Theoretical And Experimental Study On The Miscibility Of Refrigerants With Lubricants

With many countries in the world paying close attention to climate problems, some refrigerants with high ozone depletion potential and global warming potential are gradually eliminated from the refrigeration trade. The miscibility of refrigerants with refrigeration oils has large influence on the working effect of the refrigeration system. Therefore, it is necessary to study the refrigerants miscibility with oils by both experimental and theoretical methods in order to generalize the use of environmental-friendly refrigerants.The solubility lines of refrigerants with refrigeration oils are simulated by cubic equation of state and activity index methods in this thesis. Then critical solubility temperature lines are predicted on the basis of simulative solubility lines. Through comparative analysis of the miscibility difference among many refrigerants, a new method combining the solubility parameter and empirical formula methods is proposed. This new evaluation method is applied to evaluate the miscibility degree of 18 pure refrigerants with the mineral oil. The result shows that this method has merits of both solubility parameter and empirical formula methods, which adapts to more kinds of refrigerants than empirical formula method and is more accurate than solubility parameter method.An experimental apparatus for testing the miscibility of refrigerants with lubricants is established based on relative standards. The miscibility of some pure refrigerants with oils is tested. In nearly 15% oil rate, RE170/R227 ea with a mineral oil, RE170/R1234ze(E) with a mineral oil are also tested. The experimental results show that CF3 I, RE170, R161 have good miscibility with the mineral oil; R134 a, R227 ea, R152 a also have good miscibility with POE oils. When the mass fraction of R227 ea in RE170+R227ea blends varies from 38% to 55%, the critical solubility temperature has a rapid increase. In the RE170+R227ea and mineral oil refrigeration system, the mass fraction of R227 ea in the binary mixture should not exceed 50% in order to avoid blocking pipe lines or decreasing coefficient of performance. When the mass fraction of R1234ze(E) in the mixture of RE170+R1234ze(E) varies from 31% to 70%, the critical solubility temperature has a rapid increase. Once the rate of R1234ze(E) exceeds 70%, large flocs may appear even in room temperature. Therefore, it is suggested that the mass fraction of R1234ze(E) in the binary mixture is not more than 60%. In nearly 15% oil rate, two methods including empirical formula method and new discriminant weighting method are proposed to evaluate the miscibility degree of refrigerant mixture with the mineral oil. Both methods are exact comparing with the experiment result. Empirical formula method is practical and new discriminant weighting method owns some theoretical value.In different oil rates, the miscibility of R600a+R227ea with a mineral oil, R600a+R1234ze(E) with a mineral oil are tested. A triangle diagram is proposed to show the miscibility degree of binary refrigerants with one kind of oil. This diagram takes the mass fraction of binary refrigerants and oil as the coordinates to describe the influence of every component rate on the miscibility degree. In R600a+R227ea and mineral oil solution, if R600 a rate is less than 20%, two phases will arise even in low oil rate and room temperature. If R600 a rate exceeds 35%, this phenomenon will not appear. In R600a+R1234ze(E) and mineral oil solution, when R600 a rate varies between 10% and 25%, critical solubility temperature changes greatly. If R600 a rate is less than 10%, two phases will arise even in low oil rate and room temperature.