Photothermal Conversion And Thermal Energy Storage Of Porous Copper-based Composite Phase Change Materials

The energy crisis has become an important problem for mankind,and the use of non-polluting primary energy sources such as solar energy has become a development trend.The solar radiation energy density of sunlight reaching the surface of the earth is low,which is subject to changes in natural conditions such as seasons,climate,time and latitude,and has the shortcomings of thinness,discontinuity,and instability.It is difficult to be used by existing storage materials and devices.Direct absorption and utilization,so additional light trapping and light-to-heat conversion materials or devices are required.In recent years,people have become more and more interested in the use of phase change materials(PCM)for thermal energy storage systems,which can provide high storage capacity and isothermal behavior.The wide application of composite phase change materials is limited by relatively low thermal conductivity.In order to overcome this limitation,the porous feature and good skeleton connection of the foamed metal can realize the embedding of the phase change material,which is an effective means to improve the equivalent thermal conductivity of the phase change material and improve the performance of the phase change material.In this project,porous copper-based photothermal conversion materials and composite phase change materials based on porous copper foam were prepared,and their thermal conductivity,stability,photothermal conversion,and thermal energy storage properties were studied.This paper is mainly divided into three parts:Part Ⅰ: The photothermal conversion efficiency of the collector is enhanced by adjusting the structure and band gap of the semiconductor material.The mesoporous Cu O prepared by a simple method has a narrower band gap than commercial copper oxide,and the mesoporous Cu O has better optical absorption performance and dispersion stability.Mesoporous Cu O nanofluids with different light intensity and different concentrations have higher temperature rise than commercial Cu O nanofluids.The photothermal conversion efficiency of 50 ppm mesoporous Cu O/water nanofluid and commercial Cu O/water nanofluid are 83.66% and58.86%,respectively.Mesoporous Cu O brings new paradigm for mesoporous metal oxides as the working medium for direct absorption of solar collectors.Part Ⅱ: The copper foam-based composite phase change material is composed of copper foam as the carrier,graphene oxide and reduced graphene oxide as surface modifiers,and paraffin wax and polyethylene glycol 10000 as the organic phase change material.The copper foam modified by the surface modifier provides a large number of active sites for the adsorption of the phase change material,and the composite phase change material has a stable shape and is not easy to leak.When the solar radiation intensity is 1000 W?m-2,the surface temperature of the composite phase change material rapidly rises to 70°C within 200 s.Compared with pure phase change materials,the thermal conductivity of copper foam/reduced graphene oxide/paraffin is increased by 300%,the latent heat enthalpy is111.53J/g,and the photothermal conversion efficiency is as high as 86.68%.Our approach not only provides a new way for facile manufacturing of high-performance composite phase change materials,but also integrates the processes of solar energy utilization.The composite phase change materials exhibit good optical absorption performance,fast thermal response and excellent thermal storage capacity.Part Ⅲ: Metal-organic frameworks(MOFs)have the advantages of rich pore structure and high specific surface area.The combination of MOFs and carrier materials can improve the functionality and interface compatibility of the carrier.The copper foam-based MOF material is obtained by the in-situ growth method,and the MOF particles provide a controllable morphology structure for the adsorption of the phase change material.The MOF-based composite phase change material improves the thermal conductivity of the pure phase change material,reduces the leakage of the phase change material,strengthens the optical absorption of the composite material,and improves the thermal energy storage efficiency and total thermal energy of the composite material.Realize the integrated design idea of "solar energy collection,photothermal conversion,thermal energy transportation and storage" of porous copper-based composite phase change material.