Thermal and hydraulic characteristics of a minichannel heat exchanger operated with a non-Newtonian hybrid nanofluid

In this study, thermal and hydraulic characteristics of a non-Newtonian hybrid nanofluid are investigated in a double-tube minichannel heat exchanger. The nanofluid contains two different nanoparticles, namely Tetra Methyl Ammonium Hydroxide (TMAH) coated Fe3O4 nanoparticles and Gum Arabic (GA) coated Carbon Nanotubes (CNTs). The nanofluid and water flow in the tube side and annulus side of the heat exchanger, respectively. Variable thermal conductivity and viscosity are applied in the simulations. Numerical solutions are performed based on both Reynolds number and mass flow rate, and the heat transfer rate in the heat exchanger, overall heat transfer coefficient, effectiveness, pressure drop, pumping power, and performance index are evaluated under different conditions. The results show that adding the nanoparticles causes a further increment in heat transfer rate at lower Reynolds numbers, such that the increase in heat transfer rate of the nanofluid compared with water at Reynolds numbers 500 and 2000 is 53.8% and 28.6%, respectively. The findings obtained show a promising view for use of this hybrid ferrofluid in mini heat exchangers. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.