自复叠热泵系统的理论分析与实验研究

发布时间：2018-06-06 05:49

本文选题：自复叠热泵系统 + 数值模拟　；参考：《青岛大学》2017年硕士论文

【摘要】：本文主要研究自复叠热泵系统结构改进。研究内容包括:自复叠热泵系统(火用)分析及循环热力计算;蒸发管数值模拟;冷凝器改进改进;自复叠热泵系统的实验研究。首先对实验系统做了(火用)分析及循环计算,计算结果表明,对于自复叠热泵系统而言,其(火用)损失主要集中在压缩机、节流机构、蒸发器及冷凝器上。考虑到对压缩机降低(火用)损失的困难,提出使用电子膨胀阀代替热力膨胀阀及增加回热器以提高节流机构的(火用)效率的节流机构改进方案。其次,对单根U型管内的蒸发问题进行了模拟。根据实际蒸发器内可能发生的问题,对纯R23制冷剂的管内蒸发及含有质量分数为8%R134a的R23混合制冷剂进行了数值模拟。模拟结果表明:纯R23制冷剂在管内蒸发时,管内的流型发展依次出现了泡状流、弹状流及环状流。对于含有8%R134a的R23混合制冷剂的模拟结果发现,其管内的蒸发速度明显低于纯R23制冷剂的管内蒸发速度。产生这种现象的原因是:混合制冷剂比纯制冷剂易于达到核态沸腾完全抑制状态,分界面上易挥发组分的蒸发,使得分界面饱和温度上升,减少了给汽泡生长提供热量的有效温差,同时混合物的传质阻力减缓了汽泡的生长率,削弱了核态沸腾,导致了混合物的抑制状态更容易达到,造成传热恶化。决定使用精馏器来代替汽液分离器以改善蒸发器的换热效果。根据非共沸混合工质在换热时其换热系数要低于纯组分工质的换热效果这一现象,本文提出在冷凝器上增加一个分离器来提高冷凝器的换热效果并使混合制冷剂充分分离的实验方案,在此实验方案的基础上,搭建了实验台。最后,对负载及空载时有无分离器及不同制冷剂充注比例时不同测量点的温度进行了实验测量,并对自复叠系统与两级压缩、喷气增焓系统进行了对比并观察了冷凝器内的流型变化。得到主要结论:经过分离后的非共沸工质所具有的最大传热温差及传热窄点现象得到了有效抑制,影响其换热的传质热阻也大大减小,同时经过分离器分离后的制冷剂与冷凝器的换热重新回到了换热开始阶段,制冷剂蒸汽能够与管壁直接接触提高了换热系数,并结合实际观测到的流型进行了验证。通过自复叠系统与其它几种系统的比较发现,自复叠系统在制冷量、功率、制冷系数等方面都优于其它几种系统。
[Abstract]:In this paper, the structure improvement of self-stack heat pump system is studied. The research contents include: exergy analysis and cycle thermodynamic calculation of self-stack heat pump system; numerical simulation of evaporator tube; improvement of condenser; experimental study of self-stack heat pump system. The exergy analysis and cyclic calculation of the experimental system show that the exergy loss is mainly concentrated on compressor, throttle mechanism, evaporator and condenser for the self-stack heat pump system. Considering the difficulty of reducing exergy loss of compressor, a scheme of improving throttling mechanism by using electronic expansion valve instead of thermal expansion valve and adding regenerator to improve the exergy efficiency of throttle mechanism is put forward. Secondly, the evaporation problem in a single U-tube is simulated. According to the possible problems in the actual evaporator, the evaporation of pure R23 refrigerant and the mixture of R23 refrigerant with mass fraction of 8%R134a are numerically simulated. The simulation results show that when pure R23 refrigerant evaporates in the tube, bubbly flow, slug flow and annular flow occur in turn. The simulation results of R23 refrigerant containing 8%R134a show that the evaporation rate in the tube is obviously lower than that in the pure R23 refrigerant. The reason for this phenomenon is that the mixed refrigerant is easier than the pure refrigerant to achieve the completely suppressed state of nucleate boiling, and the evaporation of volatile components on the boundary surface increases the saturation temperature of the interface. The effective temperature difference of heat supply for bubble growth is reduced, and the mass transfer resistance of the mixture slows down the growth rate of the bubble, weakens the nucleate boiling, and makes the inhibition state of the mixture easier to achieve, resulting in the deterioration of heat transfer. It was decided to replace the steam-liquid separator with a rectifier to improve the heat transfer efficiency of the evaporator. According to the phenomenon that the heat transfer coefficient of non-azeotropic working fluids is lower than that of pure working fluids, In this paper, an experimental scheme of adding a separator to the condenser to improve the heat transfer effect of the condenser and make the mixture refrigerant fully separate is proposed. On the basis of the experimental scheme, an experimental bench is built. Finally, the temperature of different measuring points under load and no-load with or without separators and different refrigerant filling ratios are measured experimentally, and the self-stacking system and two-stage compression are also studied. The jet enthalpy system was compared and the flow patterns in the condenser were observed. The main conclusions are as follows: the maximum heat transfer temperature difference and the heat transfer narrow point phenomenon of the separated non-azeotropic working fluid have been effectively restrained, and the heat transfer resistance affecting the heat transfer of the non-azeotropic working fluid has been greatly reduced. At the same time, the heat transfer of refrigerant and condenser after separating from the separator has returned to the initial stage of heat transfer, and the heat transfer coefficient of refrigerant steam can be increased by direct contact with the tube wall, which is verified by the actual observed flow pattern. It is found that the self-stacking system is superior to other systems in refrigeration capacity, power, refrigeration coefficient and so on.
【学位授予单位】：青岛大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU83

【参考文献】