| With the environmental problems becoming more and more serious,the collection and use of clean energy begin to receive the attention of all countries in the world.In this paper,a method combining experiment with theory is proposed to add nanoparticles into the lower convective zone(LCZ)of a small salt-gradient solar pond to enhance its thermal performance.Firstly,a two-step method was used to prepare LCZ based nanofluids,including carbon nanotube nanofluids with mass fractions of 0.0015%,0.005%,0.01%,0.02% and 0.1%,and Cu O nanofluids with mass fractions of 0.01%,0.02%,0.05%,0.1%and 0.2%.Then the sedimentation experiment and heat collection experiment were carried out.Finally,0.01% carbon nanotubes and 0.1% Cu O nanofluid with the best experimental effect were selected to be added into the LCZ of the solar pond to carry out comparative tests with ordinary salt gradient solar pond.The experiment result shows that:In the solar pond containing carbon nanotubes,the heat of the solar pond is stored in the LCZ,and the highest temperature in the middle of the LCZ reaches 35.35℃.The average temperature of the LCZ increases by 1.7℃,and the efficiency is 1.2 times that of the ordinary salt gradient solar pond.In the solar pond containing Cu O nanoparticles,the maximum temperature is in the lower part of the none-convective zone(NCZ)and reaches37.3℃,which is 3.5℃ higher than that of the common salt gradient solar pond.Compared with the common salt gradient solar pond,the efficiency increases by 25%,and the average temperature of LCZ increases by 2.6 ℃.These results indicate that nanoparticles can effectively improve the heat collection efficiency and heat storage temperature of solar pond,and the effect of Cu O nanoparticles is better than that of carbon nanotubes.Carbon nanotubes have better stability,more uniform temperature distribution in LCZ,and less influence on the NCZ.In addition,since the experiment was conducted in late November and December,the ambient temperature was relatively low,especially when the lowest temperature dropped to about-10℃ at night,which had a certain impact on the overall temperature of the solar pond.Finally,a physical model was established based on the experimental parameters,and the temperature and concentration fields inside the solar pond containing nanoparticles were simulated theoretically,and compared with the experimental results.The results show that the average temperature in the solar pond containing nanoparticles is higher than that in the common salt gradient solar pond,and there is a small convection heat transfer phenomenon on the surface and near the wall of the solar pond.The results are basically consistent with the experimental results. |
