Evaporative cooling by water spray systems : CFD simulation, experimental validation and sensitivity analysis

Evaporative cooling by water spray is increasingly used as an efficient and environmentally-friendly approach to enhance thermal comfort in built environments. The complex two-phase flow in a water spray system is influenced by many factors such as continuous phase velocity, temperature and relative humidity patterns, droplet characteristics and continuous phase-droplet and droplet-droplet interactions. Computational Fluid Dynamics (CFD) can be a valuable tool for assessing the potential and performance of evaporative cooling by water spray systems in outdoor and indoor urban environments. This paper presents a systematic evaluation of the Lagrangian-Eulerian approach for evaporative cooling provided by the use of a water spray system with a hollow-cone nozzle configuration. The evaluation is based on grid-sensitivity analysis and validated using wind-tunnel measurements. This paper also presents a sensitivity analysis focused on the impact of the turbulence model for the continuous phase, the drag coefficient model, the number of particle streams for the discrete phase and the nozzle spray angle. The results show that CFD simulation of evaporation by the Lagrangian-Eulerian (3D steady RANS) approach, in spite of its limitations, can accurately predict the evaporation process, with local deviations from the wind-tunnel measurements within 10% for dry bulb temperature, 5% for wet bulb temperature and 7% for the specific enthalpy. The average deviations for all three variables are less than 3% in absolute values. The results of this paper are intended to support future CFD studies of evaporative cooling by water spray systems in outdoor and indoor urban environments.