Oscillating Heat Pipe Performance with Evaporator Section Modifications

The continuous development of electronic components to become faster and smaller has led to an increasing problem with thermal management. Thermal management ensures that the component operating temperatures are within a safe range, which maintains performance and improves reliability and lifespan. Traditional thermal management devices, such as the extruded-fin heat sink, are incapable of maintaining the safe operating temperature range for current and future high heat flux cooling applications. A device that has the capability to meet this growing need is the oscillating heat pipe. Oscillating heat pipes (OHPs) are passive, two-phase cooling devices that have been shown to transfer very large amounts of thermal energy over large distances, resulting in low thermal resistances. OHPs consist of two main sections: the condenser and evaporator that are interconnected by looping channels. The channels are filled with a two-phase mixture of acetone, which acts as the heat transfer medium for the system. In this study, geometric features in the evaporator section are compared to determine operational effects. Four OHP evaporator geometries are compared: traditional straight-channels, pin-and-cavity channels, recessed-cavities, and wavy-channels. Each OHP is constructed from a flat aluminum plate with 22 interconnected 2-mm × 2-mm square channels. These geometries were tested at 35%, 55%, and 75% fill ratios and at vertical, 45°, and horizontal inclination angles. It was found that the wavy-channel, straight-channel, recessed-cavity, and pin-and-cavity OHPs had an overall thermal resistance of 0.32 K/W, 0.49 K/W, 0.37 K/W, and 0.60 K/W, respectively. This corresponds to a 41% and 28% improvement for the wavy-channel and recessed-cavity OHPs, and a 30% reduction in performance for the pin-and-cavity OHP. The wavy–channel OHP was the only geometry that was fully functional in the horizontal orientation, achieving an average thermal resistance of 0.17 K/W with a 55% fill ratio. The recessed-cavity OHP preformed the best above horizontal, where an average thermal resistance of 0.18 K/W was found. The best thermal resistance was 0.11 K/W by the recessed-cavity OHP at vertical orientation and 35% fill ratio. The wavy-channel and recessed-cavity OHPs both showed significant improvements over straight-channel and pin-and-cavity geometries. This indicates that geometric variations can be integrated into OHP designs to improve system performance