Research On Properties Of Direct Absorption Collector With Ionic Liquid Based Nanofluids

Solar thermal collector is one of the most popular and widespread techniques for solar energy utilization.The collector with excellent performance is the key to efficiently collect and solar energy into heat.The collectors are divided into direct solar thermal collectors and the traditional,we compare and analyze their respective advantages and disadvantages in this dissertation.We also summarize the limitations of traditional working fluids in the direct absorption solar collectors,and propose the nanotube/ionic liquid nanofluids are used in direct absorption solar collectors to obtain value-added high grade thermal energy.In this paper,without adding any surfactant,an ultrasonic method was used to homogeneously disperse the carbon nanotubes into the ionic liquid to prepare nanofluids with mass fractions of 0.04%,0.02%,0.01% and 0.005%.The thermal properties such as the stability and thermal conductivity of the nanofluids were measured by means of UV/Vis/IR spectrophotometers,liquid thermal conductivity testers,etc.The experimental results show that the nanofluids have great properties of dispersion and stability;Carbon nanotubes can significantly improve the thermal conductivity of the base fluid,and the larger the mass fraction of carbon nanotubes,the higher the thermal conductivity of the nanofluid,and the increase in temperature has little effect on it.The UV/Vis/IR spectrophotometer was used to test the solar absorption properties of ionic liquids and their nanofluids.Experiments show that the CNT/IL liquid nanofluid can effectively improve the solar absorption properties of the base fluid and the incident solar radiation can be completely absorbed by nanofluids.The above experiments verified the feasibility of ionic liquid-based nanofluids as a heat-collecting medium in a direct absorption solar collector.A mathematical model of the direct absorption solar collector is established.The distribution of the temperature field of the collector over time and the height of the collector is simulated by MATLAB software.On this basis,the relationship between collector efficiency and nanofluid mass fraction,nanofluid temperature and collector height was explored.The results show that the increase in the mass fraction of nanofluids does not increase the efficiency of the collector,but rather the efficiency of the collector is significantly reduced.Because the mass fraction of carbon nanotubes increases,the dispersed carbon nanotubes form a reflective surface that reflects a large amount of sunlight and reduces the efficiency of the collector.The higher the temperature rise of the nanofluid,the higher the secondary heat radiation of the nanofluids and the higher the natural convection heat loss on the receiver surface,and the heat loss of the collector leads the lower the efficiency;The increase in the height of the collector makes the temperature distribution more uniform,and can effectively increase the absorption of radiation in the full spectrum of sunlight and improve the efficiency of the receiver.These studies of solar collector systems and the design of dimensions are extremely important.This paper verifies that ionic liquids and nanofluids are suitable to be used as medium-high temperature heat-collecting medium in direct-absorption solar collectors,and the instantaneous heat collection efficiency can reach about 0.7,which provides a reference for the conversion of solar incident radiation into industrial high-grade heat energy.