This study covers a comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture under supercritical conditions. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 degrees C-90 degrees C) and pressures (5 MPa-30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the ethane and azeotropic mixture as a new heat transfer fluid was investigated and compared to pure CO2. Total and supercritical-side heat transfer coefficients were obtained around the critical point of the fluids investigated. The influence of temperature, pressure, water flow rate and bouncy force on the heat transfer coefficients were examined. It was found that the azeotropic mixture absorbs a satisfactory amount of heat in the heat exchanger and behaves similarly to pure compounds. Additionally, to properly evaluate the potential and the performance of the CO2-ethane azeotropic mixture, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system that contains exclusively CO2. (C) 2018 Elsevier Ltd. All rights reserved.