Thermal and hydrodynamic performance of a microchannel heat sink with carbon nanotube nanofluids Effect of concentration and channel section

Increasing heat fluxes in decreasing sizes of a microchannel heat sink have necessitated studies into better systems, in particular a more capable coolant for improved thermal management. Nanofluids have been at the forefront with their higher thermal conductivity as compared to the base fluid alone. However, few investigations have looked into the role played by surfactants, a component used for dispersion and stability of nanofluids, and their influence on thermophysical properties and thermal performance. Optimized performances of carbon nanotube nanofluids with different surfactants at different volume fractions under laminar flow are studied. Using the thermal resistance model and experimental data for thermal conductivity and viscosity of nanofluids, the thermal resistance and pumping power are simultaneously minimized using multi-objective genetic algorithm. Results showed that the nanotube nanofluid with lignin as the surfactant performed better thermally and hydrodynamically, due to lower viscosity at high carbon nanotube concentration compared to the nanotube nanofluid with sodium polycarboxylate surfactant. As an example, a 29% and 28% increase in pressure drop is found for sodium polycarboxylate-based nanofluid at a volume fraction of 0.1% for a circular and square MCHS, respectively. A similar pattern is observed at higher volume fraction as well, even higher pressure drop with increasing volume fraction. Also, it is shown that microchannel heat sink with circular cross section performed better than that with square section.