Flash-boiling effect on the droplet size distribution in low-pressure sprays formed at various ambient pressures and liquid temperatures — Experimental study and modelling

Abstract

Flash-boiling injection occurs when a liquid is injected into an environment below its saturation pressure. It can be achieved either by reducing the ambient pressure or preheating the injected liquid. The goal of this work was to understand the influence of flash boiling on the droplet size distribution, depending on how it was achieved, and to model this influence in the function of the superheat parameters. For this purpose, systematic experimental tests were conducted, which covered a broad spectrum of fluid temperature and ambient pressure conditions. The tests showed that both liquid temperature and ambient pressure affect the droplet size distributions. Moreover, depending on the way of achieving flash boiling, the results were substantially different, even though the same superheating, expressed as the saturation to ambient pressure ratio, was maintained. Nevertheless, a similar and consistent pattern of droplet size reduction could be observed between the data series grouped by liquid temperature. Based on the experimental results, a model for simulating droplet size distribution at given superheat conditions was proposed. It takes into account the global trend of droplet size reduction observed for each fluid temperature. The model was found to simulate the droplet size probability density functions with satisfactory agreement under all performed experimental conditions.