A numerical model is presented in this paper, for predicting capillary tube performance using new alternative refrigerants to CFC-502. The model has been established after the fluid flow conservation equations written for a homogeneous azeotropic refrigerant fluid flow under saturated, sub-cooled and two-phase conditions. The study was limited to the following azeotropic mixtures: R-507, R-404A, and quaternary mixture (R32/R125/R134a/R143a). Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R-507 would experience smaller pressure drop across the capillary compared to the other alternatives under question. Copyright (C) 2001 John Wiley & Sons, Ltd.