Experimental study on the heat transfer and pressure drop of oil-based nanofluids in laminar flow inside horizontal tubes

An experimental investigation was carried out to study the convection heat transfer and pressure drop of oil-based multi-walled carbon nanotube nanofluids. The necessary data were acquired for laminar flow in the thermal entrance region. Nanofluids were produced at different mass concentrations (0.005%, 0.010% and 0.015%) using the two-step method. The thermophysical properties of nanofluids, thermal conductivity, viscosity and density, were experimentally measured. A surface treatment of the nanoparticles using oleic acid was performed. The stability of nanofluids was estimated with a UV–VIS spectrophotometer. The results of the heat transfer coefficient revealed increments with the presence of carbon nanotubes. Regarding the pressure drop, the experimental results suggested slight increases with the addition of particles. The results of UV–VIS spectrophotometry demonstrate that nanofluids with surface treatment of nanoparticles have better stability when compared to nanofluids without surface treatment. Finally, a figure of merit was proposed to evaluate the results obtained, which relates the increase in heat transfer as a function of the increase in pumping power.