【作者】 杨硕；

【导师】 朱冬生；

【作者基本信息】 华南理工大学 ， 化学工程， 2010， 硕士

【摘要】 随着经济的迅速发展和人民生活水平的提高,能源和环境问题日益突出,不断利用新的节能技术来提高能源的利用效率是节约能源并实现可持续发展的必由之路。储能技术能够解决能量供求在时间和空间上不匹配的矛盾,因而是提高能源利用效率的有效手段。热泵技术以其节能和环保的优势在很多领域得到了广泛的应用,其在制取生活热水上的应用也越来越受到重视。把相变储能技术和热泵技术结合起来,研制相变储能式热泵热水器,实现优势互补,将有更大的节能空间和应用前景。本课题以相变储能式热泵热水器储能换热器为研究对象,采用理论分析、实验测试和数值模拟相结合的研究方法对其传热特性进行了深入系统的研究。主要研究工作包括以下几个方面:1、根据相变储能式热泵热水器的工作原理及相变储能材料(phase change material, PCM)的遴选原则,选取了合适的PCM。在对热泵热水器进行总体热量衡算的基础上设计了一种管翅式储能换热器,给出了储能换热器的具体结构参数。对储能换热器的传热特性进行了理论分析,采用了复合材料的理论模型对PCM侧的导热系数进行了分析,经分析指出PCM侧导热性能的改善是提高储能换热器传热性能的主要途径。2、对强化PCM相变传热特性进行了研究,通过在石蜡PCM中添加纳米铜制备纳米复合相变储能材料(nanocomposite phase change material, NC-PCM)来实现强化传热的目的。采用差示扫描量热法(DSC)测量了NC-PCM的相变潜热、相变温度。研究表明在纯石蜡中添加纳米铜颗粒,NC-PCM的相变潜热比纯石蜡略低,且随粒子浓度的增大逐渐减小,但相变温度变化不大;采用瞬态热线法测试了NC-PCM的固态和液态导热系数,结果表明导热系数随着随纳米颗粒含量的增大而增大,呈非线性关系。NC-PCM循环加热、冷却100次后,其热物性参数均改变不大,说明NC-PCM具有较好的热稳定性。对NC-PCM的相变传热进行了实验研究,采用温度-时间曲线法研究了不同纳米铜质量分数的NC-PCM的储、放热性能,采用红外摄像仪对其熔化和凝固过程的温度场分布进行了实时观察,结果表明在石蜡中加入纳米Cu粒子后,PCM的储、放热速率得到很大的提高。3、搭建了热泵热水器储能换热器性能测试实验台,模拟储能式热泵热水器的工作工况对储能换热器内部的温度场分布和出口水温进行了实验测试。在整个储能阶段和放热阶段,储能换热器处于非稳态条件下工作,其内部的换热过程是一个复杂的非稳态换热过程。对储能装置的出口水温进行了测量,结果发现储能装置进口水流量越大,PCM凝固速度越快,放热持续时间越短,由于相变材料绝大部分热量以潜热的形式释放,这使得出水温度大部分时间维持在一个恒定的温度范围,这是利用相变储热的优势所在。对制取的热水所含热量进行了计算,结果表明储能装置中的热量大部分已经释放出来,残余热量较小,用相变储能的热量利用效率要高于水的显热储能。4、根据设计的储能换热器建立了相应的物理模型和数学模型,利用Fluent6.2软件对储能换热器放热情况进行了二维、非稳态模拟,分析了各种结构参数对放热过程的影响。结果表明,采用翅片结构大大强化了相变过程的热量传递,各种结构参数储能换热器放热速率均有重要影响。这为储能换热器进一步优化设计提供了参考。更多还原

【Abstract】 With the rapid development of economy and the improvement of people’s living standard, the problem of energy and environment become more and more serious. One of the important ways to realize energy conservation and sustainable development is to develop new energy-saving technology. Energy storage technique can solve the contradiction that the energy supply and demand don’t match in time and space, so it’s a good way to improve energy efficiency. Heat pump technique is widely applied in many fields with its advantage of energy saving and environment-friendly. Its research on the hot water for domestic is becoming more and more important. Developing heat pump water heater with enerage storage system to combine the phase change thermal storage technology and heat pump technology will have a better future.The thesis focuses on the energy storage heat exchanger in heat pump heater. The heat transfer characteristics of the energy storage heat exchanger have been deeply researched by using the methods combined with theoretical analysis, experimental testing and numerical simulation in this paper. The main research work and conclusions include the following:1、On the grounds of the operation principle of the heat pump water heater with energy storage system and the selection principle of the phase change materials (PCMs), suitable PCM is chosen. A fin-tube energy storage heat exchanger is designed based on the total heat balance of the heat pump water heater and its concrete structure parameters are determined. The theoretical analysis on the heat transfer characteristics of the energy storage heat exchanger was presented and a theoretical model of composites was used to analyze the thermal conductivity of PCM. It is found that the thermal performance improvement of PCM is the main way to improve the heat transfer performance of energy storage heat exchanger.2、The enhanced heat transfer of PCM was studied by adding nano-copper to paraffin PCM to product nanocomposite phase change material(NC-PCM). Phase change temperature and latent heat of NC-PCM were measured with Differential Scanning Calorimetry (DSC). The DSC results reveal that the melting and solidification latent heats of NC-PCM shift to lower values compared with those of pure paraffin, however, the melting and freezing temperatures were almost the same as pure paraffin. The thermal conductivity of NC-PCMs was measured by a Hotdisk Thermal Constants Analyzer. The thermal conductivity of liquid and solid NC-PCM is enhanced approximately nonlinearly with the mass fraction of the copper nanoparticle. After 100 thermal cycles, The result indicates that the NC-PCMs have a good energy storage characteristic.The experimental study on the phase change of NC-PCM was carried. The temperature-time tests were conducted in order to verify the improvement of heat transfer rate in the presence of Cu particles. The Infrared Heat Camera was used to observe the temperature distribution in melting and solidification process. The results show that the heating and cooling rates of PCMs were significantly improved upon the addition of Cu nanoparticles.3、The performance of the energy storage heat exchanger of the heat pump water is tested. The internal temperature field and outlet water temperature of energy storage exchanger were measured by simulating the heat pump water heater working conditions. In the total heat charging and discharging stage, the heat transfer is a complex non-steady state process. The temperature of the outlet water is tested. The result shows the water discharge is higher, the heat release time is shorter. The heat releasing of PCM is mostly in form of latent heat, so the temperature of the outlet water maintained at a constant temperature range in most time. This is the advantage of utilizing PCM to store energy. The calculation results show that most of energy stored in the energy storage exchanger has been released. The heat utilization efficiency of latent thermal energy storage is higher than sensible heat of water.4、Based on the designed heat storage exchanger, physical model and mathematical model are built, and Fluent 6.2 is used to simulate the heat storage situation of the heat storage system. Different structural parameters influencing the releasing process were analyzed. The results show that the fin structure enhanced the process of phase change heat transfer, and various structural parameters of heat storage exchanger have an important effect on the heat releasing rate. The result can be direction and basis for the design optimization of the heat storage system.更多还原