Experimental studies on heat transfer to supercritical water in circular tubes at high heat fluxes

Experimental studies on heat transfer to supercritical water flowing upward in circular tubes are carried out at the SWAMUP test facility. Totally more than 10,000 test data were obtained in tubes of two different inner diameters, i.e. 10.0 mm and 7.6 mm with the following test conditions: pressure from 23.0 MPa to 26.0 MPa, mass flux from 450 kg/m2 s to 1500 kg/m2 s, heat flux from 190 kW/m2 to 1400 kW/m2 and bulk temperature from 240 °C to 460 °C. Each test point is accompanied with systematic error analysis. It is found that for 90% of the test data the uncertainty of measured Nusselt number is less than 10%. Based on the test data obtained, the effect of various parameters on heat transfer is investigated, such pressure, mass flux, heat flux and tube diameter. In addition, the importance of several dimensionless numbers and the accuracy of five widely applied heat transfer correlations are assessed. It is concluded that the acceleration number πA and the buoyancy parameter πB show unique effect on heat transfer coefficient. Among the five selected heat transfer correlations, the correlation of Cheng et al. and Jackson show the best agreement with the present test data.