| Abstract: | An investigation has been conducted in order to fabricate, charge, model, and experimentally observe micro heat pipe arrays incorporated as an integral part of silicon wafers. Photolithography and anisotropic etching techniques have facilitated the fabrication of triangular micro heat pipes 120 μm wide and 84 μm deep. A successful charging technique has been developed which allows charging of a specific amount of the working fluid into micro heat pipes with a minimal amount of non-condensible gases. Steady-state experimental data of plain silicon wafers and those incorporating the micro heat pipe have confirmed the ability of these micro heat pipe arrays to improve the effective thermal conductivity of the plain silicon by as much as 45% at a heat flux input of 3.94 W/cm^2 and decrease the maximum temperature by 22.9°C at a heat flux input of 3.13 W/cm^2. Transient experimental data indicate that the incorporation of micro heat pipe arrays in silicon wafers retards the thermal response of the wafer though the exact nature of this interaction is not obvious. The affects of variations in the liquid charge have also been observed experimentally and studied analytically. Silicon wafers having heat pipe arrays with liquid charges of 50%, 30%, 20%, and 10% were fabricated. The optimal gains in effective thermal conductivity were observed for the wafer having the 50% charge value with a general trend observed of increasing thermal conductivity with increasing liquid charge. An analytical model of the capillary limit of a triangular micro heat pipe has also been developed. The model is the first to predict not only the capillary limit of triangular micro heat pipes fabricated in a silicon wafer, but also the capillary radius of the liquid/vapor interface in the evaporator as a function of input power. This model may be used to calculate the optimal liquid charge of a micro heat pipe as a function of input power... |
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