Study On Photothermal Properties Of Paraffin Containing Composite Nanoparticles

Phase change materials(PCMs)are widely used to store solar energy due to their excellent latent heat storage properties.As a typical phase change material,paraffin has noncorrosivity,phaseless separation,high latent heat and stable physical and chemical properties,which is often used in many fields such as building energy conservation,battery thermal management,solar thermal utilization.However,the poor thermal conductivity and spectral absorption of paraffin limit its application range and affect its application value.Adding nanoparticles can effectively improve the photothermal properties of paraffin.Since liquid paraffin is an oil-based liquid with stable physical and chemical properties,the stability of nanoparticles in it is lower than that of distilled water and inorganic phase change materials.Therefore,the preparation of uniform and stable paraffin containing nanoparticles and the regulation of the photothermal properties of paraffin by controlling the parameters of nanoparticles are of great significance to expand the application range of paraffin and improve the practical value.Combined with the improvement of the photothermal performance of paraffin by various nanoparticles,two-component composite nanoparticles were selected to optimize the photothermal performance of paraffin.Due to the non-polarity of paraffin,the electrostatic repulsion between nanoparticles cannot be formed,resulting in poor stability.Therefore,the stability of paraffin-based nanoparticles enhanced phase change material(NePCM)was improved by reducing the concentration,adding dispersants and suitable ultrasonic treatment time in the preparation of NePCM.In order to explore the effect of composite nanoparticles on the thermal performance of NePCM,the thermal storage performance and heat transfer performance of paraffin containing composite nanoparticles were analyzed by experimental measurement method.The results showed that the composite nanoparticles had obvious enhancement effect on thermal properties of NePCM,and the improvement effect of Zn-Ti N composite nanoparticles was significantly better than that of Zn-ZnO composite nanoparticles.Compared with pure paraffin,the latent heat of phase transition of Zn-Ti N NePCM and Zn-ZnO NePCM can be increased by 40.69 % and 34.14 % under the influence of the sensible heat of nanoparticles,respectively.The thermal conductivity of NePCM increases with the increase of nanoparticle concentration.At the same concentration,the higher the temperature,the greater the thermal conductivity.However,at the same concentration,the thermal performance of NePCM has no obvious regularity in a certain range with the change of the mixing ratio of composite particles.It is worth noting that Zn-Ti N nanoparticles with volume fraction of 0.001 % have a certain negative impact on the thermal storage performance of NePCM.In order to explore the influence of composite nanoparticles on the optical properties of NePCM,a transmittance measurement device based on jet liquid film independent of optical window and container was built to measure the spectral absorption characteristics of paraffin containing composite nanoparticles.The results show that the composite nanoparticles can effectively improve the spectral absorption of NePCM.Without considering the scattering effect of nanoparticles,the solar weighted absorption fraction of NePCM increases with the increase of nanoparticle concentration,namely,under the same conditions,the spectral absorption performance of NePCM increases with the increase of nanoparticle volume fraction.Among them,Zn-Ti N composite nanoparticles have a better improvement on the spectral absorption performance of NePCM,which can be increased by 60 % at a low concentration.Zn-ZnO composite nanoparticles can improve the light absorption of NePCM and ensure the transmittance in the visible range.In order to explore the effect of composite nanoparticles on the photothermal conversion performance of NePCM,the solar photothermal conversion efficiency of paraffin containing composite nanoparticles was studied by experimental method.The results showed that the stability of high-concentration paraffin-based NePCM was poor.Although the spectral absorption performance of NePCM increased with the increase of the volume fraction of nanoparticles,the photothermal conversion efficiency of highconcentration NePCM decreased.Photothermal conversion efficiency of pure paraffin is only 22.69 %,Zn-Ti N NePCM is 42.60 %,Zn-ZnO NePCM is 40.59 %;most NePCMs cannot convert all the absorbed light energy into heat energy,but Zn-Ti N NePCM and Zn-ZnO NePCM with particle mixing ratio of 8 : 2 have better photothermal conversion effect.In order to explore the energy-saving effect of paraffin containing composite nanoparticles in the application of building glass envelope,a numerical model was established based on the photothermal transmission mechanism of glass windows.ZnZnO NePCM with volume fraction of 0.001 % and particle mixing ratio of 8 : 2 was used as the filling material of the middle layer of double-layer glass to numerically simulate the photothermal performance and energy consumption of NePCM glass windows in severe cold regions.The results show that compared with the pure paraffin window,the Zn-ZnO NePCM window can meet the indoor lighting and temperature suitability,and reduce the annual total energy consumption of the building envelope by 2.78 %.