Experimental study and CFD modelling on the thermal and flow behavior of EG/water ZnO nanofluid in multiport mini channels

Highlights: • The thermal and flow behavior of EG/water ZnO nanofluid were studied. • Influences of concentration, channel dimeter and heat load were studied. • A new correlation for Nusselt number was proposed. • CFD simulation using single-phase and mixture model was conducted. Nanofluid and mini channel are two promising approaches to enhance the heat transfer performance. The present study combined these two techniques together and investigated the heat transfer and flow behavior of ZnO ethylene glycol (EG)/water nanofluid inside two multiport mini channels with the hydraulic diameters of 1.22 mm and 1.42 mm. ZnO nanoparticles with an average diameter of 30 nm were dispersed into 40%/60% EG/water solution to get nanofluids with 0.75% and 1.5% volume concentration. The heat transfer and flow performance under various operational conditions were identified by both experiments and CFD simulation. Experimentally, it reveals that the Nusselt numbers are averagely improved by 6.7% and 9.8% for nanofluids with 0.75% and 1.5% concentration respectively. However, the friction factors are also enlarged by 4.6% and 8.6% correspondingly, which results to a various thermal performance factor ranging from 0.94 to 1.31 with the average values of 1.05 and 1.07. The decrement of channel diameter leads to greater heat transfer coefficients, pressure drop, friction factor but nearly the same Nusselt number. A new correlation is developed to predict the Nusselt number for ZnO nanofluid flow in multiport mini channels with a MARD of 9.2%. Numerically, single-phase model gives better predictions for both Nusselt number and friction factor with the average relative deviations of nearly 16% and 19.1% correspondingly. Mixture model severely overestimates the Nusselt number but shows a reasonable friction factor prediction. The present study is expected to give some guidance for the study of nanofluid in mini channels.