Hydraulic resistance of in-tube cooling supercritical water accompanying out-tube pool boiling

Highlights: • Studied hydraulic resistance of in-tube cooling SCW with out-tube pool boiling. • Existed a steep "pit" for friction factor of adiabatic flow near PC region. • Observed a noticeable "Λ-shaped" profile of the cooling frictional pressure drop. • Introduced deceleration-factor into the cooling friction factor correlation. The experiment was conducted by immersing a smooth horizontal tube in a pool tank to simulate the flow condition of Passive Residual Heat Removal System (PRHRS) in a SuperCritical Water-cooled Reactor (SCWR). Hydraulic resistance and friction factor of in-tube cooling supercritical water accompanying out-tube pool boiling were investigated in this study with test pressure ranging from 23 to 28 MPa and mass flux ranging from 600 to 1000 kg·m⁻²·s⁻¹. The influence of pressure and mass flux on pressure drop in adiabatic and cooling flows was analyzed. This paper also discussed the effect of deceleration in the cooling flow and assessed various friction-factor correlations by employing the experimental data. Results showed that the friction factor of the adiabatic flow exists a steep "pit" approaching to pseudocritical region. A noticeable "Λ-shaped" profile was observed in the vicinity of the pseudocritical temperature, due to deceleration-effect of frictional pressure drop in the cooling flow. The deceleration factor of supercritical cooling flow led to the axial fluid element shrinkage and radial bulk fluid velocity parabolic distribution. Taking into account the effect of deceleration-factor, a modified correlation was proposed for in-tube cooling supercritical water accompanying out-tube pool boiling, of which the average error and root mean square error are −2.51% and 15.28% respectively.