Thermal performance of a mini-channel heat exchanger (MCHE) working with CNT/GNP-based non-Newtonian nanofluids

In this work, the heat transfer of the non-Newtonian nanofluids inside a wavy microchannels heat exchanger (WMCHE) in cross-flow configuration has been experimentally and numerically studied. The Reynolds number (Re) does not have unique definition for non-Newtonian fluids. The non-Newtonian carboxyl methyl cellulose (CMC) aqueous solution containing 0.2 mass% CMC is used as base fluid (BF). The single-walled carbon nanotubes (CNT) and graphene nanoparticles (GNP) were added to the BF in 0.1 mass% as two other test fluids. Here, an equation based on the assumption of laminar flow is used in order to evaluate Re as a function of experimentally measured pressure drop. However, this assumption needs a similar form of friction factor relation to that of Newtonian fluids that is verified based on numerical simulation. In the presented work, finite element method (FEM) was utilized to perform the numerical modeling through Comsol Multiphysics software. Results show that as flowrate and relative waviness(2A/2L) increase, the convective heat transfer coefficient could be intensified. In terms of pressure drop, it was seen that with increasing the flowrate and relative waviness(2A/2L) of nanofluids, pressure drop was intensified. The results are compared to the experimental data and showed good agreement. The proposed performance index implies that GNP/BF nanofluid is the best one and both of two kinds of wavy configurations enhance the heat transfer efficiency, although the wavy two configurations are better.