| Under the global energy crisis and strict requirements of carbon emissions,solar energy and industrial waste heat have great potential for development.However,these energy systems are usually discontinuous and unstable.The application of thermal energy storage technology can alleviate the imbalance between energy supply and demand and advocate energy utilization.The study of recycled thermal storage materials from solid waste resources can further enhance the economic and environmental benefits of thermal storage technology.For steel slag and blast furnace slags,the sensible thermal storage materials based on metallurgical slag and modified by carbonate activation.The morphology and phase of the material kept unchanged after 200 cycles,indicating its good thermal stability.The steel slag remains stable until 1200? by TG-DSC test.The thermal energy storage density of steel slag is 797.9kJ·kg-1 from 400 to 900?,the thermal conductivity measured as 0.505,0.532 and 0.670 W·(m·K)-1 at 25,250 and 500? respectively.When the mass ratio of sodium carbonate modified steel slag is 3:5,the morphology of the material remains stable after the thermal cycle test,and the trend of the DSC curves remain the same.The thermal energy storage density of the sodium carbonate modified steel slag is 997 kJ·kg-1 from 400 to 900?,which is 25.32%higher than pure steel slag.Even more,the thermal conductivity is 1.331,1.323,0.889 W·(m·K)-1 at 25,250,and 500?,respectively,which is 32.7%higher than that of steel slag.The thermal performance of sodium carbonate modified steel slag has been significantly improved with developed activation process.Resource recycled form-stable PCMs were developed with modified metallurgical slag as matrix and carbonate as phase change material.The potassium carbonate is uniformly distributed in modified steel slag-based composite potassium carbonate form-stable PCMs,and has good chemical compatibility with modified steel slag.With the increase of potassium carbonate content,the latent heat of the composite PCMs gradually increases,and consist with the theoretical values.By 200 thermal cycles experiment,it is found that the best mass ratio of modified steel slag-based composite potassium carbonate form-stable PCMs is 6:4,the thermal stability is the best,and there is no breaking or leakage,the latent heat value decreases 7.08%,and the mass loss is 6.56%.The chemical compatibility of modified metallurgical slag-based composite sodium carbonate form-stable PCMs are good by XRD test,however the composite materials deformed and leaked easy occurred in the thermal cycle test.Further,binary NaLiCO3 were composite with the modified metallurgical slag-based form-stable PCMs,the chemical compatibility between the modified steel slag and NaLiCO3 are good,and the chemical compatibility between the modified blast furnace slag and NaLiCO3 is poor.With the thermal cycle progresses,the modified blast furnace slag continues to react with NaLiCO3 and form LiCaSiO4.The low thermal conductivity of PCMs is often a prohibit for heat transfer performance.In order to solve this problem,a three-dimensional unsteady simulation was conducted to study the influences of the fin structure,thickness,number,and spiral cycle on the heat storage performance.The mean temperature,liquid fraction,and heat storage of the PCMs during the melting process were also discussed.The simulation results showed that the melting time of the PCMs of the spiral fin heat storage unit is shortened by 12.21%compared with that of the flat fin.With the increase in the thickness,number,and spiral period of spiral fins,the amount of heat storage slightly reduces.However,the PCMs melting time is shorter,and the heat transfer performance is improved continuously. |
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