基于水合盐吸附的跨季节储热特性数值研究

发布时间：2018-04-08 21:46

  本文选题：热化学储热　切入点：水合盐　出处：《华北电力大学(北京)》2016年硕士论文

【摘要】：跨季节储热技术中,水合盐热化学吸附具有储热密度高、长周期存储无热损、清洁环保、成本低廉等优势,逐渐成为国内外储热领域的研究热点。本文对基于水合盐热化学吸附的跨季节储热技术的发展进行了深入调研,对比分析不同水合盐储热材料的储热特性和反应器选型的优劣。由于低温运行条件下,储热材料MgCl_2·6H_2O表现出优良的反应性能,结合本文数值模拟的需求,选择以MgCl_2·6H_2O颗粒材料构成的堆积床反应器作为模拟对象。针对MgCl_2·6H_2O堆积床反应器中固体颗粒吸附剂表面发生的热化学储热过程进行理论建模,建立与热化学反应耦合的多孔介质多尺度传输理论模型,阐明反应器内多尺度热质传输规律及与热化学动力性能的作用机制。采用计算流体力学软件FLUENT对于MgCl_2·6H_2O堆积床反应器中储热过程进行数值模拟。自定义编写化学反应过程中的质量和能量源项,用以描述反应器内热化学吸附／脱附过程的物质交换和能量传输过程。从FLUENT设置、模拟结果与实验对照、网格独立性检验等方面验证了热化学吸附模型的可靠性。基于本文建立的热化学反应传热传质模型,对MgCl_2·6H_2O堆积床反应器储热过程进行了模拟分析,得到不同时刻反应器中温度场、组分浓度场、固体颗粒含水量场的分布规律。综合分析了MgCl_2·6H_2O堆积床反应器储热过程中颗粒吸附量与水蒸气产率的变化特性,得出传质区的移动是与化学反应耦合的传热传质过程综合作用的结果,也是影响颗粒吸附量及水蒸气产率的关键因素。通过改变运行工况包括空气入口流速及反应床温度,对储热反应器的不同运行状态进行模拟分析。得出针对本文MgCl_2·6H_2O堆积床反应器,入口空气流速提高0.5倍,储热进程缩短41%；降低0.5倍,储热进程延长45%。床体初温降低20℃,脱附进程延长10%；床体初温升高10℃,脱附进程缩短8.5%。最后,本文总结了水合盐热化学吸附跨季节储热的技术特点,并指出了该技术未来的主要研究方向。
[Abstract]:In the cross-season heat storage technology, the thermal chemisorption of hydrated salt has the advantages of high heat storage density, long period storage without heat loss, clean and environmental protection, low cost and so on, and has gradually become the research hotspot in the field of heat storage at home and abroad.In this paper, the development of cross-season heat storage technology based on hydrated salt thermal chemisorption was investigated, and the heat storage characteristics of different hydrated salt thermal storage materials and the advantages and disadvantages of reactor selection were compared and analyzed.Because of the excellent reaction performance of the thermal storage material MgCl_2 6H_2O under low temperature operation conditions, combined with the requirement of numerical simulation in this paper, the pile-up bed reactor composed of MgCl_2 6H_2O granular material was selected as the simulation object.The thermochemical heat storage process on the surface of solid particle adsorbent in MgCl_2 6H_2O packed bed reactor was modeled theoretically, and the multi-scale transport theory model of porous media coupled with thermal chemical reaction was established.The multiscale heat and mass transfer in the reactor and the mechanism of its interaction with the thermochemical dynamic properties are described.The heat storage process in MgCl_2 6H_2O packed bed reactor was numerically simulated by computational fluid dynamics software FLUENT.The mass and energy source terms in the chemical reaction process are customized to describe the material exchange and energy transfer in the thermochemical adsorption / desorption process in the reactor.The reliability of the thermochemical adsorption model was verified from the FLUENT setting, the comparison between the simulation results and the experimental results, and the grid independence test.Based on the thermal chemical reaction heat and mass transfer model established in this paper, the heat storage process of MgCl_2 6H_2O packed bed reactor was simulated and analyzed. The distribution of temperature field, component concentration field and water content field of solid particles in the reactor at different times were obtained.The variation characteristics of particle adsorption capacity and water vapor yield during heat storage in MgCl_2 6H_2O packed bed reactor are comprehensively analyzed. It is concluded that the movement of mass transfer zone is a comprehensive result of heat and mass transfer process coupled with chemical reaction.It is also a key factor to influence the adsorption capacity and water vapor yield.By changing the operating conditions, including air inlet velocity and reaction bed temperature, the different operating conditions of the heat storage reactor were simulated and analyzed.For MgCl_2 6H_2O packed bed reactor, the inlet air velocity is increased 0.5 times, the heat storage process is shortened by 41 times, and the heat storage process is prolonged by 45 times.The initial temperature of the bed decreased by 20 鈩，

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