Development of new correlation for convective heat transfer in horizontal heated tubes using Fe ₃ O ₄ /water nanofluids under turbulent flow: an experimental study

This study experimentally explores the turbulent forced convective heat transfer characteristics of Fe3O4/water nanofluids in a horizontal circular tube, with a novel focus on applying a constant electrical heating power of 420 W – an approach that closely simulates practical thermal systems. Nanoparticles averaging 10 nm in diameter were used at low volume concentrations ranging from 0% to 1.4%, and tests were conducted over a wide Reynolds number range (2700 to 11,000), encompassing both low and high turbulent flow regimes. The results revealed a clear enhancement in heat transfer performance with increasing nanoparticle concentration, with Nusselt number improvements of approximately 7%, 21%, and 45% for 0.35%, 0.7%, and 1.4% concentrations, respectively, compared to pure water. A significant contribution of this work is the development of a new empirical correlation for predicting the Nusselt number in turbulent flow, validated with a maximum error margin of ±10%. The novelty of this study lies in its comprehensive experimental coverage under realistic heating conditions, the use of stable, ultra-fine nanoparticles, and the introduction of a reliable predictive model – providing valuable insights for the design of advanced thermal systems utilizing Fe3O4 nanofluids.