| With the development of the national economy,the demand of high quality energy and power supply is constantly increasing.It is an effective method to store energy during the valley period,and release heat at the peak of electricity consumption by phase-change materials,with the great significance for power system safety and stability in operation.At the same time,with the support of electric market,phase-change heat storage has been the most promising research topic in practical industrial and civil heating applications.At present,scholars at home and abroad research on phase change heat storage mainly aim at a material or a single structure to build a test bench for measurement or simulation analysis.It also found that not enough has been done on the system efficiency,operation and maintenance,service life from the thermal user demand or system level to study the economic efficiency,operational performance and feasibility of actually applying on the valley heat storage.In view of the insufficiency of current research,the research goal of this project is to construct a phase change thermal storage system suitable for building heating,which not only analyzes the performance of the phase change thermal storage device,but also addresses the thermal requirements,system efficiency,and operating costs,based on the economical and feasibility analysis.According to research objectives and ideas of the project,the main research contents of this paper are as follows:Firstly,the phase change thermal storage unit is designed according to the thermal load demand.Based on the theory of phase change heat transfer,the physical model of the phase change thermal storage unit is established,and the phase change thermal storage system is set up as an experimental platform to measure the preliminary design of the thermal storage unit.The experimental results of the heat storage,heat storage,and heat release processes show that the phase change unit can complete heat storage in 2 hours,with a heat storage capacity of 7300KJ,an average heat loss of 15 W,and a heat storage efficiency of about 91.3%.During the exothermic process,as the flow rate increases,the effective heat release power gradually increases during the effective heat release time,but the effective heat release performance gradually decreases.Combined with the effective heat release time and flow rate,the preferred heat release condition is that the flow direction is from bottom to top is 9.5L/h and the flow rate is 9.5L/h,and the effective energy release efficiency of the system is about 52.2%.Due to the low system efficiency under the initially designed structure,there is still a large latent heat and internal energy in the unit body after the completion of the heat release.In order to further improve the system performance,the internal level of the phase change unit is added.The fins were optimized for structural design and the best structural parameters were obtained by numerical calculations on a computer platform.The results of CFD calculation showed that the optimization of the heat release process was the best when the number of fins was 8 and the length was 6 cm.At this time,the heat transfer coefficient is about 470 W/(m~2.K).Compared with the structure without fins,the effective heat exchange time increases to about 75 minutes,the instantaneous heat release power change is relatively slow and the total system can be increased to 79%.Based on the actual user heat load change situation and the operation law of the phase change heat storage subsystem,the entire valley power utilization heating system is designed based on the optimized phase change unit body structure and operating conditions,and according to the needs of heat users,the economic benefits of the change analysis system indicate that the project has a short payback period and small investment risk when the peak-to-valley electrical difference is greater than 0.6 yuan/degree and a small investment risk;after the end of the system operating cycle,only when the heat users average the annual When the heat is 50%of the design value,or when the peak-to-valley difference is less than 0.32yuan/degree,the NPV value is less than 0 million yuan and the investment cost cannot be recovered.The NPV value under all operating conditions is greater than 0,and peak-to-valley The larger the difference and the higher the heat extraction rate,the higher the total return of the system.Therefore,the design system has higher investment potential and recycling profit in large-scale industrial or residential heating operations.The research of this subject provides the relevant theoretical basis and experimental support for the development and application of phase-change heating system on valley electricity utilization,and provides reference ideas for the research of phase-change heat storage and heating.The experimental and simulation results show that the built-in phase-change thermal storage system used in this paper has higher economic value and application prospects in large-scale civil and industrial scenarios,and it plays a good role in achieving stable and efficient operation of the grid during peak load shifting and valley filling. |
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