The performance of droplet evaporation model in predicting droplet dynamics and thermal characteristics for R134a single isolated droplet and two-phase flashing spray

摘要

Flashing spray with low saturation point and high volatility mediums is of great importance in aerospace field. It involves complex droplet dynamics and heat and mass transfer processes in a turbulent, two phase flow. This paper comparatively evaluates the predictive performance of a selected number of droplet evaporation models that focus on convective and blowing effects. The studies span from a single, isolated R134a droplet that evaporates in a convective environment, to a fully turbulent, flashing spray formed through an accidental release of high pressure R134a liquid. An in-house developed code for single isolated droplet evaporation and a modified sprayFoam solver in OpenFOAM for flashing spray are used to calculate droplet and spray behaviors. The results show droplet evaporation model greatly affects the evolutions of droplet diameter, velocity and temperature for single isolated R134a droplet, that the C-R-S model predicts the lowest droplet diameter and velocity, and highest droplet temperature; the H-N-R model predicts the largest droplet velocity and lowest temperature; the A-S and N-G-R-M models predict almost identical results. In contrast to the great impact on droplet evolution for single isolated droplet modeling, droplet evaporation model has little influence on spray and thermal characteristics for R134a two phase flashing spray simulation. However, the A-S model predicts quite different radial profile of droplet temperature at spray periphery compared with other models, which is much lower than the experimental value. (C) 2019 Elsevier Masson SAS. All rights reserved.