| Photovoltaic power generation is an important technical support to achieve the goal of carbon peaking and carbon neutralization.Photoelectric conversion efficiency is an important indicator of photovoltaic power generation system.The heat dissipation performance of the panel directly affects the photoelectric conversion efficiency.Strengthening the heat transfer of photovoltaic adhesive film can effectively improve the efficiency of photovoltaic power generation system.Therefore,it is of great significance to study the thermal conductivity of photovoltaic adhesive film.In the experiment,polyvinyl butyral is used as the matrix,boron nitride and carbon nanotubes as the filler,and keep the total mass fraction of the two fillers at 1%.Seven groups of samples are prepared by the solution blending method with the proportions of carbon nanotubes and boron nitride of 0:10,1:9,3:7,5:5,7:3,9:1 respectively,and only containing polyvinyl butyral matrix,The effective thermal diffusivity of each group of samples within the temperature range of 10-292 K is measured by using the transient electrothermal technology and Janis CCS 450 low-temperature system,and the thermal diffusivity,volume specific heat,thermal conductivity and thermal reffusivity of each group of samples are calculated according to the theoretical basis.Firstly,the influence of temperature on the thermal conductivity of the sample is studied.when the ratio of carbon nanotubes to boron nitride is the same,the thermal diffusivity of each group of samples decreases gradually with the increase of temperature,and the thermal conductivity of composite material samples decreases first and then increases.According to the fitting function of phonon thermal reffusivity and temperature,the Debye temperature of each group of samples is greater than 292 K.The number of short wave phonons involved in the collision decreases rapidly with the decrease of temperature,and the process of phonon collision causes the change of thermal conductivity.The variation of thermal conductivity and thermal diffusivity with temperature is related to the crystallinity of the samples,the crystallinity of each group of samples prepared in the experiment is relatively low,and the glass transition temperature is greater than 292 K,and the performance of thermal conductivity changing with temperature is closer to that of amorphous polymer.When the proportion of boron nitride and carbon nanotubes is the same,the thermal conductivity should have increased with temperature rise within the temperature range of 10-292 K,but in the experimental results,In the range of 10-30 K,the thermal conductivity of the composite sample does not increase but decreases.Boron nitride and carbon nanotubes form new thermal conductivity units and aggregates in the matrix.The diffraction effect makes the material with different atomic mass from the matrix no longer an effective scatterer.The impact of phonon collisions will be rapidly weakened,and the scattering has a greater impact on the average free path,resulting in a situation where the thermal conductivity decreases with the increase of temperature in the range of 10-30 K.Secondly,the effects of heating temperature and heating time on the thermal conductivity of composite samples are tested.Sample 3 is heated at 90℃,110℃,135℃and 140℃for 1h respectively and then cool it.With the increase of heating temperature,the thermal conductivity first decreases,then increases and then decreases slightly at 292K;When sample 3 is heated at 135℃for 1h,2h and 4h and then cool it,its thermal conductivity first increases and then decreases at 292 K;The artificial accelerated UV irradiation experiment is carried out on sample 3.Under the same conditions of other factors,the UV irradiation is carried out for 10 days,15 days,20 days and 25 days.The thermal conductivity decreases with the increase of irradiation time at 292 K.Finally,the thermal conductivity of the sample is analyzed according to the filler proportion.At the same temperature point in the range of 10-292 K,with the increase of the mass fraction of boron nitride,the thermal conductivity first increases and then decreases.When the ratio of boron nitride to carbon nanotubes is 5:5,the thermal conductivity reaches the maximum of 0.79 W·m-1·K-1.The experimental results are analyzed from the perspective of synergism and interfacial thermal resistance,and the synergetic efficiency of composite samples is calculated;From the perspective of thermal conductivity model,verify the authenticity of the thermal conductivity of the sample is obtained from the experiment.The number of fillers in sample 6 is different from that in other composite materials.Therefore,Maxwell model,Hamilton Crosser model and Halpin Tsai empirical formula are used to calculate the theoretical thermal conductivity of sample 6;The bridge lapping model and the series parallel thermal resistance model are constructed.The theoretical thermal conductivity of sample 1,sample 2,sample 3,sample 4 and sample 5 are obtained according to the Maxwell Garnett equivalent medium theory.It is found that the trend of the thermal conductivity obtained from the experiment is roughly consistent with the theoretical thermal conductivity;The heat conduction network is constructed by boron nitride and carbon nanotubes in polyvinyl butyral matrix.When the proportion of boron nitride and carbon nanotubes is 5:5,the heat conduction performance of polyvinyl butyral matrix is most significantly enhanced;When the content of boron nitride filler is small,the effective thermal conductivity path constructed by carbon nanotubes and boron nitride is less,and even agglomeration phenomenon occurs,resulting in relatively low thermal conductivity. |
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