Experimental study on single-phase frictional pressure drop for water flow under high heat fluxes

Pressure drop is one basic issue for the heat-removal systems for high heat flux components, such as the ITER divertors in fusion reactors, in which an accurate knowledge of single-phase frictional pressure drop is fundamental for further calculation of two-phase frictional pressure drop. However, the single-phase frictional pressure drop is still not well examined under high heat fluxes. In this study, experiments were conducted on the single-phase frictional pressure drop of water flow in circular tubes within the range of q = 5-10 MW/m2, G = 6000-10,000 kg/m2 s and p =  3-5 MPa (typical operating parameters for water-cooled divertors). The data were correlated using the equation of f/fad =(μw/μb)m, in which m is an empirical exponent. It is found that the exponent m is affected by the length-to-diameter ratio of flow channel, while the effects of mass flux and heat flux are insignificant. In addition, a number of existing correlations for single-phase friction factor were compared with our data. The results indicate that these correlations cannot well capture part of the data. Therefore, a modified correlation is proposed to calculate the single-phase friction factor under high heat fluxes, in which the effect of length-to-diameter ratio is taken into account. The new correlation has an improved performance compared with the existing correlations.