The Heat Transfer Characteristics And Composition Shift Research Of Zeotropic Refrigerant In Tube-to-tube Evaporator

Due to pinch points and composition shift are easily occur in zeotropic refrigerants’practical applications, the two aspects further analyzing pinch point theory and investigating the gravity impact for composition shift of fluid reservoir using a simulating way are provided in this paper.Firstly, because of the heat transfer fluids’internal relations in energy balance equation, a simple two-fluid geometric model is established through tensile and translation method. Through abstracting the geometric model, the decisive influence variables of pinch point or the maximum temperature difference are revealed, that are flow ratio k (mass flow ratio, refrigerant:water) and inlet temperature of water.Secondly, the maximum temperature difference experiments utilizing R290/R600 (mass fraction 0.85/0.15) as working fluid are carried out. By comparing experimental results with theoretical model, the consistency conclusions are given: as the flow ratio k increases, it is called a contrarotating property the temperature difference will present contrarotating phenomenon along the evaporator; it is called the maximum temperature difference’migration law the position of the maximum temperature difference moves to the dew point of refrigerant in evaporator, when the flow ratio k increasing(as two phase region’relative scale for reference); it is called translation property the temperature difference along the evaporator will present upward translation phenomenon with the inlet temperature of water increases. In addition, experimental study of two phase region length and specific enthalpy’distribution along the evaporator is carried out by different experimental parameters.Again, by experimental investigation of the phase change characteristics of pure refrigerants and refrigerant mixtures, it has shown that the working fluids in the evaporation process have a unique nature: that is, the processes of working fluids’phase change occur in the vast majority of the early and the late, and in the least minority of the middle. Furthermore, this nature will not change whether the refrigerant is mixture or not. And, mixed refrigerant in the phase transition has a tendency that is the high boiling point refrigerant evaporates after low boiling point refrigerant. Finally, a gravity tube’s composition shift theory is conducted by taking the thermodynamic equilibrium as the point of departure. Experiments select two types butane and pentane mixtures for large mass fraction of butane and low mass fraction of butane, and set the gravity tube’inclination angles for 90°and 45°. The analysis result shows that: looking down the gravity tube, the mass fraction of low boiling point refrigerant tends to decrease in the liquid phase, and the influence becomes more weak as the place close to the bottom of the gravity tube. It is also found: for the binary mixture having large mass fraction of more volatile fluid, the composition shift will present decrease as the gravity tube’angle decreases; for the binary mixture having low mass fraction of more volatile fluid, the composition shift will present increase as the gravity tube’angle decreases.