Numerical Model for Gas-Droplet Flow Application to Liquid Spray and Cooling Towers

摘要

A two dimensional model (axisymmetric or planar) has been implemented to study the gas-droplet flow due to water sprays or in cooling towers. The model consists of coupled sets of equations governing the gas and liquid phases. Modelling the gas phase as a continuum allows use of the Navier-Stokes equations with momentum source terms included. The liquid phase, represented by a finite number of droplet trajectories is governed by the equations of motion of falling spherical droplets subject to gravitational and drag forces. Numerical solutions of these equations is made in an iterative fashion by solving first the liquid phase equations and then the gas phase equations until a steady state solution is reached. Solution of the liquid phase equations by a fourth order Runge-Kutta method, allows subsequent determination of the droplet-gas momentum exchange field. Calculations of the flow field due to an axisymmetric spray shows good agreement with experiment. The degrading effect of wind on a spray curtain is demonstrated, though calculations show that curtain performance may be improved by tilting the nozzle into the wind.