The Experimental Research On EG/Paraffin Composite Thermal Storage Heating Device By Utilizing Off-peak Power

Under the policy background of coal to electricity and the macroscopic demand for energy storage technology by peak load shifting in power grid,developing thermal storage heating by valley-electricity is of great significance for promoting the consumption of valley electricity and achieving clean heating.However,at present,there is a lack of a decentralized heat storage electric heating device with a simple and practical structure and good economic efficiency,and the traditional valley electricity heat storage heating device needs to occupy a certain use space inside the building.Based on this,a modular valley electricity utilization phase change heat storage wall suitable for prefabricated buildings was proposed in this paper,its basic components heat storage performance was also analyzed combining with experiments and numerical simulations.The operating parameters and heat exchange structure were optimized to improve the overall efficiency of the system where electrical energy is converted into effective heat.The specific research contents are as follows:Based on the temperature,safety and stability requirements for building heating,paraffin with a phase transition temperature of 62 °C was selected as the matrix heat storage material,and EG was selected as the reinforced thermal conductive material through dynamic thermal response experiments.Then EG/paraffin composite PCM with different mass fractions were prepared,through a series of characterization of thermal properties,it was found that the thermal conductivity and porosity of composite PCM increased with the increase of EG content,the thermal conductivity of 12wt% composite PCM was 12 times higher than that of pure paraffin,and the latent heat will decrease with the increase of EG ratio,but the phase transition temperature is basically not affected.In terms of designing the material packaging container,firstly,the concept of phase change heat storage unit was put forward in combination with the idea of modularization.Then,the basic parameters of the heat storage unit were designed according to the heat storage scene and heat exchange structure requirements.Finally,the actual performance of heat storage and release was explored through experiments.The results show that the surface heating source provided in the heat storage unit effectively prevents local overheating during the heat storage process.After applying the composite PCM,the heat storage time of the phase change heat storage unit was shortened by 23%,and the heat storage efficiency was increased from 93% of pure paraffin to 97%.The average heat dissipation power during the heat dissipation process was increased from 14.3W to 22.5W in the paraffin phase change unit,but under the limitation of the minimum heat dissipation power,the effective heat dissipation efficiency of the heat storage unit under a single operating condition was only 63.4%.With the help of numerical simulation platform,the heat release process of the constructed single-tube heat storage body was optimized and simulated.The results show that: under the optimal operating parameter combination,the effective heat release efficiency is 88.28%;it is found that the heat storage body with the highest aspect ratio has the highest effective heat release efficiency by size optimization,but the heat storage density is reduced by about 19.1%;the performance of the three heat exchange tube structure heat storage bodies has been greatly improved compared with the original heat storage body,especially the inner finned tube heat storage body,and the instantaneous heat dissipation power in the early stage is improved compared with the smooth tube nearly 80%,the effective heat release efficiency is as high as89.48%Valley electricity heat storage wall module is designed,polyurethane material is selected as inner insulation layer and foamed ceramic is used as outer frame,the engineering assembly plan of valley electricity storage wall is given,then the application economy of electricity heat storage wall system was analyzed,the result shows: due to the large initial investment,the net present value of the project within a 20-year operating period is only 139,100,and the rate of return is low.Subsequent research needs to further optimize the overall structure,reduce material costs,and increase the overall thermal efficiency of the system.