Abstract: Aiming at the phenomenon of superheat instability in variable refrigerant flow(VRF)system,the experiment was designed by using variable flow water-cooled refrigeration unit. By observing the hunting phenomena at the same frequency of the important parameters of the relevant system,the hunting mechanism of the superheat of the unstable section was analyzed and the conclusion was drawn. The experimental results showed that with the liquid phase elongation in the evaporator,the evaporation point is continuously driven to the outlet of the evaporator in the case of a certain amount of evaporation capacity,and the system shows the initial hunting state. When the superheat enters the unstable region of the the minimum stable signal(MSS)line,the heat transfer mechanism on both sides of the evaporator alternates due to the change of refrigerant flow pattern,thus it has the instability. Under the same frequency,the influence of the valve opening on the mass flow rate is only about 53.3% of the transformer pressure ratio,but the maximum peak-valley difference between the two kinds of working conditions can reach about 3K in the unstable region. Under the condition of 1^#,the pressure ratio has a more direct impact on the energy consumption of the compressor,and the coefficient of performance(COP)can reduce under the premise of the increase of the refrigerating capacity.

Key words: variable refrigerant flow refrigeration system, superheat oscillation, stability, pressure ratio, valve opening

摘要： 针对变制冷剂流量（VRF）系统中的过热度不稳定性振荡现象，利用变流量水冷式制冷机组设计实验。通过观察同一频率下定阀开度变压比和定压比变阀开度时系统参数的振荡现象，分析不稳定段过热度振荡机理，并得出结论。实验结果表明：随着蒸发器内液相拉长，在蒸发量一定的情况下，完全蒸干点不断地向蒸发器出口推移，系统呈现出振荡初态；当过热度跨入最小稳定信号（MSS）线的不稳定区域时，由于制冷剂流型的变化使得蒸发器两侧换热机理发生交替，从而产生了不稳定性振荡；变阀开度对质量流量的增量影响仅为变压比下的53.3%，但两工况下能够在不稳定区间达到的最大峰谷差均在3K左右；工况1^#下压比对压缩机功耗有更直接的影响，在制冷量微升的前提下仍能促使系统性能系数（COP）趋势向下。

关键词: 变流量制冷系统, 过热度振荡, 稳定性, 压比, 阀开度