| With the rapid development of society and economy, the demand for energy is increasing. But the continuous depletion of fossil energy and living environment is deteriorating, which gradually become the two major problems restricting the progress of human civilization. Developing and utilizing solar energy and other clean energy sources and improving energy efficiency are the inevitable way to solve the above problems. The energy storage technology is an important means of using clean energy, collecting industrial waste heat and electrical network peak shaving. Phase change energy storage is an important manifestation of latent heat storage in the storage technology. In this paper, the phase change material and the multi-tube phase change thermal accumulator are studied deeply.For the traditional phase change occurs in the liquid phase leak when phase of materials is changing and low thermal conductivity, the PEG/SiO2/EG composite shape-stabilized phase change material was prepared though sol-gel method and vacuum leaching infiltration method in this paper. It not only solves the defects of the liquid leak when the material is in phase transition, but also greatly improves the thermal conductivity of the material, which increases the thermal conductivity from 0.256 W/(m · k) to 1.862W/(m · k). And the latent heat value of PEG/SiO2/EG is 129J/g. This kind of material is used as the multi-tube phase change thermal storage medium. Meanwhile, a heat storage unit was selected as the research object in this paper. The heat transfer models of the organic phase change materials and the shape-stabilized phase change materials were established respectively. The heat transfer models were validated by building the phase change thermal accumulator experiment table and other experimental data of others. The heat transfer influence factors of thermal accumulator were calculated and analyzed by using the heat transfer models and FLUENT software. The results as follows:1. with the pipe number increases, the heat storage rate gradually increased, but the increased range became smaller and smaller which result in strengthen heat transfer effect is limited; 2. the material of the heat exchange tube has little influence on the heat storage effect, so the economic factors should be mainly considered when selecting the heat exchange tube; 3. too small heat exchange tube spacing causes serious "thermal short circuit" phenomenon, but too large tube spacing increases the thermal resistance of phase change materials. Thus the heat exchange tubes are appropriately arranged according to the actual situation; 4. when the number of pipe roots is more, the heat storage rate of heat medium cross flowing was better than that of the same direction which contained the temperature drop in the tube to a certain extent; 5. increasing the inlet velocity can shorten the heat storage time, but the effect is not obvious. Increasing the flow rate of the tube caused by the increase of the pump power consumption is not desirable. And the influence of inlet velocity of heat medium on the heat storage rate and heat release rate is great. Therefore, it should try to expand temperature difference of heat exchange tube and phase change materials in the use of the accumulator.Finally, a variety of enhanced heat transfer methods were compared in this paper, which included the traditional adding fins, adding the expansion graphite with high thermal conductivity and the multi-tube type. When the geometric model was the single-tube heat storage unit, the heat storage time of working condition which added the expanded graphite was reduced by 25.52% than that in the condition of adding fins. When heat storage medium of thermal accumulator was PEG/SiO2/EG, the heat storage time of working condition which used multi-tube type was reduced by 25.52%, than that in the condition of adding fins.In summary, the combination of the phase change material and the multi-tube thermal accumulator can improve the heat storage rate, which has a good application prospects. |
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