Enhancement of solar energy collection with magnetic nanofluids

Nowadays, energy crisis has caused widespread concerns about sustainable energy. Solar energy, as sustainable, renewable energy, has attracted many attentions. Compared to other solar energy utilizations, solar collectors are more efficient and commercial devices to collect solar energy. In our present study, well-dispersed magnetic nanofluids (MNFs) are reported that they exhibit excellent optical thermal conversion performance under the suitable magnetic intensity and direction. In this work, the colloidal stability of MNFs was improved by controlling pH within neutral value. One kind of surface modifications, oleic acid, was carried out to enhance the interaction between particles and surfactants. The hydrodynamic diameter was found to be very close to the real size of particle. Meanwhile, a highly efficient solar collection system was built based on controlling the optical thermal performance of MNFs by magnetic fields. The experimental results showed that the thermal efficiency of solar collectors increased with MNFs. The thermal efficiency of MNFs is much higher than base liquid with the concentration of only 0.05 vol.%. Moreover, in the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough and 12% higher than the selective surface absorber. The study indicates that MNFs, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies. All these studies show the potential of MNFs in solar thermal conversion applications.