【作者】 李伟；

【导师】 刘向农； 仰叶；

【作者基本信息】 合肥工业大学 ， 动力工程（专业学位）， 2021， 硕士

【摘要】 定形复合相变材料具有相变潜热值大,导热系数较高,塑形简单等特性,使得相变蓄热技术有着很高的工业价值,适用于动力电池控温、电子器件热管理、电动汽车除霜等领域,所以对相变蓄热系统的优化研究有重要意义。多数文献是从相变材料性能、换热器优化角度展开研究,缺少对于释热方式的探究,因此,本文通过传热流体间歇取热的方式,研究相变蓄热系统周期性释热对于其性能的影响,并对释热工况进行寻优。先使用赤藻糖醇/膨胀石墨复合相变材料制备圆柱形相变蓄热单元,并对相变蓄热单元的相关热物理性质进行测量。结果表明:它的平均相变温度为117.39℃,相变潜热值为308.7k J/kg,平均导热系数是4.5W/（m·K）,相变过程稳定,未发生衰减现象。在此基础上,搭建以水为传热流体的相变蓄热实验台,采用响应面法中的单因子模块设计实验方案,对相变蓄热单元进行周期性释热实验,并建立以蓄热材料总释热功率、斯蒂芬数以及?效率为指标的评价体系。研究发现:传热流体流速及进口温度不变,当间歇时间为20min,蓄热单元累计释热时间为40min时,评价指标都随运行时间的增加,出现先增加后降低的趋势。其中,（?）效率极值出现的时间要比另外两个指标滞后约22%。综合考量,得出运行时间为7.7min是最佳的结果。进而,构建蓄热单元数值模型,先通过模拟研究相变蓄热单元在系统间歇时的内部热量自均衡现象,发现热量自均衡可以有效提高蓄热单元的释热性能,间歇时间7min是最优选的结果。然后使用响应面法中的BBD模块设计模拟方案,探究运行时间、传热进口温度与流速对蓄热单元释热性能的作用规律,发现t_o=15min,T_in=36.60℃,v=0.3m/s是使得评价指标最优的组合,而且流体流速对于释热性能的灵敏度最高。最后以原模型为基础,在同一质量的前提下,给定目标释热功率,对相变蓄热单元的定性尺寸与释热功率的匹配开展研究,发现定性尺寸每减少0.01m,蓄热单元释热性能平均提高约18%。本文的研究结果有利于进一步优化相变蓄热系统释热运行模式,同时提供的研究模式也为相变蓄热器性能优化提供新的思路。更多还原

【Abstract】 Shaping composite phase change materials have the characteristics of large latent heat value of phase change,high thermal conductivity,simple molding,etc.,which make the phase change heat storage technology has high industrial value.It is applicable to power battery temperature control,electronic device thermal management,electric vehicle defrosting and other fields,so it is of great significance to the optimization of phase change heat storage system.Most of the studies are carried out from the perspective of the properties of phase change materials and the optimization of heat exchangers,and lack of the exploration of heat release mode.Therefore,this paper studies the influence of periodic heat release on the performance of phase change heat storage system through the intermittent heat extraction method of heat transfer fluid,and optimates the heat release conditions.Firstly,a cylindrical phase change heat storage unit is prepared using erythritol/expanded graphite composite phase change material,and the relative thermal physical properties of the phase change heat storage unit are measured.The results show that its average phase transition temperature is 117.39℃,the phase transition latent heat value is 308.7k J/kg,and the average thermal conductivity is 4.5W/(m·K).The phase transition process is stable without attenuation.On this basis,a phase-change heat storage experiment platform with water as the heat transfer fluid was built,and the single-factor module in the response surface method was used to design the experimental plan,and the phase-change heat storage unit was subjected to periodic heat release experiments.An evaluation system based on the total heat release power,Stephen number,and exergy efficiency of thermal materials.The study found that: the flow rate of the heat transfer fluid and the inlet temperature remain unchanged.When the intermittent time is 20 minutes and the accumulative heat release time of the heat storage unit is 40 minutes,the evaluation indicators all increase with the increase of the operating time,and there is a trend of first increasing and then decreasing.Among them,the emergence of extremum efficiency is about 22% behind the other two indicators.Based on comprehensive considerations,a running time of 7.7min is the best result.Then build a numerical simulation model of the heat storage unit,and firstly study the internal heat self-balance phenomenon of the phase-change heat storage unit during the intermittent system of the phase change heat storage unit.It is found that the heat self-balance can effectively improve the heat release performance of the heat storage unit.The intermittent time of 7min is the most preferable the result of.Then use the BBD module in the response surface method to design a simulation program to explore the effect of running time,heat transfer inlet temperature and flow rate on the heat release performance of the heat storage unit,and find that to=15min,Tin=36.596℃,v=0.3m/s It is the combination that makes the evaluation index the best,and the fluid flow rate has the highest sensitivity to the heat release performance.Finally,based on the original model,under the premise of the same quality,the target heat release power is given,and the matching of the qualitative size of the phase change heat storage unit with the heat release power is studied.It is found that every time the qualitative size is reduced by 0.01 m,the heat storage unit The heat release performance is improved by about 18% on average.The research results of this paper are beneficial to further optimize the heat release operation mode of the phase change heat storage system,and the research mode provided also provides new ideas for the optimization of the performance of the phase change heat storage system.更多还原