Investigation of applying nanoporous graphene non-Newtonian nanofluid on rheological properties and thermal performance in a turbulent annular flow with perforated baffles

In this work, the convection heat transfer and pressure drop of the turbulent flow for a non-Newtonian fluid containing nanoporous graphene were investigated in baffled heated annulus tube by considering the inner tube under constant heat flux. The solution of 0.2 mass% carboxymethyl cellulose (CMC) in DI water was used as the base non-Newtonian fluid. The rheological properties of the nanofluid (0.2 mass% nanoporous graphene, 0.2 mass% CMC and DI water) were measured through an experimental setup. By measuring the thermophysical and rheological properties at several temperatures, the temperature-dependent equations were calculated by a least square approximation method. By using the extracted equations and adding the nanoporous graphene to the base fluid in the annulus, the thermal performance was numerically investigated. Furthermore, the effects of the geometry and perforated baffles number at the various Reynolds numbers were studied. According to the results, the nanoporous graphene had a significant effect on the average Nusselt number and pressure drop which were increased by up to 32 and 75%, respectively, compared to the base fluid. It was also predicted that in the annular tubes possessing three and seven baffles with four holes (Re = 4000 and H = 4 mm), applying nanoporous graphene can improve the efficiency of the system up to 11.9%.