Modelling on the dynamics of droplet impingement and bubble boiling in spray cooling

Abstract

A spray cooling model incorporating a spray characteristics submodel and a heat transfer submodel to simulate the dynamics of spray characteristics, droplet impingement, and bubble boiling is presented. The spray characteristics submodel based on a Monte Carlo algorithm simulates the droplet diameter, velocity and spatial droplet flux distributions in actual spray conditions. The heat transfer submodel considers the spray cooling process as film flow boiling to include the processes of droplet impingement forced convection and thin film bubble boiling. Phase Doppler anemometry measurements are used as validation in the spray characteristics submodel, and as boundary conditions in the heat transfer submodel. Reasonable comparison is observed between the experiments and simulations. Parametric effects on the heat transfer performance and bubble dynamics are investigated. The simulation shows that increasing heat flux tends to increase the bubble growing frequency thereby causes the higher bubble collapsing flux and bubble puncturing flux. By fixing the droplet impinging velocity and flow rate, the surface temperature non-uniformity is found to be influenced by droplet diameter. A smaller impinging droplet diameter with a higher impinging droplet flux is favourable to bubble boiling due to more secondary nuclei and larger fractions of bubbles punctured at bigger diameters.