Effect of Various Evaluation Criteria on Heat Transfer Enhancement of Nanofluids: A Case Study of Water-Based Cu2O Nanofluids

Abstract

The numerical study investigates the effect of various comparison criteria on the forced convective heat transfer of water-based cuprous oxide nanofluids in a horizontal mini tube under uniform heat flux conditions. The forced convective flow regime was validated, and it was ensured that the free convection effects were not present. The temperature-dependent thermophysical properties were considered for the numerical simulation. The volume concentrations of the nanofluids were kept below 2% (i.e., 0.6%, 1.3% and 1.9%) as higher concentrations lead to agglomeration and sedimentation of nanoparticles. The various comparison criteria employed for the assessment of heat transfer enhancement were equal pumping power, equal velocity, equal mass flow rate and equal Reynolds number criterion. The enhancements in heat transfer coefficient (at ϕv = 1.9% and base fluid Re = 1380) were 7.7%, 4.9%, 3.6% and 3.3% when assessed on the basis of equal Reynolds number, equal velocity, equal mass flow rate and equal pumping power, respectively. It was found that the enhanced heat transfer of the nanofluids should preferably be examined on the basis of equal pumping power criterion instead of above-mentioned other three criteria. The discussion on the invalidity of three evaluation criteria based on Reynolds number, velocity and mass flow rate has also been made.