Experimental Study On The Thermal Performance Of Graphene Nanofluids Heat Pipe Solar Collector

Solar energy is one of clean,highly-efficient resources.The highest degree of commercialization and the most popular promotion is solar thermal utilization in the field of solar utilization.The heat pipe solar collectors as a common form of solar collectors,which uses the gravity heat pipe for solar application as the core component of heat transfer.Due to the large fluctuation of the heat flux and the characteristics of the low heat flux in the solar radiation,it is necessary that the heat pipe must have excellent running start characteristics.In this paper,a kind of graphene nanofluids heat pipe solar collectors was proposed and studied.In order to improve the starting performance and running characteristics of solar gravity heat pipe,water-based graphene nanofluids by adding graphene nanoparticles in deionized water were prepared,which were used as the working fluid of solar gravity heat pipe.Based on the study on the starting characteristics of graphene nanofluids heat pipe,the effect of graphene nanofluids solar gravity heat pipe on the heat pipe solar collector was studied.The main work of this paper includes the following aspects:1)Preparation,Stability and Thermophysical Properties of Nanofluids.Four kinds of water-based graphene nanofluids with different mass concentrations were prepared.The influence of the amount of dispersant on the stability of nanofluids was explored by spectrophotometer.The optimum amount of dispersant added to the preparation of graphene nanofluids was obtained.The thermal conductivity,viscosity and contact angle of the nanofluids were tested and the mechanism of enhancing the thermal conductivity by adding graphene nanoparticles to deionized water was analyzed.Finally,the influence of the thermal conductivity and viscosity on the heat transfer performance of the heat pipe was analyzed by the coupling characteristics of the gravity heat pipe,and the suitable concentration range of the nanofluids was determined theoretically with the dispersion stability of the nanofluids.2)Study on Start up Characteristics of nanofluid Solar Gravity Heat Pipe.The heat pipe isothermal test was carried out to ensure that it was in accordance with the experimental requirements.In the heat pipe isothermal test,the proper charge of the heat pipe was determined.Through the heat pipe wall temperature distribution experiment,reached the "visualization" of solar gravity heat pipe start process.Simulated solar gravity heat pipe for the actual working conditions of solar collectors,different heating power,starting characteristics of solar gravity heat pipe with different heating power,different circulating water temperature and different inclination angle were studied in detail.Finally,the start up characteristics of the nanofluids heat pipe was studied by comparing the heat transfer performance of the heat pipe with different graphene concentration.3)Two different heat pipe forms of vacuum tube solar collector experiment system were designed.The thermal performance of the vacuum tube solar collector system in this new heat pipe form was studied experimentally by using the graphene nanofluid heat pipe in the vacuum tube solar collector,and the deionized water heat pipe vacuum tube collector system as a control.4)Based on the analysis of the rationality of the heat collecting test system of the heat pipe type vacuum glass tube collector,two kinds of heat pipe flat-plate solar collectors with graphene nanofluids heat pipe and deionized water heat pipe were designed respectively.Based on the initial experimental test,the parallel operation experiment of two kinds of collectors was carried out.The heat collecting performance of the two systems was analyzed and compared,and the temperature distribution of the two plates was analyzed.