Abstract

This work presents a numerical study on the turbulent flow of air with dispersed water droplets in separators of mechanical cooling towers. The averaged Navier-Stokes equations are discretised through a finite volume method, using the Fluent and Phoenics codes, and alternatively employing the turbulence models k − ϵ, k − ω and the Reynolds stress model, with low-Re version and wall enhanced treatment refinements. The results obtained are compared with numerical and experimental results taken from the literature. The degree of accuracy obtained with each of the considered models of turbulence is stated. The influence of considering whether or not the simulation of the turbulent dispersion of droplets is analyzed, as well as the effects of other relevant parameters on the collection efficiency and the coefficient of pressure drop. Focusing on four specific eliminators (‘Belgian wave’, ‘H1-V’, ‘L-shaped’ and ‘Zig-zag’), the following ranges of parameters are outlined: 1 ≤ Ue ≤ 5 m/s for the entrance velocity, 2 ≤ Dp ≤ 50 μm for the droplet diameter, 650 ≤ Re ≤ 8.500 for Reynolds number, and 0.05 ≤ Pi ≤ 5 for the inertial parameter. Results reached alternately with Fluent and Phoenics codes are compared. The best results correspond to the simulations performed with Fluent, using the SST k − ω turbulence model, with values of the dimensionless scaled distance to wall y+ in the range 0.2 to 0.5. Finally, correlations are presented to predict the conditions for maximum collection efficiency (100 %), depending on the geometric parameter of removal efficiency of each of the separators, which is introduced in this work.

Abstract

The development of a new Reynolds stress model suitable for computations of separated flows is described. It is based on the recently published version of SSG/LRRmodel, which includes a correction eliminating streamline back-bending near the reattachment point. Modifications are proposed which reduce the turbulence kinetic energy dissipation rate and pressure-strain term near the separation point. The validation results using the Diverging channel flow test case are presented. The quality of the obtained results is assessed.