Experimental Researches On Two Different Heat Transfer Pinch Points Of Non-azeotropic Mixtures Of Natural Refrigerants In High Temperature Heat Pump

Based on the two attributes of non-azeotrpic refrigerates: temperature glide and relationships between temperature and enthalpy, a high temperature water source heat pump system was set up and theoretical investigations and experimental researches were carried on to validate the two different pinch points.From the view of the first kind of pinch point, experimental researches were carried out with a binary mixture composed of R290 and R600 which is named Z1 (17%R290/83% R600, mass ratio) in the heat pump system. Results show, similarly to theoretical computations, maximum temperature differences occurred in the condenser, and pinch points occurred in the evaporator, their numerical values and locations within the heat exchanger changed when the fluxes of water altered. Kept conditions in the evaporator side constantly, occurrences of maximum temperature differences would reduce the cycle efficiency of the system; simultaneously, kept conditions in the evaporator side constantly, occurrences of pinch points in the evaporator would enhance the cycle efficiency of the system. Extended to other mixtures whose relationships between temperature and enthalpy in phase change region varied, the pinch points and the maximum temperature differences would still occur in the heat exchangers, and they also impacted the cycle efficiency in the same way, i.e. the appearances of the maximum temperature differences would reduced the cycle efficiency, but they could appropriately reduce the heat transfer area of the heat exchangers; correspondingly, the appearances of the pinch points would enhance the cycle efficiency, but they required larger heat transfer area. Consequently, whether to avoid the occurrences of the pinch points and the maximum temperature differences or not, it was an integrated problem of application conditions(air-condition or heat pump), the cycle efficiency and heat transfer area.Then experimental researches aiming at problem of the second king of pinch points were carried out applying Z1 and Z2 (50%R290/50% R600, mass ratio). The occurrences of the pinch points mean that working fluid in condenser could not be condensed completely, which could bring a lot of problems of instability. To address these problems, researches aiming at non-steady state and steady state were involved. Results showed that, under steady state conditions, working fluid processing in condensation could be condensed completely. But only in the condenser, it was possible that working fluid could not be condensed completely, because, working fluid which was not condensed completely in the condenser could be condensed completely in the pipeline connecting the condenser or in the refrigerant receiver. This phenomenon should be avoid to prevent the heat capacity and cycle efficiency from reducing. In the non-steady state conditions, the second kind of heat transfer pinch points occurred, phenomenon that working fluid in the condenser was condensed incompletely appeared.