Experimental investigation of heat transfer of supercritical CO2 cooled in helically coiled tubes based on exergy analysis

Experimental investigation of the cooling heat transfer of supercritical CO2 in helically coiled tubes with constant wall heat flux is analyzed based on exergy analysis. The experiment covers an inlet temperature range of 295-330 K, a mass flux range of 159.1-954.9 kg/m2s, a tube diameter range of 2-5 mm and a Reynolds number range of 11,000-90,000. The effects of mass flux, heat flux and diameter of helically coiled tube on the dimensionless exergy destruction are investigated. Experimental results show that the dimensionless exergy destruction caused by the irreversibility of heat transfer is much larger than that by flow friction for supercritical CO2. The optimal Re is more sensitive with mass flux and tube diameter rather than heat flux. For the tube diameters of 3, 4, 5 mm considered, there exists an appropriate range of Re that have the smaller NI and the better exergy utilization with certain diameter. A correlation for the optimal Reynolds number as function of main dimensionless parameters related to wall heat flux, mass flux, fluid properties and geometric dimensions is proposed. These results provide helpful information for the optimal design of helically coiled heat exchanger with supercritical CO2 based on the thermodynamic analysis approach.