Heat transfer and thermal efficiency of a lab-fabricated ferrofluid-based single-ended tube solar collector under the effect of magnetic field: An experimental study

Heat transfer and thermal efficiency of a single-ended all-glass evacuated tube solar collector (SEETSC), as a special type of heat exchanger in the solar thermal systems, can be improved using ferrofluids, as working fluid, under the effect of the magnetic field. The present experimental study investigates the natural convection, and thermal efficiency of a lab-fabricated ferrofluid (Mn-Zn Fe2O4/water) based single-ended tube solar collector, as a simplified model of the SEETSCs, in the presence of non-uniform magnetic field. Effect of the nanoparticles volume fraction (0.0-0.5%), input heat flux (q(in)''=50-350 W/m(2)) and the magnetic field generated by several identical permanent magnets (remanent magnetization (B-r) = 0.02-1.0 T) on the heat transfer and thermal efficiency of the collector is investigated. The results show that applying a magnetic field causes not only compensation of the heat transfer reduction due to the high viscosity values but also improvement of it. The maximum enhancements in the obtained average Nusselt number and thermal efficiency are respectively about 73.0% and 47.0% for the 0.5 vol% ferrofluid at q(in)'' = 350 W/m(2) and B-r = 1.0 T. According to this study, it can be feasible to enhance the thermal efficiency of the SEETSCs-based solar thermal systems using the ferrofluid under the effect of magnetic field.