Numerical study on the phase change and spray characteristics of liquid ammonia flash spray

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Ammonia is regarded as one of the carbon-free alternative fuels for energy systems. The direct utilization of liquid ammonia in gas turbines can reduce the complexity and start-up time of the system. Liquid ammonia is susceptible to flash boiling because of its low boiling point, especially under standard conditions. The boiling point is 239.7 K under 1 atm, which is different from those of traditional hydrocarbon fuels and brings challenges for liquid ammonia spray and combustion simulation. However, the validity of phase-change models for liquid ammonia remains unclear and needs further exploration. Therefore, the present work aims to numerically evaluate the existing evaporation and boiling models for liquid ammonia flash spray. Large eddy simulations were conducted in the Euler-Lagrangian framework, considering droplet kinetics, evaporation, boiling, radiation, and gas-particle interactions. Specifically, five phase-change models were evaluated by comparing the simulation results with recently published experimental data for the vaporization of the ammonia flash spray in terms of the penetration length, spray morphology, and temperature-diameter distribution law. The results indicated that the combined model (the Zuo model combined with the Langmuir-Knudsen model) was more suitable under superheated conditions and agreed reasonably with the experimental results obtained under various temperature and pressure conditions. The evaporation rate tended to increase with decreasing pressure, leading to a significant reduction in the droplets and gas field temperatures. The interaction between the droplet and gas phases was significantly affected by pressure. The ammonia vapor mass fraction first decreased and then increased with an increase in temperature under low pressure, whereby it exhibited only a positive correlation at high ambient pressure. Finally, the effect of the particle diameter distribution was explored and discussed.

収録刊行物

  • Fuel

    Fuel 345 128229-, 2023-08-01

    Elsevier BV

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