Numerical study on the spray and thermal characteristics of R404A flashing spray using OpenFOAM

•Spray and thermal behaviors of R404A flashing spray is studied by OpenFOAM.•A non-equilibrium spray region is found near nozzle tip with explosive atomization.•Droplet diameter has a rapid reduction but velocity accelerates near nozzle tip.•A warm core with high droplet temperature exists near nozzle tip.•Contractive spray profile transforms to expansion one with back pressure increasing. Flashing spray is of great importance in a variety of engineering fields, which occurs as the pressurized liquid is released into a low-pressure environment below its saturation pressure. The initial stage close to the nozzle exit is furthest from thermodynamic equilibrium and the information of droplets is difficult to obtain by experimental ways due to the high density of droplets. This paper conducts a systematically numerical study on the spray and thermal characteristics of R404A flashing spray with high volatility and low saturation temperature, based on the open source tool OpenFOAM-2.4.0. Key physics involved in the complex process, including droplet flash boiling, evaporation, droplet transport, breakup, heat transfer and interaction between droplet and gas phases are taken into consideration, through Reynolds Averaged Navier Stokes simulations (RANS) with Eulerian Lagrangian framework for the continuous phase and discrete phase respectively. The spray morphology and droplet diameter coincide reasonably with those in the experiment. It presents explosive atomization with large cone angle and quick expansion towards the radial direction near the nozzle exit. Droplet diameter and temperature undergoes a rapid reduction, while velocity accelerates in this region. A warm core with high droplet temperature exists in the spray central region, and droplet velocity is also larger than that at spray periphery. The ambient pressure significantly affects spray profile, penetration distance and velocity. The whole spray profile transforms to the expansion shape as the pressure increases above 0.5 MPa whereby it presents contractive one in low ambient pressure. Higher ambient pressure leads to lower droplet velocity but with longer penetration distance. These numerical results provide further insight into the mechanism of the flashing spray with volatile cryogens.