Experimental And Numerical Investigation Of A New Light-to-thermal Energy Storage Phase Change Material

For a long time,solar energy has become one of the research hotspots in the field of energy due to its advantages of wide source,clean and pollution-free and renewable.However,due to the shortcomings of solar energy instability and intermittency,it leads to the problem of mismatch between energy supply and demand,which limits its wide application.Latent heat storage technology has been applied to solar thermal storage systems due to its advantages such as high energy storage density and constant flushing temperature.The traditional phase change material（PCM）has problems such as low thermal conductivity,easy leakage,and poor absorptance,which limits the widespread application and commercialization of solar thermal storage systems.In this paper,graphene aerogels（GA）doped with carbon nanotubes（CNTs）have a highly thermally conductive network structure,and encapsulating traditional organic PCM with it solves the defects of traditional PCM.The main research work of this article is as follows:In this study,a composite phase change material（PW/GA/CNTs）composed of graphene oxide（GO）and carbon nanotubes（CNTs）mixed graphene aerogel as the porous skeleton support structure and paraffin（PW）as the phase change matrix.In the PW/GA/CNTs,PW is encapsulated with graphene aerogel with a porous network structure,which plays a role in anti-leakage and shape-stable during the phase transition process,while providing more efficient heat conduction channels.CNTs wrapped around the skeleton structure and filled in the porous medium can increase the thermal conductivity surface area,which can further improve the thermal conductivity.The thermal conductivity of the PW/G2C1-CA sample with 2.2 wt%hybrid graphene aerogel is as high as 0.46 W m^-1 K^-1,which is 1.77 times that of pure PW(0.26W m^-1 K^-1);The average absorptance in the wavelength range of 0.3-2.5μm is close to 1,which is 1.4 times that of pure PW;it has a latent heat value close to that of pure PW.The numerical model of phase change heat transfer in porous media is established.By comparing with the experimental results,the numerical model has good accuracy.On this basis,a numerical model based on solar unglazed flat plate collector was established to simulate the coupling process of light-to-thermal conversion,thermal energy storage and thermal energy application of composite PCM in solar thermal storage system.Compared with PW type heat collector,the overall temperature distribution of PW/G2C1-CA type collector is more uniform during the light-to-thermal conversion process,and the average body temperature at the end of the light-to-thermal conversion is 20°C higher than that of PW type phase change collector.PW/G2C1-CA type collector has a total efficiency of 27%,which is 13%higher than that of the PW type collector.Convective heat transfer loss and radiant heat transfer loss account for32%and 41%.It can be seen that PW/G2C1-CA type collector shows good heat storage and release performance in solar energy storage systems,and have certain engineering application potential.Taking the phase change collector in the discharging process as the research background,a 2D phase change unit was established.The BOBYQA algorithm and the phase change heat transfer model were combined to improve the layout of the traditional Y-shaped fins.The minimum objective function and constraints were established.The target parameters are optimized to explore the fin layout with the shortest discharing time.The results show that the optimized structure shortens the heat release time by 74%.