Preparation Of Composite Phase Change Energy Storage Materials And Its Application In Photothermal System

In recent years,with the increasing level of greenhouse gas emissions and the rapid consumption of fossil fuels,the problems of environmental pollution and energy shortage have become increasingly serious.So renewable energy has received increasing attention.As one of the most important clean energy,solar energy has the advantages of low cost and wide sources.Phase change materials(PCMs)can change the state of matter and provide latent heat under a constant temperature.PCM plays an important role in solar thermal conversion and energy storage,which have received more and more attention in recent years.Doping with high doses of conductive particles can effectively improve the thermal conductivity of PCM.However,the particles will accumulate on the surface to reduce light absorption and reduce the overall energy storage density of PCM.In this study,by integrating the low-temperature phase change material DMannitol(DM)and acetylene black nanoparticles with high conductivity,a volumetric absorption solar absorber was designed,which was equipped with low concentration(0.05 wt%)of acetylene black nanoparticles.This doping can maintain a high phase change enthalpy(295.2 k J/kg)of DM,and can effectively improve the thermal conductivity of PCM.5.0 wt% acetylene black nanoparticles make the thermal conductivity increase by 26.4%,from 0.68 W·m-1·K-1 of pure DM increased to 0.85 W·m-1·K-1.Acetylene black nanoparticles also promote DM nucleation,reduce supercooling,and improve thermal management performance.The performance of PCM with different doping concentrations of acetylene black nanoparticles was compared through various characterization methods.The composite PCM with the most suitable doping concentration(0.05 wt%)was selected and compared in actual work with a commercial typical surface absorber.In the photothermal conversion test,the addition of acetylene black nanoparticles can effectively improve the full spectrum absorption of PCM and increase the 41.86% light absorption rate of pure DM materials to more than 90%.Compared with the traditional surface absorption-type PCM,the volumetric absorption-type PCM significantly reduces the temperature difference inside the material.At the same thickness of 10 mm,the working mode of volumetric absorption reduces the temperature difference between the upper and lower surfaces from the surface absorption type of 103.1°C to 62.7°C.For the first time,the solar thermoelectric generator(STEG)system was studied for the solar thermal conversion and energy charging and discharging performance of PCM.The results show that the volumetric absorber can reach 198.2°C at the bottom of the PCM,and the corresponding open circuit voltage is 0.65 V.These performance data are significantly better than surface absorber.The corresponding results in the surface absorption mode can only reach 135.1? and 0.45 V,indicating that the volumetric absorption mode can significantly improve the performance of PCM.This new low-cost,easy-to-prepare volumetric PCM provides a very promising idea for further improvement.