Chip-level electronics cooling and diagnostics (infrared thermal velocimetry)

In this dissertation experimental results are presented for a CPL (capillary pumped loop) heat spreader and a micro-CPL which are developed for the cooling of electronic devices with high heat flux requirements. The CPL heat spreaders were made using grooved metal plates with a polyethylene porous matrix between them. The CPL heat spreader started automatically when the temperature of the evaporator increased to the saturation temperature corresponding to the reservoir pressure. For increased heating, dry-out of the CPL spreader occurred; when the heating load decreased below the dry-out heating load, the CPL spreader started again. The present copper CPL heat spreader has demonstrated a cooling capacity of 640W at atmospheric pressure in the vertical orientation and maintains a difference between T_IHE (temperature of the interface between the heater and the evaporator) and T_AMB (ambient temperature) that is lower than 100°C. However, starting of the micro-CPL was sometimes difficult; often it did not start because of the explosive bubble nucleation. To solve the starting problem, micro-pits were fabricated and tested. The results showed that these micro-pits enhanced bubble nucleation and resulted in less superheat. After the successful start-up, the maximum dry-out heating power of the current micro-CPL is then mainly limited by vapor bubble growth in the liquid line near the evaporator.; In addition, the measurement of the velocity is essential for the performance verification of many MEMS based fluidic devices. MEMS fluidic devices are mostly made of silicon. A new technique, infrared thermal velocimetry has been developed to measure velocity in silicon micro-channels utilizing the infrared transparency. Applications encompass MEMS fluidic devices with phase change and bio-fluidic elements where micro-DPIV (digital particle image velocimetry) can not be readily applied. An infrared laser was used to heat a fluid that was flowing in a silicon micro-channel transparent in the infrared range. Recording the resulting thermal images of the moving heated liquid yielded the velocity of the maximum radiative intensity point. The maximum velocity and the average velocity were obtained from the relationship between the measured velocity of the maximum radiative intensity point and the average velocity or the maximum velocity. This relationship can be obtained from either experiments or numerical simulation. (Abstract shortened by UMI.)...