Study Of Solar Radiation Absorption Properties And Collection Feasibility Of Nanofluids

Because of the dispersed nanoparticles, the radiation absorption and heat transfer properties of nanofluids are different from those of the base fluid, becoming an efficient absorbing material. A kind of direct solar collection system using collector tubes without coating, in which heat transfer oil added with nanoparticles as the absorbing and heat transfer medium was proposed and studied.Firstly, the transmissivity and extinction coefficient of the nanofluids added with different nanoparticles and mass fraction were tested by spectrophotometer. And the effect of mass fraction and nanoparticles on full spectrum radiation absorption properties of nanofluids was also studied. The absorption coefficient of heat transfer oil-based CuO nanofluids with different mass fraction was tested by integrating sphere and the influence of scattering of nanoparticles on the absorption property was analyzed. Results show that compared with the base fluid, nanofluid has better radiation absorption property, which is closely related to the mass fraction.Secondly, the heat transfer models of nanofluid-based direct absorption solar collection (NDASC) and indirect absorption solar collection (IASC) were developed. The thermal performance of NDASC and IASC under different operation condition was compared by numerical simulation and experiment. Results show that compared with IASC, there is a specific critical temperature for NDASC under each operation condition. The specific critical temperature is the maximum operating temperature for NDASC, where the collection efficiency of NDASC is higher than that of IASC with the same structure size. In addition, the specific critical temperature increases with the increase of concentration ratio and solar radiation intensity.In addition, two novel types of solar collectors were studied, which were NDASC with heat pipe and NDASC with U-shaped tube. The heat transfer models of NDASC with heat pipe and NDASC with U-shaped tube were developed. The effect of collector structure and solar radiation intensity on the temperature distribution characteristics of nanofluids were simulated by CFD. Results shows that compared with IASC, NDASC has higher mainstream center temperature and collection efficiency.The collection efficiency of NDASC with heat pipe and NDASC with U-shaped tube increases with the increase of solar radiation intensity and pipe diameter. Besides, the experimental system was set up to investigate the collection efficiency of NDASC with heat pipe and IASC with heat pipe. Experimental results show that compared with IASC with heat pipe, the collection efficiency of NDASC with heat pipe is improved by 20.4%.Lastly, a solar heat pump system based on NDASC was proposed, which use the NDASC with U-shaped tube as the evaporator. The dynamic model of the system was developed to investigate the changing rule of the parameters in the process of cyclic heating water, which was compared with the solar heat pump system based on IASC. Results show that compared with the solar heat pump system based on IASC, the average coefficient of performance of solar heat pump system based on NDASC is improved by 18.3%.