Numerical Study on Air Temperature Reduction by Water Spray
Numerical study was conducted to investigate the water spray cooling effect in an air cooled heat exchanger. A k-ε turbulence model, discrete phase model, and species transport equations were solved simultaneously along with heat-mass exchange model to capture heat and mass transfer effects. The simulation result was compared to an available real scale test data. Using the real scale operating condition, the effect of spray water droplet diameter (10 to 100 μm), spray system configuration (horizontal, vertical, inclined), evaporative time (vertical location of spray system), wind speed (0 to 4.47 m/s), ambient air relative humidity, and spray water amount were investigated. A non-dimensional spray cooling parameter was introduced to evaluate various effects. A parametric study reveals that the vertical location of the water spray system is critical to the evaporative performance and the minimization of adverse wind effects. Securing enough evaporative time by increasing liquid droplet flow path is required to enhance spray cooling effects. It is also found that proper spray nozzle selection (i.e. liquid water droplet size) is critical to achieve desired spray cooling capacity. The spray cooling system design should consider the interactive relationship between the heat exchanger configuration and the local climate condition.
Keywords: Spray cooling, CFD, discrete phase model, evaporative cooling, air cooled heat exchanger