Optimization of the Capillary Tube for Domestic Refrigerator With Mixture of Propane and Isobutene as Refrigerant

The hydrocarbon mixture of R290/R600a with mass ratio of 50/50 is regarded as a promising long-term refrigerant to replace R12 in domestic refrigerators since it can potentially provide higher COP than R12 system under the same operating conditions. In practical application, the length of the capillary tube should be matched with this alternative mixture; otherwise, the refrigerator system can probably consume more energy than the R12 system. In this paper, a simulation model of adiabatic capillary tube, in which some empirical coefficients are modified due to their inapplicability for R290/R600a, is established to illustrate the influences of the length of the capillary tube on the performance of the refrigerator. During the investigation a domestic refrigerator of 150L is used to test the thermodynamic cycle performances of R290/R600a (50/50) under conditions with different lengths of the capillary tube. The experimental results indicate that the R290/R600a (50/50) mixture with the optimized capillary length, which was obtained from simulation, has the higher energy efficiency and a lower discharge temperature than the original R12 system. The proposed mixture is proven to be a suitable long-term alternative in terms of its excellent thermodynamic cycle performances.