Supercritical carbon dioxide (SCO2) is a promising working fluid for the cryogenic refrigeration, air-condition and heat pump systems. The present study sets up a SCO2-water test loop to study the heat transfer performance of SCO2 in a double pipe heat exchanger. The effects of SCO2-side pressure, mass flux and buoyancy force as well as water-side mass flux are investigated. It is found that the total and SCO2-side heat transfer coefficients reduce as the SCO2-side pressure increases. The peak total and SCO2-side heat transfer coefficients appear at a higher temperature than the pseudo critical temperature. The water-side mass flux has a larger effect on the total heat transfer coefficient compared to the SCO2-side mass flux in the studied cases. The contribution of buoyancy force to the heat transfer performance is large at the small SCO2-side mass flux and it becomes smaller as the SCO2-side mass flux increases. The SCO2-side pressure and water-side mass flux have little effect on the buoyancy force. A heat transfer correlation that includes the effect of buoyancy force is obtained by fitting the experimental data with genetic algorithm. (C) 2015 Elsevier Ltd. All rights reserved.