To provide guidance for the flexible operation of 350 MW supercritical CFB boiler

experimental investigations were conducted on the flow and heat transfer characteristics of water with low mass flux in vertical upward smooth tube under subcritical pressure. Flow and heat transfer experiments were performed under the conditions of 12～15 MPa pressure

350～440 kg/(m~2·s) mass flux

135～220 k W/m~2 inner wall heat flux.Furthermore

the dynamic characteristics of the tube were experimentally studied by decreasing pressure and increasing inner wall heat flux

based on the 26 MPa heat transfer experiments. The results of the heat transfer experiments indicate that changing pressure affects the heat transfer performance and enthalpy range of the saturated boiling region. The influence of mass flux on heat transfer performance is only reflected in the sub cooled zone

and the heat transfer performance is enhanced with the increase of mass flux. Increasing heat flux decreases the heat transfer performance in the saturated boiling region. Meanwhile

the correlations of the heat transfer coefficient and friction resistance of water in the tube were fitted based on the experimental data. The dynamic experimental results show that the greater the pressure step

the greater the mass flux increment

and the greater the change in the outlet enthalpy and outlet wall temperature. The step of heat flux only affects the outlet enthalpy and outlet wall temperature. The greater the step of heat flux

the greater the change in the outlet enthalpy and outlet wall temperature. This work can provide guidance for supercritical CFB boiler in low load and flexible variable load operation.