Theory And Experiment Of Natural Refrigerant Mixture Used In Low Temperature Circuit Of Cascade Refrigeration

Industry refrigerant predominated by R13 has greatly damage effect on its ambient environment. For this, R13 has been phased out by the year 1996 in developed countries and before 2010 in developing countries. The alternative refrigerants of R13 such as R23 and R508b also have some disadvantages in the substitute process. And these alternative refrigerants are quite expensive. It is important to find alternative refrigerant which has good enveironmental, thermodynamical performance and low cost.Pure refrigerant which is friendly with ambient environment has some problems when used at low temperature. However, when mixed by two of them, the defects will be weakened and the merits will be swelled. And then the mixture will has good low temperature performance. In this paper, an environmental-friendly new alternative refrigerant was proposed, and performance of the new refrigerant was forcased in theory, and related experiments were carried out.At first, compositions of mixture were chosed from methane and ethane derivatives, natural refrigerants, and hydrocarbons refrigerants by environment performance, safty performance, physics and chemical performance, transmitting performance, thermodynamics and cycle performance. Then the binary mixture composed by R290 and CO₂ is considered as the best low temperature refrigerant.Second, freezing point temperature of mixture was found. Freezing point temperature of mixture moves up with the increasing of CO₂ fraction. In order to find the exact freezing point temperature at around -70℃, solid-liquid equilibrium model of non-idea solution was set up. The modifying of activity coefficient makes the solubility calculating more accurate. Influnced by the freezing point temperature of mixture, the fraction of CO₂ was limited in mixtures.The mixture ratio was determined. Based on the difference of thermodynamics, safety and cycle performance the mixture ratio of R290 and CO₂ was confirmed as 29% and 71%.By the organic combination of the least irreversible exergy loss method and com- -ponent exergy loss method, two exergy losses were obtained as follows: one was the least irreversible exchanging heat temperature difference and the least irreversible exergy loss, the other was the whole exergy loss of refrigeration system components. All of these gave the more accurate values for the system to improve its performance. Finally, at the cascade refrigeration sytem experiment table, experiments about diffent mixture ratio of R290 and CO₂ were done and then found the rules that cycle performance varied with the changing mixture ratio, and validated the new refrigerant chosed in theory. The experiments on the cycle performance comparison of R13 and the new refrigerant showed that the new refrigerant had more refrigeration capacities and COP. And the consecutive stability experiments showed that the new refrigerant was safety and stability.