick structures is also presented. Thermal resistances as low as 0.5°C/W (top heat mode) and 0.2°C/W (horizontal operation) have been observed. The application to electronics cooling it has been successful, especially in notebook computers and telecommunications applications