【作者】 包华汕；

【导师】 王如竹；

【作者基本信息】 上海交通大学 ， 制冷与低温工程， 2011， 博士

【摘要】 热化学吸附有一种优化循环称为再吸附制冷循环,其采用两个填充有不同吸附盐的吸附床。在相同的压力情况下,这两种吸附盐与反应气体有着不同的反应平衡温度,因此被分别称为高温盐和低温盐,系统利用低温盐与反应气体的反应解吸热来产生制冷效果。一般化学反应解吸热是氨相变热的2倍之多,所以理论上再吸附系统与传统吸附系统相比制冷量有所提高。除此之外,再吸附系统减少了由于传统吸附压力过高所带来的安全隐患;无液态制冷剂的存在使得系统抗振动颠簸能力增强,甚至可不受重力因素的影响,因此可在机动车、渔船甚至太空船等领域得到更广泛的应用。合理正确挑选吸附工质对是再吸附制冷循环系统实现低品位热源高效利用以及提高化学吸附制冷效率的关键问题之一,本课题首先对再吸附制冷吸附工质对的配位物特性、热平衡性质以及化学反应动力特性等进行研究分析,提出了针对不同的实际应用需求对再吸附工质对进行正确选择的参考依据。随后,结合以上吸附工质对挑选原则,为实现制冷温度达到0℃以及0℃以下的再吸附制冷循环系统构建,先对挑选出的三种低温盐氯化钡、溴化钠、氯化铵分别与高温盐氯化锰组合的再吸附原型小系统进行实验对比研究,并结合膨胀石墨为基质的混合固化吸附剂传热传质强化技术,通过对吸附盐-氨的吸附/解吸性能、热动力平衡性质的研究,结果表明工质对氯化铵-氨/氯化锰-氨的优越工作性能,其COP（制冷效率）与SCP（单位质量吸附剂的制冷功率）都胜出于其他所研究的组合,是0℃以及0℃以下再吸附制冷的最佳选择。由于氯化铵是新颖的再吸附反应盐,本课题还通过实验研究获取氯化铵混合吸附剂在基础物性以及氯化铵氨络合物的化学反应动力方面仍缺少的数据信息,在原有经典化学吸附动力模型基础上进行修正,分别建立氯化铵氨络合物合成和分解反应速率方程,将其表达成反应速率同时与热平衡压差和热平衡温差的函数关系式。于是,结合以上成果建立再吸附制冷循环系统的整体仿真模型,发现模拟结果在化学反应动力特性方面体现出了与实验数据极为吻合的变化趋势,由此证明了该反应速率方程的适用性。为了验证所选氯化铵作为再吸附低温盐的优越性能,将再吸附制冷循环应用于33 L的家用小型蓄冷冰箱中,通过实验测量在20 35℃室温下3小时内的制冰量,得到该装置单位质量氯化铵的总制冷量,约为475 kJ·kg^-1,并且同时实现-1 6℃冷藏和-16 -14.5℃冷冻的两个功能。小型冰箱的实验结果更加突显出几个优化目标的重要性:减小金属热容比例,加强系统的换热效率以及装置保温性能。根据尽量减少金属部件的质量比例以及提高系统换热效率的优化设计,应用氯化铵-氨/氯化锰-氨工质对的单级再吸附制冷实验系统装置在150℃的热源驱动和20℃的环境温度下,完成了-15 5℃的制冷性能测试。当反应气体流动阻力可忽略不计制冷温度为-15℃ 5℃时,系统COP和SCP分别为0.24 0.31和260 350 W·kg^-1。该再吸附制冷系统达到了目前国际研究成果所未有的制冷低温,且COP与目前最高水平相比提高了1.55倍。反应气体传输时的流动阻力使得系统能够在某一固定制冷功率值上较为平稳和持久地输出冷量,但由于流动压降的损失造成部分制冷量的损失。另外发现,再吸附工质对氯化铵-氨/氯化锰-氨在制冷温度为0℃工况下达到了最佳匹配状态,通过对工质对热化学反应动力特性的深入分析,并结合之前的系统模拟仿真计算,确定并验证了这对工质对的匹配原则数学关系式。此关系式不仅可以作为系统初步构建设计的参考工具,也是系统优化设计的预测依据。更多还原

