Design and investigation of a pulsating heat pipe for electronic cooling

Sammanfattning: The purpose of this study is to design and investigate a pulsating heat pipe device (PHP). A PHP is a two-phase flow heat transfer device which can handle high heat fluxes with passive internal flow. It is made of a continuous loop serpentine, partially filled with a working fluid that can cool systems, such as electronic devices. It differs from a conventional heat pipe device in design and operation, potentially bringing some advantages when compared to the latter. Firstly, no wick structure is required to assist the condensed working fluid to flow to the evaporator, making it cheap to construct and flexible to integrate into different applications. Secondly, more working fluid is used in a PHP, potentially enhancing heat transfer in it. The performance of a PHP can be measured by the thermal resistance, which is defined as the average temperature difference between the evaporation and condensation, divided by the supplied power to the device. The lower the thermal resistance, the more efficient the heat transfer in the PHP is. Despite the great efforts that many experimental and numerical works have put into fully understanding PHPs behaviour, since it was patented in the 90s, a lot remains unknown. This is mainly because of the chaotic two-phase, nonlinear internal flow of the device. In this thesis, after the initial stage of designing and manufacturing a glass PHP, investigating how different parameters affect the thermal resistance was conducted. This included testing the PHP performance while varying different filling ratios for different working fluids (isopropanol and distilled water), different inclination angles of the device, in addition to different supplied power levels to the PHP. Results, validated by previous similar conducted studies showed that the optimal filling ratio for the designed PHP ranged between 40%-70% for both tested fluids. With increased power supplies, the thermal resistance of the device decreased. When comparing the performance of both working fluids, isopropanol seemed to perform better in all working conditions compared to distilled water. As for the inclination, a PHP in vertical position (assisted by gravity), had a more stable pulsating motion. While when in horizontal position, the device failed to operate in a fully pulsating mode, making the designed demonstrator gravity dependent.