Experimental investigations on heat transfer of CO2 under supercritical pressure in heated horizontal pipes

This publication provides a dataset of 54 experiments, carried out with supercritical CO2 (sCO2) in two heated horizontal pipes with inner diameters of 4 and 8 mm at a pressure of approximately 7.75 MPa. The mass fluxes were set to 400 and 800 kg/m2s and the heat flux was varied from 30 to 130 kW/m2, resulting in a heat to mass flux ratio of 38–225 J/kg. The influences of the inner pipe diameter, the Reynolds number and the heat to mass flux ratio on the thermal stratification were studied. Temperature differences up to 90 K between the bottom and the top of the pipe have been detected. By varying the bulk fluid inlet temperature, the thermal inflow lengths have been quantified for a fully developed temperature stratification with up to 180 inner pipe diameters. The Petukhov and Richardson buoyancy criteria show that the experimental results are strongly influenced by buoyancy. For the Jackson buoyancy criterion, a new threshold of higher than 160 is proposed. The validation of four empirical Nusselt correlations shows that the Bishop correlation has the lowest total average deviation of 52%, especially for the bottom site of both pipes with an average deviation of 29%.