RESUMO

Forced convective heat transfer studies on DIW-based Ni-substituted MgMn nanoferrofluids flowing through straight tubes and helical coils under laminar flow and constant wall temperature conditions have been conducted. A transformer oil/deionized water mixture (60:40 by wt.%) was used as the base fluid and nanoferrofluids with nickel-substituted magnesium manganese ferrite nanoparticle volume concentration of 0.6% and 0.4% were used as the working fluids. Results showed that the convective heat transfer coefficient of the nanoferrofluid was higher than that of the base fluid for both straight tubes and helical coils. In a straight tube, Nusselt number enhancement was 25 with respect to the base fluid and it increased to 39% with increase in the Peclet number from 45,000 to 112,400 for the nanoferrofluid having volume concentration of 0.6%. While in helical coils, maximum enhancement in the experimental Nusselt number was found to be 26.5% and 29% at volume concentrations of 0.4% and 0.6%, respectively, for a curvature ratio of 0.0727 corresponding to a Dean number of 490. Two new correlations have been proposed to predict the heat transfer coefficient of nickel-substituted magnesium manganese nanoferrofluid flowing under laminar conditions through a straight tube and helical coils.