纳米制冷剂管内强化换热研究

发布时间：2018-08-12 07:27

【摘要】：纳米制冷剂是在纳米流体的概念上提出来的，他们之间主要区别就在于基液的不同，纳米制冷剂采用的是气化能力更强的制冷剂。我们按照一定的质量分数，将纳米颗粒添加到制冷剂中，制备成新型、高效的换热工质。纳米制冷剂的导热系数高，而且其稳定性好、对设备的磨损也小，这为开发适用于纳米制冷剂的换热器提出了新的方向。基于此，本文研究了五种纳米制冷剂的稳定性，并分别这对五种纳米制冷剂在三种不同类型的管内进行了沸腾换热实验研究。本文采用物理法和化学法相结合的方法制备纳米制冷剂，将制备好的纳米颗粒按照一定的比例添加到制冷剂中，然后添加表面分散剂，防止其产生团聚的现象，然后利用超声波振荡使其形成稳定的悬浮液。利用目测法和对比透射比法来评价纳米制冷剂的稳定性，发现当浓度相同时，添加表面分散剂的纳米制冷剂的稳定性差别不大；而未添加表面分散剂的纳米制冷剂的稳定性很不好，稳定性和密度成基本成反比。纳米制冷剂管内流动沸腾换热实验结果表明：同一质量流量下，随着纳米颗粒质量分数的增加，，纳米制冷剂的传热系数变大，增幅与纳米颗粒的质量分数基本成线性关系；纳米颗粒的质量分数是影响纳米制冷剂强化传热性能的主要因素；不同纳米颗粒对纳米制冷剂的传热性能影响不一样；纳米颗粒本身热导率大的，其制备成的纳米制冷剂的强化传热性能更好一些；纳米制冷剂的传热系数随着干度的增大而增大。但干度在0.5和0.6之间时，纳米制冷剂的传热系数增加的幅度最大。
[Abstract]:Nanometer refrigerant is put forward in the concept of nanometer fluid. The main difference between them lies in the difference of base liquid. The nanometer refrigerant uses refrigerant with stronger gasification ability. According to a certain mass fraction, the nanoparticles were added to the refrigerant to prepare a new and efficient heat transfer medium. The thermal conductivity of nano-refrigerant is high, and its stability is good, and the wear of the equipment is also small, which provides a new direction for the development of the heat exchanger suitable for nano-refrigerant. Based on this, the stability of five nanocrystalline refrigerants was studied, and the boiling heat transfer experiments of five nano-refrigerants in three different types of tubes were carried out. In this paper, nanometer refrigerants are prepared by combining physical and chemical methods. The prepared nanoparticles are added to the refrigerant in a certain proportion, and then surface dispersants are added to prevent the agglomeration. Then ultrasonic oscillation is used to form a stable suspension. The stability of nano-refrigerant was evaluated by visual method and contrast transmittance method. It was found that the stability of nano-refrigerant with surface dispersant was not different when the concentration was the same. However, the stability of nano-refrigerant without surface dispersant is very poor, and the stability is inversely proportional to the density. The experimental results of flow boiling heat transfer in nano-refrigerant tube show that the heat transfer coefficient of nano-refrigerant increases with the increase of mass fraction of nano-particles at the same mass flow rate, and the increase is basically linear with the mass fraction of nano-particles. The mass fraction of nanocrystalline particles is the main factor affecting the enhancement of heat transfer performance of nano-refrigerants; the effects of different nanoparticles on the heat transfer properties of nano-refrigerants are different; the thermal conductivity of nanocrystalline particles is large, The enhanced heat transfer performance of the prepared nano-refrigerant is better, and the heat transfer coefficient of the nano-refrigerant increases with the increase of dryness. However, when the dryness is between 0.5 and 0.6, the increase of the heat transfer coefficient of the nano-refrigerant is the largest.
【学位授予单位】：东北电力大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB611

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