HEAT TRANSFER ENHANCEMENT USING FERROFLUIDIC PLUG FLOW IN MICROCHANNELS
High powered electronic devices require very effective cooling to prevent overheating due to increased heat flux from their continued miniaturization. This is achievable using microchannel heat sinks capable of very high surface and volumetric heat transfer rates. Utilizing two-phase flow improves heat transfer by disrupting the inherent laminar flow within the microchannels via internal recirculation between the two phases. We focus on two-phase liquid-liquid plug flow using self-fabricated water-based ferrofluid plugs as the dispersed phase and silicone oil as the continuous phase. An external magnetic field is used to manipulate the magnetic plugs of fluid, providing greater disruption of the laminar flow than non-magnetic two-phase flow. Furthermore, the ferrofluid plugs allow for easy separation of the two phases for pumping. Experimental results show that microchannel heat transfer using ferrofluid plugs is superior to that using de-ionized water as the dispersed phase for two-phase liquid-liquid plug flow and demonstrates that cooling performance is further enhanced by the application of an external magnetic field, inducing mixing within the flow. We also visualized and theoretically predicted behavior of magnetic particle trajectory under the influence of an external magnetic field. Heat transfer rates can be increased by 2.7 times compared to single phase laminar flow (NuFF+OIL/NuDIW = 2.7). Heat transfer measured for ferrofluidic plug flow is expressed in terms of pumping power and compared to de-ionized water/silicone oil two-phase flow. This flow regime can then facilitate heat fluxes high enough (> 1000 W/cm2) to allow cooling of future high-power density power electronic devices.