Experimental and theoretical studies on the droplet temperature behavior of R407C two-phase flashing spray

•Droplet temperature of R407C spray is reported by experimental and theoretical ways.•High-temperature droplets of R407C spray exist in central region near nozzle tip.•“W” radial temperature distribution converts to “U” shape with spray evolution.•Coupled model predict droplet thermal behavior better than one-way model.•Predictive droplet minimum temperature is independent of droplet initial parameter. Flashing spray is a common phenomenon in many industrial fields. A rapid droplet temperature change in flashing spray is an important feature, which distinguishes this phenomenon from other traditional sprays. This study provides first-hand droplet temperature data of an R407C flashing spray, which serves as a substitute for R22, by conducting systematic experiments. A coupled droplet evaporation model is also introduced to predict the droplet temperature of flashing spray, rather than CFD simulation, for the first time considering the coupling of heat and mass transfer between a droplet surface and its surrounding region of influence. Experimental result shows that droplet temperature first decreases rapidly with axial distance, and then a gradual decrease in the downstream until its minimum value is reached. A hot core is observed near the nozzle exit, where the droplet temperature is higher at the spray center than in its periphery region. Droplet radial temperature distribution becomes uniform in the far spray field. The interaction of heat and mass transfer between the droplet surface and its surrounding region of influence is revealed using a coupled evaporation model. That is, the vapor mass fraction and temperature of the influence region undergo increase and decrease with evaporating time, respectively. Therefore, the coupled evaporation model presents better performance than a one-way evaporation model in predicting droplet minimum temperature. This predictive result agrees well with the experimental data. The minimum temperature of a predictive droplet is independent of the initial diameter and velocity of this droplet.