【作者】 刘霞；

【导师】 饶中浩；

【作者基本信息】 中国矿业大学 ， 制冷与低温工程， 2018， 硕士

【摘要】 相变储能利用相变材料的潜热吸收和释放热量,被广泛应用于制冷、太阳能热存储和余热回收等领域。相对于单级相变储能,多级相变储能可保持热流体和相变材料之间的温差,具有更高的储能速率。本文设计了两级相变储能系统,并通过模拟和实验的方法研究了雷诺数、瑞利数和进口温度等对储能速率的影响规律。本文主要结论如下:(1)建立了含径向翅片的两级相变储能系统数值模型。为提高储能效率,在径向翅片上设置了轴向翅片,并分析了含轴向翅片和不含轴向翅片储能系统的储能速率。结果表明,添加轴向翅片可削弱翅片处的热量积聚,强化了两级相变材料间的热量传递,使温度分布更均匀。在添加了轴向翅片后,储能系统内两种相变材料的完全熔化时间相对缩短了21.79%和13.87%。(2)为探明含轴向翅片的两级相变储能系统储能的传热特性,对系统进行了无量纲分析,研究了雷诺数、瑞利数和材料物性等参数对储能速率的影响规律。结果表明,增加系统雷诺数或瑞利数可提高系统储能效率。但是,雷诺数或瑞利数对储能系统的影响随着雷诺数或瑞利数的增加而减小。当瑞利数从0.8×10~5增大到1.2×10~5时,系统的总储能量增加了0.091。当瑞利数从2.0×10~5增加到2.4×10~5时,系统的总储能量仅增加了0.029。(3)为提高相变材料的传热性能,将膨胀石墨和石蜡复合制备了复合相变材料。将复合相变材料作为储能材料,并搭建了两级复合相变储能实验平台,研究了雷诺数及热流体进口温度对储能系统储能速率的影响规律。结果表明,复合材料两级相变储能系统的储能量随着热流体雷诺数的增大而增大。当雷诺数从66.8提高到140.1后,储能量增加了0.28×10~4 J。当雷诺数从250.4提高到375.6后,储能量提高了0.02×10~4 J。此外,增加热流体的进口温度可提高储能系统的效率。在18000 s时,热流体进口温度为353.15K储能系统的储能量比进口温度为323.15K系统的储能量提高了1.8倍。本文结论对于提高两级相变储能系统储能效率、推广相变储能在制冷、太阳能存储等领域的应用具有指导意义。更多还原

【Abstract】 The phase change energy storage(PCES)utilizing the latent heat of phase change material(PCM)to absorb and release heat,has been widely applied to refrigeration,solar energy storage and waste heat recovery.Compared with the single-stage PCES,the multi-stage PCES can keep the temperautre difference between PCM and thermal fluid,leading to more effective energy storage rate.In this dissertation,the two-stage PCES has been established and the effects of Reynolds number,Rayleigh number and inlet temperature on energy storage rate are investigaed by numerical and experimental methods.The major conclusions are as follows:(1)In this dissertation,the numerical model of two-stage PCES has been established.In order to improve the energy storage rate,the axial fin is set.The comparisions of energy storage rate are conducted.The results show that,the heat accumulation near the fin can be weakened by axial fin and the heat transfer between two PCMs can be enhanced.Besides,with the axial fin,the temperature distributes more uniformly,and the total melting times fo the two PCMs has been reduced by 21.79%and 13.87%.(2)In order to find out the heat transfer performance of two-stage PCES with axial fin,the dimensional analysis has been conducted and the effects of Reynolds number,Rayleigh number and thermal properties of PCM on energy storage rate have been investigated.The results show that,the impacts of Reynolds number or Rayleigh number are reduced with the increase of Reynolds number or Rayleigh number.When the Rayleigh number is increased from 0.8×10~5 to 1.2×10~5,the total stored energy is increased by 0.091.When the Rayleigh number is raised from 2.0×10~5 to 2.4×10~5,the total stored energy is only increased by 0.029.(3)In order to enhance the heat transfer performance of PCM,the coupled PCM is formed from expanded graphite and paraffin.The coupled PCM is utilized in two-stage PCES,and the corresponding experimental platform is establihsed.The influnces of Reynolds number and thermal fluid’s inlet temperature are studied.The results show that,the stored energy is increased with the Reynolds number.When the Reynolds number is increased form 66.8 to 140.1,the stored energy is increased by 0.28×10~4 J.When the Reynolds number is increased from 250.4 to 375.6,the stored enery is raised by only 0.02×10~4 J.Besides,increasing the inlet temperature can enhance the efficiency of energy storage,and increase the stored energy.When the time is 18000 s,the stored energy of the system with inlet temperature of 353.15 K is 1.8 times more than that of323.15 K.The resutls of this dissertation are able to help to improve efficiency of the two-stage phase PCES,and extend the application of PCES in refrigeration,energy storage of solar energy.更多还原