Valérie Sartre

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 μm wide, 170 μm deep, and the other with triangular channels, 500 μm wide, 340 μm 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.

Hydrodynamic and Thermal Study of a Water-Filled Micro- Heat-Pipe Array

A detailed mathematical model for predicting the heat transport capability and the temperature distribution along the axial direction of a 55-micro-heat-pipe array, filled with a polar fluid (water), has been developed. This steady-state model combines hydrodynamic flow equations with heat transfer equations in both the condensing and evaporating thin films. The velocity, pressure, and temperature distributions in the vapor and liquid phases are calculated. Various boundary conditions fixed to the micro-heat-pipe evaporator and condenser have been simulated to study the thermal performance of the micro-heat-pipe array below and above the capillary limit. The effect of the dryout or flooding phenomena on the micro-heat-pipe performance, according to boundary conditions and fluid fill charge, can also be predicted.