Preparation And Properties Of Carbide Photo-thermal Conversion Nanofluids

Fossil energy crisis and environmental pollution are the most serious worldwide problems.It is the top priority to find clean energy to replace fossil energy.Solar energy is easy to obtain,abundant,clean and safe,and environmentally friendly,thus it becomes the focus of researches.Nanofluids have a great prospect in photo-thermal utilization.The researches on the preparation and properties of photo-thermal conversion nanofluids have great significance for the utilization of solar energy.In this paper,ZrC aqueous nanofluids were prepared by dispersion method.The composition and morphology of the ZrC nano-particles were characterized by XRD and TEM.The stability of the prepared nanofluids was studied by a sedimentation method.A photo-thermal conversion property evaluation device was established,and the calculation method of photo-thermal conversion efficiency was improved.The optical absorption and photo-thermal conversion properties of the prepared nanofluids were studied.The results show that,when the ultrasonic time is 30 minutes and the mass fraction of PVP dispersant is 8-10% of zirconium carbide,the stability of ZrC nanofluids is the best.The transmittance of nanofluids decreases with the increase of solid content.When the optical path is 1cm,the 0.02 wt% ZrC nanofluids absorb sunlight almost completely,giving a solar weighted absorption coefficient Am of 0.99.The maximum temperature rise of the 0.02 wt% ZrC nanofluids is 38.2 ? under the simulated sunlight conditions,and the photo-thermal conversion efficiency is 92%.This method of efficiency calculation takes into account the loss of heat,thus it can evaluate the photo-thermal conversion properties of nanofluids more rationally.WC aqueous nanofluids were prepared by a grinding method.The effects of dispersant species and their amount on the stability of nanofluids were studied.The optical absorption and photo-thermal conversion properties of the nanofluids were studied.The results show that,stable nanofluids can be obtained by using 2 wt% PVA as dispersant.The optical absorption of the WC nanofluids increases with the increase of solid content.When the optical path is 1 cm,Am of 0.3 wt% WC nanofluids is 0.99.The maximum temperature rise of 0.3 wt% WC nanofluids is 39.5 ? under the simulated sunlight conditions,and the photo-thermal conversion efficiency is 97%.The WC nanofluids can be regarded as ideal solar energy absorbers.A solar evaporation test device was established using WC nanofluids as the photo-thermal conversion media.The solar energy utilization was enhanced by the local heating of the nanofluids.The evaporation efficiency was improved by increasing the concentration of the nanofluids.Compared to the integral evaporation of pure water,the evaporation capacity and evaporation rate were increased significantly.The evaporation rate was 1.53 kg·m-2·h-1 by using 0.3 wt% WC nanofluids as heating medium and the evaporation efficiency was increased by 23%.It provides new strategy for solar water evaporation and seawater desalination.Both ZrC and WC nanofluids exhibit broad band absorption characteristics,which can significantly enhance the absorption of solar radiation.The current work is of great significant to application of photo-thermal conversion nanofluids in the field of solar energy utilization.