Nanoparticles for heat transfer enhancement in microfluidic systems

Ever more packing of transistors into integrated circuits (ICs), in order to achieve higher processing powers, signifies the problem of cooling of hot spots, which are generated during the operation of these electronic systems. Without any proper thermal management, the temperatures of these hot spots can significantly rise, thus reducing the expected life and reliability of the ICs. Many methods have been introduced as cooling solutions for such hot spots, including those which use microfluidics. Thermal management using microfluidics is still facing substantial challenges. Conventional microfluidic based systems are not effective in cooling denser ICs as they are limited due to the general low thermal conductivity of conventional liquid coolants. It has been demonstrated that incorporating suspended nanoparticles in liquid, and forming the so called the “nanofluids”, enhanced the overall thermal conductivity of the liquid. However, still many issues yet to be addressed including a comprehensive understanding of the cooling effect in microfluidics, concentration limitation of the nanoparticles that cannot exceed 10% w/w, and the limitations posed by the materials used for making the microfluidic structure itself. In this research, the PhD candidate uses novel methods to tackle the aforementioned challenges for cooling hot spots using microfluidics. A novel infrared imaging method is used for a thorough understanding of the thermal effect of nanofluids in microfluidics. <br><br>In the first stage, the PhD candidate demonstrated the heat transfer analysis of thermally conductive alumina (Al2O3) nanoparticles suspended in distilled (DI) water for cooling a microfluidic channel. The thermal analysis of the suspensions was studied at various concentrations and at flow rates. The infrared camera, a non-contact device, allowed the observation of high resolution temperature profiling. In the second stage, the PhD candidate developed a novel concept to cool a hot spot in a microfluidic system based-on dynamically formed nanofin heat sinks from chromium oxide (CrO2) nano-rods using a magnetophoretic technique. CrO2 nanoparticles were chained and docked onto the hot spots; established tuneable high-aspect-ratio nanofins for exchanging heat between these hot spots and the liquid coolant. It showed that both high aspect ratio and flexibility of the nanofins had dramatic effects on increasing the heat sinking efficiency. In the third stage, the PhD candidate continued the previous work by investigating the nanofin heat sink structures using different morphologies of CrO2 and iron oxide (Fe2O3) magnetic nanoparticle. Results proved that the high thermal conductivity of the nanofins comprising CrO2 significantly enhanced the heat exchange across the microchannel. Additionally, the smaller size of Fe2O3 nanofins could transfer heat more efficiently in comparison to larger once. In the last stage, the PhD candidate introduced a solution for enhancing the thermal conductivity of polydimethysiloxane (PDMS) based microfluidics by introducing thermally conductive Al2O3 nanoparticles, forming PDMS/Al2O3 nanocomposites microfluidic systems. The nanocomposites were fully characterized for different concentrations of Al2O3 in PDMS. The outomes suggested that incorporation of Al2O3 at 10% w/w, significantly enhanced the heat conduction from hot spots, while maintaining the flexibility and decreasing the specific heat capacity of the developed materials.<br>