The impact of water spraying on condenser vacuum and hydraulic resistance

Abstract

Relevance: additional water spraying systems used to improve vacuum in industrial condensers are typically installed at the condenser inlet section. The sprayed water droplets begin to interact with the steam flow already in the inlet zone, creating local hydraulic resistance. Determining the magnitude of this local resistance and its impact on the overall vacuum is an important scientific and practical task.

Aim: to accurately calculate the local hydraulic resistance arising from water droplets sprayed by nozzles installed at the condenser inlet section and to assess its effect on the condenser vacuum.

Methods: The study analyzed the two-phase flow in the inlet section of a horizontal condenser with 168 tubes (steam inlet area 0.24 m², flow cross-sectional area between tubes 0.13 m²). The steam flow rate was 806 kg/h = 0.224 kg/s, pressure 4 kPa, density 0.028 kg/m³, inlet velocity 33.3 m/s. The additional water flow rate was 279 kg/h (0.0775 kg/s), nozzle pressure 0.2 MPa (2.0 bar), droplet velocity 14.0 m/s, droplet diameter 1.0 mm. Droplet concentration, aerodynamic drag force, and turbulent mixing resistance were calculated. The variation of resistance was analyzed depending on parameter changes (water flow rate, droplet diameter, steam velocity, nozzle pressure, scheme type).

Results: the local hydraulic resistance in the inlet section is 1.83 Pa (0.00183 kPa). This is only 0.44% of the total two-phase resistance (0.413 kPa). The effect on vacuum is 0.014 mmHg. When the water flow rate increases from 100 kg/h to 300 kg/h, the inlet resistance increases from 0.66 Pa to 1.96 Pa. When the droplet diameter increases from 0.5 mm to 1.5 mm, the resistance decreases from 2.05 Pa to 1.73 Pa. When the steam velocity increases from 25 m/s to 40 m/s, the resistance increases from 1.10 Pa to 2.46 Pa. When the nozzle pressure increases from 0.1 MPa to 0.4 MPa, the resistance slightly decreases from 1.88 Pa to 1.76 Pa. Among the scheme types, the highest resistance is observed in the counter-flow scheme relative to the steam flow (2.05 Pa), and the lowest in the co-current flow scheme (1.83 Pa). Although the counter-flow scheme slightly increases resistance, it improves heat transfer and increases condensation efficiency. Analyses show that water droplets absorb the kinetic energy of the steam, sharply reducing its volume, which positively affects the overall hydraulic conductivity of the device.