Experimental investigation on heat transfer characteristics of supercritical CO2 cooled in horizontal helically coiled tube

• The heat transfer characteristics of CO2 cooled in a helically coiled tube is conducted experimentally.
• The gravitational buoyancy and the heat transfer coefficient of helically coiled tubes are higher than that of straight tubes.
• Gravitational buoyancy plays a leading role at low mass flux.
• A new heat transfer correlation of the supercritical CO2 in the horizontal helically coiled tube is proposed.

An experimental investigation on the heat transfer characteristics of supercritical CO2 during gas cooling process in a helically coiled tube is conducted. The experimental data are obtained over a mass flux range of 79.6–238.7 kg m−2 s−1, an inlet pressure range of 7.5–9.0 MPa and a mean bulk temperature of 23.0–53.0 °C. The effects of mass flux, bulk temperature and pressure on the heat transfer coefficient for helically coiled tubes are investigated. A comparative analysis of the gravitational buoyancy and the heat transfer coefficient is carried out between helically coiled tubes and straight tubes. A new heat transfer correlation of the supercritical CO2 in the horizontal helically coiled tube is proposed based on the experimental data. The maximum error between the predicted results of the new correlation and the experimental data is 20%.