Improvement of heat transfer within solar water heater’s tubes (SWH) using nanofluids

This research offers a numerical study of steady and laminar mixed convection flow in a circular pipe as part of a flat plate solar collector, which is crossed by nanofluids. The pipe is kept at a constant wall temperature and then at a constant heat flux, which represents the solar radiation received by the pipe. The governing coupled equations are solved with the finite volume approach. Computations are carried out using an in-house computer code, which has been satisfactorily validated by comparison to previous investigations. Empirical relations are used to predict the effective thermal conductivity and viscosity of nanofluids. The results are investigated using dynamic and thermal fields, with a special emphasis on the Nusselt number calculated along the active wall. They demonstrate that increasing the volume fraction of nanoparticles and Reynolds number improves heat transfer.