Effect of fluid temperature on the frictional coefficient of supercritical pressure water flowing in adiabatic horizontal tubes

• The frictional coefficient (f) of SCW is very sensitive to the fluid temperature.
• Only a 0.5–1.0 °C change in fluid temperature can change the tendency of f–H curve.
• Error of the temperature of SCW in experiments is estimated to be larger than 1.0 °C.
• Both concave tendency and convex tendency are reasonable for the f–H curves.
• Conflict of f–H curves of SCW is due to the uncertainties in the fluid temperature.

Based on the analysis on sensitivity of the frictional coefficient of supercritical pressure water to the fluid temperature, the conflict of the variation trends of the frictional coefficient with the fluid enthalpy obtained by different researchers was explained. It is shown that both concave curves and convex curves are reasonable for the variation trend of the frictional coefficient with the fluid enthalpy. For the same case, the variation trend of the frictional coefficient with the fluid enthalpy might change from concave curves to convex curves, or, from convex curves to concave curves, when the fluid temperature in the calculation of frictional coefficient is changed by a value as little as only 0.5–1.0 °C. The maximum error in the measured fluid temperature is estimated to be large enough (larger than ±1.0 °C), and might be the main reason for completely different tendencies of the frictional coefficient obtained in different studies.