The application of a magnetic field tends to reduce the convective flows in enclosures, thereby decreasing convective heat transfer. However, adding nanoparticles to the fluid improves both thermal conductivity and viscosity, thus improving the conductive heat transfer. The enhanced total heat transfer is desirable in engineering problems like cooling systems for electronic devices. Therefore, the research for the best control of the pertinent parameters is a must. In this study, nanofluid convective heat transfer is investigated, seeking the best control of the governing parameters, namely, the Hartmann number 0≤Ha≤80, aspect ratio 0.25≤A≤4, and Al2O3 nanoparticle volume fraction 0≤φ≤0.05. Results show that the relationship between the heat transfer and nanoparticle volume fraction is different depending on A and Ha. In the absence of a magnetic field, there exists a critical value of A beyond which this relationship changes from enhancing to deteriorating heat transfer, whereas the application of a magnetic field leads to enhanced heat transfer with the use of nanofluids in horizontal enclosures which is due to the weakening effect on the flow that the magnetic field plays and leads to a strengthening effect of the nanofluid thermal conductivity over viscosity.
hadoui et al. (2026) studied this question.