关键词: 变流量制冷系统, 过热度振荡, 稳定性, 压比, 阀开度

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