【Abstract】 Resorption is an optim um cycle of therm o-chemical adsorption. It adopts two adsorbent beds filled with two dif ferent reactive salts. Since under the sam e working pres sure the equilibrium temperatures of the t wo employed reactive salts reactin g with the sam e gas （ammonia） are different, these two salts are named as high tem perature salt （HTS） and lo w temperature salt （LTS）. The decomposition of the LTS complex yields the cooling effect. Due to the decomposition heat lar ger than vaporiz ation enthalpy of refrigerant, the cooling capacity of the resorption system is theoretically lar ger than that of the conversional adsorption system. Besides, the fact that th e working pressure in resorption system is relatively lower comparing to the traditiona l adsorption system, mitigates the dangerous introduced by the high pressure; the application of resorption system can be extended to the vehicle, fish boat and even the spacecraft because there is no liquid phase refrigerant inside, the system is not sensitive to the vibration as well as the gravity.Rational and wise selection of the working pair s is one of the key strategies for enhancing the utilization rate of the low grad e thermal energy source and the co oling efficiency of the resorption systems. This work firstly carried out the inve stigated on the characteristics , thermodynamic equilibrium and reaction k inetic properties of ammoni ate complexes, thus some guides for seeking proper reactive salts acco rding to a certain practical requirem ent of resorption refrigeration were proposed.Afterwards, with the combination of the selection criterions of the working pairs and the aim for cooling at 0℃or lower than 0℃, three reactive salts BaCl₂, NaBr, and NH₄Cl were picked up as LTS to coupling-work with MnCl₂ acting as HTS. They comprised three kinds of resorption prototypes, the performance of wh ich were investigated and com pared under different conditions, leading to the conclusi on that, when the coo ling temperature was required at 0℃or lower than 0℃, NH₄Cl was the best choice of LTS when MnCl₂ was HTS. The prototype with NH 4Cl achieved the highest COP and SCP among all the prototypes studied.Since NH₄Cl was a novel salt for sorption cycle and has been rarely reported so far, in order to built the global modelling of the resorption system employing NH₄Cl/ MnCl₂, the basic physical characteristics of NH 4Cl compound sorbent with expanded graphite as well as the kinetic model were experim ental studied in this work. Due to take the influence of a pseudo-equilibrium zone on the reaction process into consideration, a revised kinetic model based on the classic ones for chemisorptions and with both equilibrium temperature drop and equilibrium pressure drop being involved into was proposed expres sly for NH₄Cl complex. The reasonable results obtained by the global model using such a kinetic equation had good agreement with the experimental results.The resorption system using NH₄Cl as LTS and MnCl₂ as HTS was applied to a refrigerator with a 33 L cold storage box, with the objective of validating the advantage of NH₄Cl as LTS. The refrigerator provided two levels of cool ing effect: the bottom zone insid e of the refrigerator box the minimal temperature reached -16 -14℃and the air was kept under -10 oC for about 3 h; the upper zone inside could be cooled down to -1 6℃. However, the drawbacks exposed by this refrigerator em phasized the n ecessity of system optimization, including reduction of m etallic heat load p roportion and enhancement of heat transfer efficiency.Based on the proposed optim ization strategies, a bench-scale therm ochemical resorption system with the workin g pair MnC l2/NH3 and NH 4Cl/NH3 was built up and inve stigated under different conditions to demonstrate the feasibility of sub-zero refrigeration. When the flow resistance of the reactiv e gas could be neglected, th e resorption system achieved COP and SCP, respectively, 0.24 0.31 and 260 350 W per kg of NH₄Cl when refrigeration temperature was at -15 5℃. Such cooling level achieved by resorption system s has been never reported before, moreover, the COP was increased by 1.55 tim es. If the transm ission resistance of the reactive gas was high e nough to produce pronounced pressure drop, the system could output cooling ef fect at a certain point m ore steady and longer though, at the same time it sacrificed some cooling capacity. Additionally, a match performance between HTS and L TS complexes when refrigerating at 0℃was discussed based on the adsorption/desorption capacity and thermodynamic equilibrium property. A mathematical expression of the match behavior was proposed and validated by the simulative results of the global system modeling.更多还原