The influence of void fraction on the submerged perforated sheet hydraulic friction factor

The results from an experimental investigation of two-phase flow motion through a submerged perforated sheet (SPS) obtained at the Elektrogorsk Research Center test facility are presented. The test facility, the test section of which is a transverse “cutout” from the full-scale PGV-1000 steam generator with the models of vessel internals, is described in detail. The procedure for carrying out trial startups is outlined, and the system of instrument and control devices is described. The SPS used in all experimental modes of operation had the perforation ratio (the hole area to the sheet area ratio) equal to 5.7%. The pressure in the system was around 7 MPa, and the flow rate of supplied steam was varied from 4.23 to 7.94 t/h, which corresponded to the steam velocity at the evaporation surface equal to 0.15–0.29 m/s. Distributions of pressure difference across the SPS and void fractions under the SPS and above it are obtained. The SPS hydraulic friction factor for a two-phase flow is determined as a result of processing the experimental data. A correction for two-phase nature of the flow for the SPS operating conditions is determined by comparing the obtained SPS hydraulic friction factor for a two-phase flow with the SPS hydraulic friction factor to single-phase flow of steam. It is shown that this correction can be either greater than unity (at low void fractions) or less than unity (at high void fractions).