Thermal performance of a pulsating heat pipe charged with Fe3O4-MWCNTs/DI water hybrid nanofluid: Experimental study and optimization

In this study, we have employed a strategy for the optimization of the concentrations of iron oxide ( Fe 3 O 4 )-multi-walled carbon nanotubes (MWCNTs)/deionized (DI) water hybrid nanofluid based on non-dominated sorting genetic algorithm-II (NSGA-II) before examining it inside the pulsating heat pipe (PHP), taking into account the basic criteria for PHP performance optimization. The thermophysical properties of the hybrid fluid were optimized to obtain concentrations with the highest thermal conductivity and specific heat capacity and the lowest dynamic viscosity and density. Also, the thermal performance of the PHP charged with the optimized concentrations of the hybrid nanofluid was tested. Results showed that the hybrid nanofluid containing 0.597 vol . % of Fe 3 O 4 and 0.100 vol % of MWCNTs provides the best thermal performance for the PHP. Further, the thermal performance of the PHP with base fluid (DI water) was tested. The observations indicated a better start-up and a lower thermal resistance of the PHP with DI water. The thermal resistance of the PHP charged with mentioned hybrid nanofluid and DI water at a heat input of 70 W is 0.185 ∘ C W - 1 , which is almost 49.45 % lower than that of PHP charged with other hybrid nanofluids. Therefore, it can be concluded that although the Fe 3 O 4 -MWCNTs/DI water hybrid nanofluid has a relatively high thermal conductivity, its high viscosity, low specific heat capacity, and sedimentation of the nanoparticles deteriorate the thermal performance of the PHP compared to the base fluid due to increased concentration.