Heat transfer investigations of in-line conical strip inserts using MWCNT/water nanofluid under laminar flow condition

Abstract

The compound technique employed in forced convection system has proved the enhanced heat transfer through nanofluid and conical strip inserts in order to fabricate effective and reliable compact heat exchangers. In this investigation, Multi Walled Carbon Nanotubes (MWCNT)/De-ionized (DI) water nanofluid efficiently prepared and tested for three various concentrations (φ = 0.1, 0.25, and 0.5%) by two step method. MWCNT/DI water nanofluids through conical strip insert for three pitch ratios, Y = 2.5, Y = 3.5, and Y = 4.5 in a tube is experimentally studied for heat transfer and pressure drop, in the range of Reynolds number 540–2150 under constant wall heat flux. The higher volume fraction nanofluid φ = 0.5% and DI water with conical strip inserts were numerically studied. The contours of turbulence intensity, temperature, and pressure depict the flow phenomenon and heat transfer for in-line conical strips for the pitch ratios of 2.5, 3.5, and 4.5. As a consequence of local disturbance induced by these conical strips inserts intricacies, turbulence intensity increases along the test section. Simultaneously increase in fluid viscosity of MWCNT/DI water nanofluid enhances momentum and thermal diffusion. The result shows that the average deviations for Nusselt number is5% and friction factor is 9.1% between experimental and numerical results for the pitch ratio 2.5 at 0.5% volume fraction (VF) of MWCNT/DI water nanofluid. Nanofluid exhibits better performance than base fluid also conical inserts prompts higher Nusselt number ratio of 145%. This specifies MWCNT/DI water nanofluid with complex geometry of inserts could augment heat transfer considerably along with descent pressure drop. The obtained result shows that numerical readings are in good agreement with experimental readings. Even, the thermal performance factor found to be more than unity for all the cases, particularly it reveals that 1.90 and 2.01 for experimental and numerical results respectively for the pitch ratio 2.5 at 0.5% VF of nanofluid.