Liquid metal based convective cooling systems
Creators: name: Zhu, Jiu Yang
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400899
subject: Electrical engineering not elsewhere classified
classificationCode: 401605
subject: Functional materials

description: Forced convection is one of the major mechanisms used for cooling of electronic systems. However, the problems associated with the size, fabrication, integration and maintenance of conventional convective cooling systems has limited utility of such technologies for thermal management of miniaturised electronic components. The existence of fluidic interfaces between the pump and the hot spot not only increases the footprint of the cooling system but also may cause additional problems such as the leakage of the coolant medium as well as reducing the response time of the pump. A new class of convective cooling systems, which can address these limitations can facilitate the generation of highly integrated electronic systems.<br><br>Gallium based liquid metal alloys have been recently used for making soft electronic and microfluidic devices. These alloys, which inherit the properties of both liquid and metal, have been utilised for making a new class of soft microfluidic elements such as pumps, mixers, valves, heaters and electrodes. These advances have motivated me to develop a novel class of liquid metal based convective cooling systems, which can be used for temperature regulation of both flow-through and flow-free systems in both static and dynamic modes.<br><br>As my first contribution, I demonstrated the utility of liquid metal pumps for the localised cooling of hot spots. These pumps, which consist of millimetre size liquid metal droplets, can be easily installed at desired locations of the system. Applying a low voltage square wave signal creates sufficient surface tension gradient across the droplet, providing a continuous flow of coolant medium through the cooling channel. The flow rate can be readily modulated by varying the frequency of the signal. Furthermore, the high thermal conductivity of liquid metal droplet allows it to serve as a heat sink, enhancing the dissipation of heat into the cooling channel. This hybrid pump-heat sink can reduce the temperature of localised hot spots, and has been characterised in various operating conditions.<br><br>As my second contribution, I demonstrated the unique features of liquid metal pumps for the transient cooling of hot spots. The elimination of mechanical moving elements and interconnecting tubes significantly reduces the response time of these pumps, enabling them to reduce the temperature of hot spots in a few seconds.<br><br>As my third contribution, I investigated the capability of liquid metal pumps for producing customised temperature profiles inside an isolated flow-free liquid chamber. A pair of liquid metal pumps is located along the opposite sides of the chamber to induce vortices inside the liquid chamber. The configuration and rotational velocity of the vortices can be easily modulated by varying the frequency of the signal. Customised temperature gradients can be produced inside the liquid chamber, breaking the inherent limitations of diffusive heat transfer in isolated chambers.<br><br>As my fourth contribution, I studied the ability of liquid metal pumps for creating controllable spatiotemporal temperature gradients inside an isolated liquid chamber. The rapid reconfiguration of vortices and the dominance of convective heat transfer enable the rapid change of temperature profile inside the chamber.<br><br>The versatility of liquid metal based convective cooling systems facilitates their incorporation into miniaturised yet highly integrated electronic devices. Accordingly, the simplicity and flexibility of such cooling systems enable their integration into the emerging soft and stretchable devices.