潜热型控温包装系统传热模型与试验研究

发布时间：2018-09-04 08:10

【摘要】：物流环境温度的控制是保障温度敏感型产品物流过程质量与安全的关键因素。以控温包装为基础的无源冷链物流技术,是实现产品物流控温特别是保证物流“最后一公里”控温的有效技术手段。控温机理、控温包装设计方法、蓄冷剂性能改善与表征是设计优化无源控温包装系统的关键。本课题以潜热型控温包装系统为研究对象,开展蓄冷剂导热性能改良技术方法与性能表征的研究,探讨控温包装相变传热机理与理论,建立控温包装相变传热模型;在此基础上,构建控温包装可靠边界,提出控温包装设计方法。研究内容主要包括:(1)蓄冷剂导热性能优化及分散体系有效导热系数建模通过向液体蓄冷剂中掺杂高导热粉末(铝粉、铜粉和石墨粉),向相变微胶囊蓄冷剂(micro-PCMs)中掺杂导热液(水)的方法,研究掺杂物对蓄冷剂有效导热系数的影响。结果表明,液体蓄冷剂的有效导热系数随粉末掺杂量的增加而增加,但体系中粉末质量分数达到临界值后,体系有效导热系数显著下降;micro-PCMs的有效导热系数随导热液增加而增大,但体系中micro-PCMs的质量分数小于临界值后,体系有效导热系数的增加速率显著减缓。以掺杂石墨粉的改性蓄冷剂为例,研究掺杂对蓄冷速度与控温性能的影响。结果表明,在主蓄冷剂量相同的情况下,增加蓄冷剂有效导热系数,蓄冷剂凝固速度加快,而对控温时间的影响不显著。由试验结果发现,当分散相质量分数高于临界值后,体系中将出现气相成分,并显著降低体系的导热系数。为此,提出了高分散相质量分数下分散体系有效导热系数预测建模方法,并基于分形理论和渝渗理论建立用于预测高分散相质量分数下分散体系有效导热系数的FP模型,并通过试验验证了模型的有效性。最后,基于FP模型对分散体系有效导热系数预测模型进行了统一表征,构建了固-液-气三相分散体系有效导热系数分布图。(2)建立控温包装一维相变模型基于Fourier导热定律和能量守恒定律,建立恒温和变温条件下控温包装一维相变传热模型。该模型可在未知表面传热系数的情况下通过迭代运算,获得PCM内部温度场分布,同时计算表面传热系数。基于一维相变传热模型,讨论分析隔热壁导热系数wk、PCM导热系数lk、过余温度y、隔热壁厚度b、PCM相变潜热L以及变温环境对相变传热过程的影响。结果表明,表面传热系数主要受隔热壁导热系数wk、过余温度y和壁厚b的影响;固-液界面移动速度主要受到隔热壁导热系数wk、过余温度y、壁厚b以及PCM相变潜热L的影响;而PCM导热系数lk则对表面传热系数和固-液界面移动速度均没有显著影响。此外,当PCM导热系数远大于隔热壁导热系数时(/10l wk k),固-液界面移动速度近似为常数,当PCM导热系数小于隔热壁导热系数或与隔热壁导热系数相当时,固-液界面移动速度随时间推移而减缓。变温环境下的相变传热过程可近似简化成若干个恒温环境下相变传热过程的线性叠加。为验证控温包装一维相变传热模型,首先将恒温条件下的一维相变传热模型与经典的比较。结果表明,本文模型退化解与Neumann解析解结果一致,Neumann解析解是本文模型的一种特殊情况;本文模型结果与Mehling模型的计算结果一致。其次,通过自制的一维相变传热试验装置进行了一维相变传热试验。结果表明,在PCM融化初期,本文所建立的一维相变传热模型能够有效描述一维相变传热过程。(3)提出控温包装控温时间预测模型根据构建的一维相变传热模型及其规律,建立控温包装表面传热系数、保温容器系统热阻的经验公式,并进一步建立控温包装控温时间预测模型,通过相应产品的储藏试验验证模型。(4)提出控温包装可靠边界及设计方法结合控温包装控温时间预测模型,提出了控温包装可靠边界概念与构建方法,进而提出了控温包装设计方法。根据控温包装设计方法开发控温包装的设计评估软件
[Abstract]:Temperature control of logistics environment is the key factor to ensure the quality and safety of temperature-sensitive product logistics process.Passive cold chain logistics technology based on temperature-controlled packaging is an effective means to realize product logistics temperature control, especially to ensure the "last kilometer" temperature control of logistics. Improvement and characterization is the key to design and optimize the passive temperature-controlled packaging system.Based on the latent heat-controlled packaging system as the research object, the research on improving the thermal conductivity and performance characterization of refrigerant storage was carried out, the mechanism and theory of phase change heat transfer in temperature-controlled packaging were discussed, and the phase change heat transfer model of temperature-controlled packaging was established. The main research contents include: (1) Optimizing the thermal conductivity of the regenerant and modeling the effective thermal conductivity of the dispersion system by doping high thermal conductivity powder (aluminum powder, copper powder and graphite powder) into the liquid regenerator, and doping the thermal conductivity liquid (water) into the phase change microcapsule regenerator (micro-PCMs). The effect of dopants on the effective thermal conductivity of the regenerator was studied. The results showed that the effective thermal conductivity of the liquid regenerator increased with the increase of the powder content, but the effective thermal conductivity of the system decreased significantly when the powder content reached the critical value. When the mass fraction of icro-PCMs is less than the critical value, the increase rate of the effective thermal conductivity of the system decreases significantly. Taking the modified regenerator doped