The flow evaporation heat transfer characteristics of CO 2 and propane mixtures in a horizontal smooth 2 mm inner diameter tube were experimentally investigated. The working conditions included CO 2 and propane composition ratios of 100:0, 75:25, 50:50, 25:75 and 0:100, initial evaporation temperature of 0–10 °C, mass flux and heat flux up to 400 kg m −2 s −1 and 15 kW m −2 , respectively. The results show that the mixture heat transfer coefficient is between that of pure CO 2 and pure propane for the same conditions, and increases with increasing CO 2 proportion and initial evaporation temperature. The dryout vapor quality increases with increasing propane proportion or decreasing initial evaporation temperature. A correlation to predict the heat transfer coefficient for pure CO 2 , pure propane and various mixtures flow evaporation in small diameter tubes with the predictions agreeing well with the experimental data of this and other studies was developed.