Study On The Characteristics Of An Auto-cascade Refrigeration System Using R744/R290 Or R744/R600a Natural Binary Mixture

Nowadays, people pay more and more attentions on ozone depletion and global warming, so it's an unreversed trend to use low ODP and GWP refrigerant in refrigeration industry. Natural mixtures have broad regard because of their friendly properties to entironment. R744, R290 and R600a have nice properties, the auto-cascade refrigeration system using their mixtures also can cancel their disadvantage, so this method becomes an important one in the area of refrigerant substitute.In this paper, proceeding from the actual thermodynamic definition, the calculation of R744/R290 and R744/R600a's thermodynamic properties are taken. The veracity and reliability of each calculation method and result are analyzed, appropriate equations are chosen, and the thermodyanamic properties of an auto-cascade refrigeration system and the factors which impact them are taken, a method how to choose the mole fraction of the mixture is taken. Results indicate that: R744/R600a is easier to separate phases than R744/R290, and adapt to work under lower pressure or higher temperature; after phases separated, the mole fraction of R744 is higher in gas and lower in liquid; the temperatures of bubble point and dew point become higher with higher pressure; in auto-cascade refrigeration system using natural binary mixture, it's necessary to consider refrigeration temperature, the pressure of condenser and evaporative condenser at the same time when choose the mole fraction of mixture; there is a optimal mole proportion between the gas and liquid at the exit of the condenser, which can make the low temperature branch condense adequately and make the high temperature branch vaporize adequately; appropriately higher heat exchanger coefficient can be helpful to lighten the heat load of evaporative condenser, enhance system capability.The presented conclusions which are obtained from numerical simulation provide theoretic gist for the study and application of the auto-cascade refrigeration system using R744/R290 and R744/600a. Furthermore, it's effective and useful for the studies of other mixtures and auto-cascade refrigeration system using other mixtures.