with graphite powder as an example, the effect of doping on the storage rate and temperature control performance is studied. The experimental results show that when the mass fraction of dispersed phase is higher than the critical value, the vapor phase will appear in the system and the thermal conductivity of the system will be significantly reduced. In this paper, a FP model for predicting the effective thermal conductivity of the disperse system with high disperse phase mass fraction is established, and the validity of the model is verified by experiments. Finally, the prediction model of the effective thermal conductivity of the disperse system is unified and characterized based on the FP model, and the distribution diagram of the effective thermal conductivity of the solid-liquid-gas three-phase disperse system is constructed. Based on Fourier's law of heat conduction and conservation of energy, a one-dimensional phase change heat transfer model for temperature-controlled packaging under constant and variable temperature conditions was established. The results show that the surface heat transfer coefficient is mainly affected b y the thermal conductivity of the insulating wall wk, the excess temperature y, the thickness of the insulating wall b, the latent heat L of PCM and the variable temperature environment. The wall thermal conductivity wk, excess temperature y, wall thickness B and PCM latent heat L have no significant effect on the surface heat transfer coefficient and the moving speed of solid-liquid interface. The moving velocity of the solid-liquid interface decreases with time when the thermal conductivity of the insulating wall is equal to that of the insulating wall. The phase change heat transfer process in the variable temperature environment can be approximately simplified as a linear superposition of several phase change heat transfer processes in the constant temperature environment. The results show that the degenerate solution of the model is in agreement with the Neumann analytical solution, and the Neumann analytical solution is a special case of the model. The results of the model are in agreement with those of the Mehling model. Secondly, a one-dimensional phase change heat transfer test is carried out by a self-made one-dimensional phase change heat transfer test facility. The results show that the one-dimensional phase change heat transfer model established in this paper can effectively describe the one-dimensional phase change heat transfer process in the initial stage of PCM melting. (3) According to the one-dimensional phase change heat transfer model and its regularity, the one-dimensional phase change heat transfer model for temperature control packaging is proposed, and the empirical formulas of heat transfer coefficient on the surface of temperature control packaging and thermal resistance of insulation container system are established. (4) Propose the reliable boundary and design method of temperature-controlled packaging combined with the time prediction model of temperature-controlled packaging, put forward the concept and construction method of reliable boundary of temperature-controlled packaging, and then put forward the design method of temperature-controlled packaging. Design method to develop temperature control package design evaluation software
【学位授予单位】：江南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB486

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