R32和R1234ze在水平细管道内的冷凝换热特性研究
发布时间：2018-11-27 09:37
【摘要】：随着环境问题的日益突出，制冷剂的替代问题也备受人们关注，新型低GWP和零ODP制冷工质的研究成为了热点课题。R32和R1234ze因其具有较好的热力学性质和环保性能，成为了较为理想的替代品。另一方面，换热的微小型化也已成为一种必然的发展趋势。随着管径的减小，重力、表面张力和切应力对换热影响的相对大小也发生变化，从而引起换热时流型的转换与常规通道不同，导致小通道内的换热机理和压降特性与常规通道不同。因此，有必要进行实验，对小通道内换热机理的研究提供数据基础与理论支持。 本文用R32、R1234ze两种制冷剂在2mm水平细圆管内进行了冷凝换热实验，实验时工质流量为100-400kg/m2，饱和温度设定为40℃、45℃和50℃，热流密度范围为4-30kW/m2，干度变化范围为0~1。实验测得了R32、R1234ze在不同工况条件下冷凝换热系数和压降，并观测了R32两相流的流型特性。 分析实验结果，发现R1234ze和R32的冷凝换热系数范围分别在1.5~8kW/m2K和1~10kW/m2K之间，并且随干度的增加而增加，随饱和温度的升高而降低，，随质量流量的增加而增大。测试段入口干度和热流密度的变化对换热系数的影响不太大。管内摩擦压降随质量流量增加而增大，随饱和温度的升高而降低，而且质量流量越大时，这种影响越明显。对R32流型实验观测中，观察到了塞状流、弹状流、环波状流和环状流。并发现随着干度的增加，流型逐渐由间歇流转换为环波状流，最后到环状流。而且随着质量流量的增大，由间歇流转换到环波状流时的干度变小。 通过对比R32、R134a分别在不同管径下的换热系数，发现换热系数随着管径的减小而增大。对比了R1234ze、R32、R1234yf和R134a四种制冷工质在相同实验工况下的换热系数，发现R32的冷凝换热系数最高， R1234ze与R1234yf的换热系数大小比较接近，且都比R134a、R32小。 将本次实验结果与六种经典换热预测模型、四种压降预测模型和五种经典流型图模型进行了对比。发现对换热系数预测较好的是Baird模型和Gerimella模型，对摩擦压降预测较好的是Muller-Heck模型和Chisholm模型，并用这四个模型对其它文献中的数据进行了预测与分析。对流型图预测较好的是Yang-Shieh经验流型图。同时引用无量纲数Xtt, Bd, Re，提出了一种新的由间歇流与环波状流之间过渡曲线的预测公式。
[Abstract]:With the increasingly prominent environmental problems, the problem of refrigerant substitution has attracted much attention. The research of new low GWP and zero ODP refrigerants has become a hot topic. R32 and R1234ze have better thermodynamic properties and environmental protection properties. Has become the more ideal substitute. On the other hand, the micro-miniaturization of heat transfer has become an inevitable trend of development. With the decrease of pipe diameter, the relative magnitude of the influence of gravity, surface tension and shear stress on heat transfer also changes. The heat transfer mechanism and pressure drop characteristics in small channels are different from those in conventional channels. Therefore, it is necessary to carry out experiments to provide data basis and theoretical support for the study of heat transfer mechanism in small channels. In this paper, the condensation and heat transfer experiments were carried out in a 2mm horizontal thin tube with two refrigerants R32O / R1234ze. The working fluid flow rate was 100-400 kg / m ~ (2), the saturation temperature was 40 鈩
本文编号：2360247
[Abstract]:With the increasingly prominent environmental problems, the problem of refrigerant substitution has attracted much attention. The research of new low GWP and zero ODP refrigerants has become a hot topic. R32 and R1234ze have better thermodynamic properties and environmental protection properties. Has become the more ideal substitute. On the other hand, the micro-miniaturization of heat transfer has become an inevitable trend of development. With the decrease of pipe diameter, the relative magnitude of the influence of gravity, surface tension and shear stress on heat transfer also changes. The heat transfer mechanism and pressure drop characteristics in small channels are different from those in conventional channels. Therefore, it is necessary to carry out experiments to provide data basis and theoretical support for the study of heat transfer mechanism in small channels. In this paper, the condensation and heat transfer experiments were carried out in a 2mm horizontal thin tube with two refrigerants R32O / R1234ze. The working fluid flow rate was 100-400 kg / m ~ (2), the saturation temperature was 40 鈩
本文编号：2360247
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