Heat transfer and pressure drop investigation through pipe with different shapes using different types of nanofluids

In the present study, the heat transfer and hydrodynamic analysis of flow through single-pipe heat exchangers of circular and square cross-sectional configurations were performed. The experimental and numerical investigations were conducted to evaluate the performance of two metallic oxides (Al₂O₃ and SiO₂) and two carbon-based nanostructured nanofluids (KRG and GNP) in comparison with the distilled water (DW). The data obtained from the experimental runs with DW as a working fluid in both test sections were used to validate the 3-D numerical models for the square and circular pipe heat exchangers. The flow in both test sections is considered as a fully developed turbulent flow with the Reynolds number range of 6000–11,000, and both the test sections were subjected to a uniform heat flux at their outer surfaces. The concentrations of all nanofluids used in the present study were in the range of (0.025–0.1 mass%). The test rig was firstly validated during the water run by using different empirical correlations for the evaluation of pressure drop and Nusselt number and showing a very good agreement, and then, the numerical models were validated with the data obtained experimentally and the errors were less than 10% for both models. For the square tube flow, the average errors between the numerical and experimental findings of Nusselt number and pressure drop were 6.8% and 2.49%, respectively, and for the circular pipe flow, the evaluated errors were 9.34% and 5.92% for Nusselt number and pressure drop, respectively. The performance index for all the nanofluids was calculated to obtain the convective heat transfer coefficients and friction losses of the fluids in both the tubes. The results showed that the non-covalent graphene–DW is not suitable for heat transfer applications due to its higher viscosity. The results also showed a different enhancement of heat transfer for the same nanofluid in circular and square tube flows, whereas the performance index of the same nanofluid appears nearly the same for flow through both the cross sections.