Study of the Thermal Effectiveness of Laminar Forced Convection of Nanofluids for Liquid Cooling Applications

Recent theoretical studies show that the convective thermal performance of nanofluids in cooling applications depends crucially on the effective thermophysical properties and, if the performance comparisons are made under different flow constraints, contradictory conclusions can be drawn regarding the effectiveness of the same nanofluid. In this paper, an experimental study is reported on the laminar forced convection of Al₂O₃-water and Al₂O₃-polyalphaolefin nanofluids through a circular minichannel. With the experimental data, the thermal effectiveness of nanofluids is evaluated using various forms of figure of merit under three typical flow constraints, such as: 1) constant flow rate; 2) constant Reynolds number; and 3) constant pumping power. Although nanofluids enhance convective heat transfer, the results show that their thermal effectiveness is adversely offset by the combined effects of increased viscosity and lower specific heat. In particular, if a convective liquid cooling system is constrained by the constant pumping power condition, there will be essentially no difference in the overall effectiveness between nanofluids and the base fluid when both the thermal and hydrodynamic performances are considered.