Investigating the Viscosity-Pressure Drop Trade-Off and Hydrodynamic Penalties in Nanofluid-Enhanced Cooling Loops

Abstract

This research explores the non-linear thermofluidic trade-offs in a thermal management loop for solid-state thermoelectric cooling (TEC) applications in the presence of nanoparticles. Although nanofluids convey a significant advantage in the convective heat transfer, the presence of a significant increase in dynamic viscosity of the nanofluid considerably limits its application, leading to an increase in pumping power. A stable Nanofluid of alumina-water ( ) with alpha phase alumina was synthesized using the two-step method with fixed ratio (1:1) using the stabilizer of Sodium Dodecylbenzene Sulfonate (SDBS). The Face-Centered Central Composite Design (CCD) was used to run 27 different parametric runs with a multi-variable experimental matrix. Three diameters of the nanoparticles (10 nm, 30 nm and 50 nm), three volume fractions (2.0%, 4.0% and 5.0% vol.), and three volumetric flow rates (0.5 L/min, 1.2 L/min and 2.4 L/min) were selected to encompass the laminar, transitional, and turbulent flow regimes. The performance of the system was determined by measuring the hot and cold junction temperature ( , ), system COP ( ), microchannel friction factors (fnf) and drop in core line pressure (ΔP). To minimize error, theoretical reduction models were used, such as Corcione's viscosity correlation and Leong's stationary nanolayer thermal reduction model. System level multi-objective optimization at a 2.36L/min flow rate was able to define a clear "sweet spot" envelope. The best combination is obtained when using 29.60 nm nanoparticles with a volume fraction of 4.18% vol., which leads to a minimum dynamic viscosity of 0.000891 , a well-controlled pressure drop of 10.52 Pa and maximized Performance Evaluation Criterion (PEC = 1.065). This empirical boundary shows that targeted particle nesting can be an effective way to avoid the large degradation of hydrodynamic performance at the hot-side thermal resistance limit (hydrodynamic degradation >5.0% vol.) and the clogging of the cooling loops by particles (clogging >5.0% vol.), and gives a clear mathematical recipe for reducing the hot-side thermal resistance without the hydrodynamic and clogging degradation.