Flow and droplet evaporation characteristics of high parameter temperature and pressure reducing valves under off-design conditions

Abstract

The temperature and pressure reducing valve exhibits complex flow, heat, and mass transfer characteristics under off-design conditions. A three-dimensional simulation model of a multi-stage high-temperature and pressure reducing valve (MSHTPRV) was established through the combination of Euler-Lagrange two-phase flow and droplet evaporation models. The temperature and pressure reduction mechanism, as well as the thermal-mass transfer characteristics during droplet evaporation, were investigated. The influence of valve opening on steam flow rate, thermal-mass transfer capabilities, and flow field characteristics was analyzed. The results indicate that the flow rate increases significantly within the 30%–40% opening range and exhibits relatively slow growth in the 60%–100% range. The pressure, temperature, and turbulent kinetic energy inside the valve all decline as the valve opening decreases. When the valve opening is reduced from 100% to 30%, the average pressure inside the valve decreases from 7.65 MPa to 6.88 MPa, and the average temperature drops from 728.29 K to 713.89 K. The mass fraction of newly evaporated steam at the wall above the second-stage throttling orifice plate increases from 0.13 to 0.27, while the turbulent kinetic energy at the right wall of the first-stage throttling orifice plate rises from 4039 m²/s² to 31,708 m²/s². The vortex motion of steam between the first- and second-stage throttling orifice plates intensifies, enhancing the mixing of steam and droplets and accelerating droplet evaporation, thereby improving the cooling effect. After passing through the third-stage throttling orifice plate, both the eddy viscosity and turbulent kinetic energy decrease, reducing heat and mass transfer capabilities. At a valve opening of 50%, the droplet evaporation rate reaches its maximum at 90.9%, but the energy loss due to steam work increases.